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Concepts for chemical reaction monitoring (37 replies)1.Salvaging a large gas discharge lamp starter (5 replies)2.Ultrapowerful Electroshock (13 replies)3.Darpa Grand Challenge won. (0 replies)4.Coil Driver HV Generator (20 replies)5.


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The Explosives and Weapons Forum > DIY Engineering > Electronics > Coil Driver HV Generator

View Full Version : Coil Driver HV Generator

July 19th, 2002, 06:59 AMxyz

I recently made an ignition coil driver and thought I w ould post some pics of it. I know it doesn't really fit the topic of improvised weapons as it need to be plugged in but thisboard is w here PYRO500 posted his pulse capacitor briefcase and this topic doesn't really fit anyw here else.

Here is a pic of the whole coil driver set up, the big silver thing with the black top that's standing on a stack of tiles is a car engine ignition coil, the tiles are to stop it from arcinginto the ground,and the top has been coated in hot glue to stop it arcing up there. The other two things are a 2Kv 1.1uf capacitor (from a microwave) and two dimmer switchesto control the output (the kind used for lighting, this circuit will still work w ith only one but I put 2 in for better output control). The pic is about 40kb.<a href="http://www .boomspeed.com/theprodigy/xyzcoildriver.jpg" target="_blank">Coil Driver</a>

Here is a pic of the fury of sparks which jump rather noisily betw een the output w ires, the gap in the photo is about 3cm wide but the sparks can jump up to about 5cm. This picalso about 40kb.<a href="http://www .boomspeed.com/theprodigy/xyzcoildriveroutputs.jpg" target="_blank">Coil Driver Output Wires< /a>

The parts are quite easy to find and any capacitor in the range of 600v upwards and about 0.5 - 2 uf will work (different capacitors give different frequencies and spark lengths)although when I tried a 350v 120uf camera flash capacitor it thermally failed quite spectacularly filling the garage with smoke :) .These things are useful for frying just about anything that contains electrical circuitry (I already tried a toy bob the builder w alkie talkie :D )and will punch a tiny hole throughanything non conducting and thin enough that gets in betw een the terminals (sheets of paper or thin plastic.

July 19th, 2002, 10:55 AMPYRO500

Incase you or anyone reading this dosen't know how this thing is woking this circuit uses the light dimmer witch clips the waveform of the w all ac to cause lights to go dimmer,this clipped ac charges and discharges the capacitor through the ignition coil causing it to resonate and saturate the coil and you can thus draw power from the output.I think the most practical use for these devices is a charger for an electric defense shield although I don't think that you should let one of these run for an extended period oftime as I think it could wither damage the dimmer unit, the coil or cause a fire or something.

July 19th, 2002, 07:06 PMxyz

I thought dimmer switches are just variable resistors that serve to increase or reduce the pow er, it still w orks when they are both set to have no effect (i.e. set to full power,their range is 14% to 100% of the total power). The coil is a large one and I have noticed no change in temperature after the circuit has been on. If any part were to getdamaged I would expect it to be the dimmer switches or the operator :D . BTW I just thought I w ould also mention something that you forgot to say Pyro, the coil works bybuilding up a magnetic field and then collapsing it, so it sparks once w hen the current is turned on and once when it is turned off again, I think PYRO500 mentioned that thecapacitor is what turns it on and off very fast by charging and discharging.

Edit: Spelling

[ July 19, 2002, 06:08 PM: Message edited by: xyz ]

July 19th, 2002, 09:18 PMPYRO500

While a variable resistor would work for dimming a light it would not only get hot but it w ould not give linear dimming. I mean by liner dimming in that when you turn the knobthe bulb's dimming would be continuously variable by the amount you turn it and it w ould not dim faster or slow er at low er or higher settings.

The w ay these dimmers w ork is by clipping the top and bottom of the ac wave causiing the peak voltage to be reduced. the capacitor charges and discharges with ac where aswith dc it will charge then block the current.

July 19th, 2002, 10:24 PMxyz

Ok then, I'll remember that. They have coils of wire inside them (you can see them from the outside, I haven't dismantled one) which is why I assumed they were variableresistors. I have potted the coil in wax now to insulate it from the ground and it's surroundings and to prevent all arcing (the hot glue w asn't doing a satisfactory job) and I amcurrently waiting for it to cool down and solidify so I can test it.

Edit: Just adding that I can see it's potential as a very pow erful (and probably lethal) electric fence, you could simply make a wire fence that was well insulated from the groundand then connect the positive terminal of the coil to it. When something touches the fence w hile it is also touching the ground, BZAAAP :) . You could also use the dimmers toadjust the fence to anything from Ouch, my finger! to Oh No! I'm Dead or seriously injured by a 50 Kv electric fence!


July 19th, 2002, 10:59 PMPYRO500

I would try using diffrent capacitors instead of changing the voltage. the way the circuit works is that it continuously charges and discharges the capacitor every cysle so lesscapacitance means less energy. To reduce capacitance you could hook the capacitors in series w itch would allow you to use higher voltages (although you won't be) and will cutthe capacitance in half.

July 20th, 2002, 12:06 AMxyz

It w orks well with no arcing whatsoever now the w ax has cooled. Smaller caps does mean smaller discharges but I'm pretty sure it also means more rapid ones because it takesless time to charge and discharge, why bother changing the caps when you just turn the dimmer dial down and the sparks are smaller and less pow erful but just as rapid.


July 20th, 2002, 12:24 AMPYRO500

As far as I know the frequency of the sparks in this circuit cannot be determined by the capacitor, you must change the input frequency to change the output frequency witchunder us power is 117V average (around 170 peak).

July 20th, 2002, 12:59 AMxyz

The site w here I got the plans (these are not plans for US pow er, they are designed for use in the UK, Australia, New Zealand, Or anywhere else tha uses 240v 50hz)said thatdifferent caps give different frequencies. Mine makes about 25-30 sparks in a second and is definitely slower than the 50hz that our mains pow er supplies. The cap in the planswas a 600v 1uf and I am using 2000v 1.1uf w hich I think is w hy I am getting slower sparks. I should get 100 sparks a second w ith 50hz mains pow er (the rate it sparks isdouble the frequency because the coil sparks once when turned on and once when turned off again so turning on and off 50 times a second gives 100 sparks a second).

July 20th, 2002, 01:26 AMPYRO500

Technichly you should get the same amount of pulses no mater what capacitors you use beacuse the capacitor is being driven by the line pulses witch continually charge anddischarge each cycle, it's possible that the pulse is sw itched off or something but I can't remember what the waveform of these looks like. I think with a smaller amount ofcapacitance you should be able to get a higher voltage at a lower energy allowing you to have a safer HV supply.

July 20th, 2002, 01:45 AMxyz

2000v 1.1uf IS high voltage low capacitance (and a lot more so than the 600v 1uf one which was recommended for this circuit). Anyway, I found it to be extremely good atdestroying CDs, w hen a CD is placed between the teminals the electricity arcs all over it burning off all that shiny material and after about 2mins or so you have a perfectly clearplastic CD :) .

July 20th, 2002, 03:51 AMPYRO500

It does not matter what voltage capacitor you use in your setup as long as it exceeds the maximum voltage of your circuit.A bit here on the energy in capicitors, The energy in capacitors is determined by the formula (0.5C)(V^2) or if your calculator dosen't screw order of operations up 0.5*C*V^2= J.In that formula C=capacitance in farads (caps are usually marked in micro farads)J=joules (Watts*1second) and V= voltage.If you look at this formula carfully or even plug some numbers into it you will see that the voltage has an exponential increase in energy as the voltage increases while thecapacitance (w itch is halved to start with) is only having a liner effect on the energy.

If you were to plot a capacitor's energy w hile charging with this formula (energy= vertical voltage=horizontal) you would see a line that formed a curve that would becomeincreasingly steeper untill it eventually became almost vertical and impossible to graph by hand.

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I'll do some math for you to show you an example of the energy in this cap:

your capacitor is 1.1UF so C= 0.00000011/2 (that's 0.000000055) and the maximum voltage is 2000V so that squared is 4000000 and 4000000*0.000000055= 0.22J

now that's at maximum charge of 2000V but your capacitor can only charge to say around 200V when you have the dimmer on at a safe setting so I'll spare you the math andtell you that the energy at that it has at 200V is 0.022J w itch is the energy per spark witch you say happens around 30 times a second witch means .66J in one second, notnecessarily lethal but sure to be painful.

[ July 20, 2002, 03:03 AM: Message edited by: PYRO500 ]

July 20th, 2002, 04:22 AMxyz

I have both dimmers set at full power all the time as I have noticed no heating up or anything like that after the circuit has been running. You can smell the ozone quite stronglyafter about 2 mins.

0.66 Joules a second isn't very much :( (about the same as being shocked from a camera flash cap),I'm sure it must be more than that because it takes 4.2 joules of heatenergy to raise the temperature of one ml of water by one degree celsius and I have watched it burn the coating off CDs at a reasonable rate not to mention that lots of theelectrical energy is expended as light and sound as w ell as heat.

Also, If the capacitor can be any value so long as it is higher than the circuit, and the circuit is 240v w ith a possible maximum of 250v, how come my 330v flash cap blew whenI tried that?

July 20th, 2002, 09:25 AMPYRO500

I think I may have had a small error in my math, I neglected to take into consideration the reverse charging of the capacitor during discharge, so that's 1.12 J w itch is less thana camera flash cap the most common ones in disposable are around 6.5J. But remember now, your camera flash circuit makes quite a bit of noise it self when shorted and ptsout a fair amount of energy. your coil on the other hand is high voltage witch can take that energy and push it through conductors your 330V camera flash can't go such asthrough the metalic layer of a cd by arcing through it.

The capacitor can't really be any value, for one the camera flash capacitors aren't AC rated, in fact the fit in a catagory of capacitors called electrolytics w itch only are supposedto be charged in one polarity( the negative side is indicated by either a stripe dow n the side or a negative sign on that side or both), by hooking the tiny photoflash capacitoryou basicly took a capacitor that w as designed for a very quick pulse once in a while that also was supposed to be charged in one direction, and you set it up in a circuit that itwas continuously charging and discharging in opposite directions 100 times a second. You never did show me the circuit that you were using, just to be sure I have the right ideaabout your device can you show us a link?

[ July 20, 2002, 08:34 AM: Message edited by: PYRO500 ]

July 20th, 2002, 08:54 PMxyz

Here is the circuit diagram for my coil driver:<img src="http://ww w.boomspeed.com/theprodigy/coildrivercircuit.gif" alt= " - " />The original circuit had only one dimmer and used a 600v 1uf capacitor. Polarity is not marked on the coil because my coil is marked for use in a car engine and doesn't saypositive and negative, I just make sure that the wire coming out of the top of the coil is the one that wants to ground itself (i.e. is the one that shoots purple sparks into thefloor when placed above the floor and the coil driver turned on)I also think that it may possibly set someones clothes on fire if they got stuck on it for more than 2 seconds, it takes about 2 seconds to set paper on fire w hen it is placed inbetween the terminals.

July 21st, 2002, 08:40 PMAnthony

Uhhh, the coil on a car engine *does* stay at the same polarity. The casing is connected to negative, the centre connection in the top is HT out, then there's a positive triggerfrom the distributor, usually to the side.

I think I remember seeing a similar circuit, but without a capacitor. I presume this would still work as the magnetic field in the coil should still collapse on every cycle? Or doesthe cap serve to rectify the AC to DC and the coil will only work if fed DC?

July 21st, 2002, 09:07 PMPYRO500

I think it'd be a good idea to keep the capacitor. The capacitor is what limits the power every pulse to tw ice the energy of the capacitor. This w orks by the AC cycle charging thecapacitor one way then on the voltage reversal the power discharges the capacitor and charges it the other way and so on.

July 22nd, 2002, 05:04 AMxyz

Anthony, w hat I meant is that the coil is not marked positive and negative, one side is marked as battery and one side as something else. I can still use it fine w ithout themarkings anyway.

When I had just started building this and hadn't yet got hold of a suitable capacitor, I tried it without the capacitor, it sparked once (rather weakly as w ell) and then the circuitbreakers tripped and cut off the house's power supply. It needs the capacitor and the dimmers to work (tried it w ithout the dimmers out of curiosity and it did nothing at all).

The coil works fine when fed AC (I have run it on 12 volt 15 amp AC, it worked but the sparks were only about 0.3cm long and it only sparked once when turned on and oncewhen turned off as there was no capacitor to pulse it)and I don't think that the capacitor serves as a rectifier.

July 22nd, 2002, 05:48 AMPYRO500

You shouldn't run these things from AC for one the reason it didn't arc very far is that it needs pulsed power from a source such as a light dimer.

July 23rd, 2002, 06:43 AMxyz

I don't use the 12v AC because I have my capacitor and dimmers now and can run it from 240v.

[ July 23, 2002, 05:47 AM: Message edited by: xyz ]

March 17th, 2008, 07:45 PMETCS (Ret)

The Incandescent Lamp Dimmer circuit is based upon a Thyristor (Triac) w hich is adjusted to change the angle of conduction of the incoming AC current. By rotating theadjustment potentiometer on the dimmer, the incoming AC sinusoid waveform is is blocked until the Triac is triggered "on" at the desired angular position of the waveform,thereby reducing the time of current flow during each half cycle.

The output waveform of the dimmer, at other than full brilliance, is more like a pulse than a sinusoid; at the instant of "turn on" when the Triac goes into conduction the outputvoltage instantly jumps to the insantaneous value of the input voltage, and the output voltage continues along the sinusoidal track of the input until it reaches zero volts whichwill sw itch the Triac "off" until the next half cycle turns it on again at the set point of the dimmer adjustment.

To power an induction coil (Ignition Coil) with a Dimmer it is absolutely necessary to use a Capacitor in the current path to the Coil. The Capacitor must be "Non Polarized" andcapable of use in Alternating Current applications.

A DC Electrolytic Capacitor will not work as it will be destroyed by the Alternating Current flow.

The brief "charge" and "discharge" pulses of the capacitor through the primary of the coil is w hat produces the high voltage discharge at the output terminals of the coil.

For best and safest operation the Capacitor should be One to Two Microfarads with a Voltage Rating of more than 250 Volts for 120 Volts AC operation.



The Explosives and W eapons Forum > DIY Engine ering > Electronics > Darpa Gra nd Challenge won.

View Full Version : Darpa Grand Challenge won.

Novem ber 3rd, 2005, 09:21 PMJacks Complete

Volk swagen W ins Pentagon Robot RaceAssociated Press | O ctober 10, 2005PRIMM, Nev. - A driverless Volkswagen won a $2 m ill ion race across the rugged Nevada desert Sunday, bea ting four otherrobot-guided vehicles that completed a Pentagon-sponsored contest aim ed at m aking warfare safer for hum ans.

The race displayed m ajor tech nological leaps since last year's inaugural race, whe n none of the self-driving vehicles crossedthe finish line.

Stanley the VW Touareg, designed by Stanford University, zipped through the 132-mile Mojave Desert course in six hours and53 minutes Saturday, using only its com puter brain and sensors to navigate rough and twisting desert and m ountain trails. TheStanford team celebrated by popping champagne and pouring it over the m ud-covered Stanley.

"This car, to m e, is really a piece of history," Stanford com puter scientist Sebastian Thrun said after receiving an oversizedcheck for the $2 mill ion prize, funded by taxpayers. He said he did not know how he would spend the m oney, but jo ked that heneeded to buy cat food.

Stanford spent $500,000 on the race, som e of which was provided by sponsors.

In second place was a red Hum vee from C arnegie Mello n University called Sandstorm , followed by a custom ized Hum mer calledH1ghlander. Coming in fourth was a Ford Escap e Hybrid named Kat-5, designed by students in Metairie, La., who lost about aweek of practice and som e lost their hom es when Hurricane Katrina blew into the Gulf Coast.

The Humvee, which finished in seven hours and four m inutes, traveled farther than any other vehicle last year despitecompleting o nly 7 1/2 m iles of the cou rse.

A fifth vehicle, a 16-ton truck nam ed T erraMax, was the last to finish the course Sunday, though not within the contest's 10-hour deadline. Its operators p aused it Saturday night so it wouldn't have to race in darkness.

It's unclear how the P entagon plans to harness the tech nology u sed in the race for m ilitary applications. But Thrun said hewanted to de sign autom ated system s to m ake next-generation cars safer for eve ryone, not just th e m ilitary.

"If it was only for the military, I wouldn't be here today," Thrun said.

Volk swagen plans to use Stanley in prom otions, and the vehicle will then be retired to a m useum in Germany, Thrun said.

Called the Grand Cha llenge, the race began Sa turday with a field of 23 autonom ous vehicles. Eighteen failed to com plete thecourse because of m echanical failures or senso r problems. Even so, most covered m ore distance than Sandstorm did last ye ar.

Race organizers and team m embers say im proved technology and a fam iliarity with the ra ce allowed m ultip le robots to sprintacross the finish line.

Even before Saturday's com petition, te ams practiced their vehicles in various parts of the Southwest desert, including on lastyear's course. Teams also went back to the dra wing board to im prove their vehicles' artificial intelligence an d sensing system s,which navigate the rough landscape without crashing.

The vehicles were tricked out with the latest sensors, lasers, cam eras and radar that feed data to onboard computers, whichhelp ed them distinguish dangerous bo ulders from tum bleweeds and decide whether chasms were too deep to cross.

The robotic vehicles had to na vigate a course d esigned to mimic driving conditions in Iraq and Afghanistan. The courseconsisted of winding dirt trails and dry lake bed s fil led with overhanging brush. Pa rts of the route forced the robots to zipthrough three tunnels designed to kno ck out their GPS signals.

Only the five robots that com pleted the course managed to m aneuver a steep 1.3-mile m ountain pass known as "Beer BottlePass" f ive miles from the f inish l ine. The moun tain ridge - sim ilar to m ountain canyons found in Afghanistan - was only 10 feetwide and had a 200-feet drop-off.

The turning point occurred Saturday when Stanley overtook the top-seeded H1ghlander at the 102-mile ma rk.

The race is p art of the military's effort to fulfill a congressional m andate to cut casualties by having a third of the military'sground vehicles unm anned in 20 years.

A sm all fleet of autonomous ground vehicles currently o perate in Iraq and Afghanistan, but the m achines m ust be rem otelycontrolled by a soldier who usually ride s in the sam e convoy.---

Though I should post about this, since it is so m omentus. Probably 50% of the world's population couldn't have driven thatcourse in tha t time.Obsolete? Moi?


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The Explosives and Weapons Forum > DIY Engineering > Electronics > Ultrapowerful Electroshock

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April 21st, 2006, 07:47 PMsimply RED

Here is the scheme of the most powerful electroshock device I w as able to make.

Characteristics:10 kV DC ; charging 30n ; 15-20Watts consumation ; running on 9-10V.

Schematics:T1-T2 form a multivibrator that generates "sound" frequency (never measured it exactly, anyway it is less than 1 kHz)T3 is an amplifier in "switch" regime. The diode in its base discharges the 33micro cap w hen T2 is open.T4 is non phase reversive amplifier. The 110 ohms in its base adjusts the amperage in its collector chain (2-3A pulse).

The high voltage transformer is a coil from a car (used for fuel ignition).D1:4 form a Gretc (how is his name spelled in English?) scheme and finally the capacitors are charged w ith the 10kV DC.

Anyone even w ith no background in electronics is able to make the scheme. The problem maybe finding the high voltage diodes and capacitors.I used KC106G Soviet made diodes (2 in paralel !, 8 diodes for the cascade) and PTO - 10n ; 5% ; 7,5kV capacitors (2 or 3 in paralel).(never been able to find better capacitors)

The first picture is the schematic plus some diodes and their pasport - the second is the completed device on a test table.

Note that high voltage is dangerous - this thing fries mice and will most possibly do the same to more sophisticated life forms :) . Do not touch either of the poluses even beeingit a DC!!! Work with protective gloves and plastic instruments to handle and test in the final phases.(the best experiment is on a green leaf, the sound from discharges can be heared in the whole house and finally the leaf "burns")

April 22nd, 2006, 11:25 AMJacks Complete

Nice.

Getting a HV coil from a car might be quite a lot harder than getting the diodes and stuff, depending where you are. A scrap yard will have the HV part, it's the bit under thedistributor cap. Diodes can be gotten from many places, but they all need to be rated to whatever the highest voltage in the scheme is, otherw ise they will short or fry or both.

April 22nd, 2006, 01:14 PMsprocket

These coils are actually probably the easiest part to get. They are called ignition coils and are sold at pretty much every car part store. They come in many different sizes andshapes, the larger are typically oil cooled. I've noticed no considerable difference in performance betw een large oil cooled ones and smaller air cooled. In fact the smaller aircooled are marketed as "high performance".

I've built a fairly simple 555-based driver circuit with variable frequency to power these coils according to the schematic found on this page: http://w ww.geocities.com/capecanaveral/lab/5322/coildrv.htm. It's hardly lethal, putting out about 1mA at 30kV, but it really hurts to get shocked by.

I also built a HV capacitor by wrapping the outside of a PP box w ith Al-foil and filling it w ith salt water. The foil is best used as ground and the salt water then becomes the HVside. According to my multimeter it has a capacitance of 0.9nF w hich isn't a lot, but it does make fat loud sparks when discharged.

April 22nd, 2006, 09:35 PMChris The Great

Just ask them for the coil, that is how I got one. But I overdrived it making 2 inch sparks and it died on me.

I'll try adapting this circuit to use the much smaller coil that comes in a law n mow er since I still have several of those. Old crappy lawn mowers are cheap to buy at garage salesor even cheaper at the dump!And of course, assembling it to fit within a handheld device.

Your setup looks like a lot of my electronics projects there Red ;)Thanks a lot for this circuit. I can put together some electronic stuff and understand it well, but designing circuits.... nope, I'm clueless!

April 23rd, 2006, 03:08 AMsimply RED

Success here lies in using switch regime amplifier (T3) with diode in its base (the n of the diode matches the p of the transistor). This way you have conductivity in both half-periods (after the 33 micro you have AC) without applying I(0) to T3. The first half period when T2 is closed - T3 is open - currency flows through - base of T3- charging the33micro and through the 300 ohms. The second half period T2 is open. The 33micro discharges through the diode and T2 collector chain.

Device in action :

FLASH - arc passes through a green leaf (about 2cm).Fl1 - arc travels 0,5 cm through the air (the green leaf is seen on the right of the electrodes).

In order to catch the flash I made small movies and then cut frames from them.

April 28th, 2006, 06:52 PMMarvin

Might be worth thinking about how things like Stun guns work.

They generally step up to an intermediate DC voltage set by the voltage of a really big electrolytic capacitor, then when you want to zap someone they dump this by a fastswitching mechanism, like a thyratron or a big transistor into the primary of a second coil that steps up to 50Kv or so. The output of the second coil then goes outside the boxdirectly.

Key things here,Since the intermediate voltage is set according to the best capacitor available, you have a higher energy pulse for a given weight/size.Secondly since the second transformer is fed in a single pulse the pow er is much higher.

April 29th, 2006, 05:09 AMsimply RED

Schematics using intermediate DC need (at least) two times more elements than this direct solution (and is impossible to be made by a non-professionalist in electronics). Thepower at the end is about five times lower because the losses in the final coil (w hich needs to be special production and is not even available on the market) are very high.The best device I've seen acc to the intermediate voltage scheme had stunning :) complex schematic plus special production final coil (homemade of course - everything on themarket is pure crap) and the flash was like 2 mm wide. Here flash is 4-6 mm wide with about four times less elements.

Directly discharging capacitors into the victim was chosen - best solution after some years of experiments [see the pictures of the flash] :) .

(note - the higher the voltage - the more q (I=q/t) the capacitor gets, w hich means - even low capacity caps w ill be charged "w ell" if the voltage is high)

April 29th, 2006, 08:22 AMJacks Complete

I've got to agree w ith simply RED on this. Fewer parts = cheaper and more reliable. Coils are a bugger for burning out, w ith the resultant arcing setting things on fire or leavingyou w ith a dead device and a strange smell.

0.9nF isn't bad for a really high voltage capacitor, btw. It mostly depends on size, though, since you are limited by arc burn-through of the insulator material(s) and/or the oil/airgaps. Reading up on HV laser capacitors is interesting, I recall a few very smart designs. Using polythene as the dielectric is a great pow er booster, and thick tinfoil is a goodconductor for it.

The easiest design I recall was a roll of foil and polythene in a plastic tube with oil for cooling.

Basically, buy some polythene on a roll, thin stuff, and the thickest foil you can get without crinkles in it. (Try to get the MSDS for the polythene, which should tell you thethickness, and you can look up the dielectric strength and calculate the expected breakdown voltage for two layers.) Now take your clean work surface, and unroll the foil. Youwant a long length of it flat on the table. Now take your polythene, and overlay it. You need at least an inch both ends and sides to stop arcing around the insulator. Now repeattw ice more. This ensures no thin spots blow your cap. Next add the other sheet of foil. Avoid any metal bits on anything, and ensure the edges are as smooth as you can getthem. You might w ant to fold them over or something, rather than cut them to size. Now , w rap one layer of the three layers of plastic over the edge of the foil on both longsides. (That step is optional)

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http://www.geocities.com/

Add two tabs for your discharge. One either end on the same side, keep them fat and thick, and multi-stranded copper is better than bar, and more strands is better, and spreadthe ends out so that the discharge isn't coming through one tiny bit of foil. Solder these on well. You will need flux to get rid of the aluminium oxide that will otherwise insulateit. Smooth the solder off. You might need to insulate one or both leads, too.

Now, carefully roll up your capacitor. Roll it as tight as you can. Keep it tight with a zip tie or three, and then put it in a plastic tube with a sealed end cap or some kind ofcontainer that will not melt from oil.

Add some oil to a bit over the top of the roll, and there you go! You will be able to run this to pretty high voltages (1kV+, you w orked it out beforehand) mostly depending onthe thickness of your plastic. Before you charge it right up, though, you w ant to get some of the air out of it. Hook it to an AC source and let it vibrate for a bit, and the oil levelwill drop as the air bubbles out. Top up the oil. Have fun!

Look on laser websites for this design plus pictures. I've also seen baw ls glass bottles used for a capacitor array. (Glass is a very, very good dieletric, but seriously fragile andheavy!) There's lots of stuff out there. Just remember to use a small resistance to stop yourself getting shocked before handling.

May 3rd, 2006, 06:36 PMzajcek01

The car coil is very easy to get, but I personaly like better the TV Flyback transformer with uilt in cascade. The sw itching circuit is made of 555 chip and MOSFET transistor toswitch the current. Transistor needs to be cooled. Then you simply add the capacitor in paralell with the coils output to get the higher current.

I had a shock from that kind of appliance and it threw me across the room under the chair and I woke up cupple of minutes later not remembering exactly what has happened.:D

ps. sorry for my english

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When you go to the reply window , you'll see in the top-right corner an icon that looks like this (http://ww w.roguesci.org/theforum/images/editor/spelling.gif).

Click on it and follow the directions.

Failure to RAPIDLY improve your grammer (i/I failure, for instance) and non-use of spell checking will result in your non-membership ASAP.

NBK

November 25th, 2006, 01:41 PMelectricdetonator

Seems the issue is split all over the place here ;)

Just replied to the cattleprod thread w ith a ASCII schematics for a stungun using a cascade and neon transformer.

But what I'm always missing are the protecting diodes short circuit the inductive parts like the car coils ?

Or do they have build in protection ?

BTW high voltage caps are within every flash light, even in disposable cameras ;)

And w ith a cascade with 6 400 Volt caps u can reach 1,2 kV, make them 12 and you've doubled the fun ;)

High voltage diodes and caps can also be found easily in old TVs and monitors.But be sure you discharge them before handling !

November 27th, 2006, 07:59 PMJacks Complete

a 1.2kV cascade isn't easy. You w ill have to rate all the components in the cascade to the highest voltage found, else it w ill arc over. This becomes an issue as big diodes cost alot more, and high voltage caps of a desent breakdow n voltage are expensive. Buying 12 stages worth w ill cost a lot!

November 28th, 2006, 09:21 AMelectricdetonator

a 1.2kV cascade isn't easy. You w ill have to rate all the components in the cascade to the highest voltage found, else it w ill arc over. This becomes an issue as big diodes cost alot more, and high voltage caps of a desent breakdow n voltage are expensive. Buying 12 stages worth w ill cost a lot!Then main advantage of a Villard cascade is that you'll only need caps and diodes with 2x input voltage, to gain Nx ouput voltage ;)See e.g. here:'http://en.wikipedia.org/w iki/Voltage_multiplier''http://ww w.kronjaeger.com/hv/hv/src/mul/'And just look here for "Hochspannung" 'http://www.fingers-w elt.de/gallerie/eigen/elektro/subversiv/subversiv.htm'With 22 caps and diodes it'll multiply the 90 Volt coming from the self made transformer to 22 x 90 V = 1980 Volt and instead of the used 3 kV caps 200 Volt caps should beenough ;)A nice extra is the last high voltage cap w ith 10 kV and 10nF ;)And high voltage caps aren't so expensive, see e.g. here (again german, sorry):'http://ww w.oppermann-electronic.de/html/keram__hv_c_s.html'100 1 nF 1 kV caps for 6,54 Euro1 10 nF 15 kV cap for 8,50 Euro100 1 kV 1,4 A diodes for 7,67 EuroBut you are right it's not very useful to make a cascade more then ten stages when you want to have current at the end.The usual way to gain higher outputs with less parts is to use a second stage transformer driven by a spark gap / cap resonator.Something like this:'http://ww w.fingers-welt.de/gallerie/eigen/tonne/grille/zuend.pdf'HV is really fascinating ;)

April 16th, 2007, 06:20 PMlamazoid

First of all, hello there!

I'd like to present my work - the result of more than 3 years of stun guns development. This is really pow erful one, circuitry based on taser concept, and it causes any person tofall down immediately, unlike common commercial stun guns, where it takes 5 more seconds for effect to come. Another goal of this project was simplicity and kitchen-basedtechnology, so (i believe ;-) anyone will be able to make it even without electronic experience.Here is the link:http://steelrats.net/readarticle.php?article_id= 119

April 16th, 2007, 07:45 PMevilgecko

Microwaves are very handy for high voltage components. Buy the broken ones for cheap ($1) of online auction site. Each microweave has one 1800-2000V 1uF capacitor and a2500V diode in it. The transformers are worth keeping too although are not suitable for your project.



http://steelrats.net/readarticle.php?article_id=119

The Explosives and Weapons Forum > DIY Engineering > Electronics > Salvaging a large gas discharge lamp starter

View Full Version : Salvaging a large gas discharge lamp starter

March 19th, 2008, 10:31 AMBacon46

I salvaged a high voltage lamp starter from a lithographic “plate burner” where I work. I had no idea what I would do with it but I couldn’t just let them throw it in the trash. Itis designed for rapid start of gas discharge lamps. The links below are to images of the starter, the schematics and the patent. I am hoping to salvage parts off of it to create aheavy duty power supply for chlorate production. I know it is not suitable for chlorate production as it is, but can it be modified or can I salvage certain parts that may be usefulin a power supply for chlorate production?

I am electronically challenged. If the modifications are complex I will do the research on how to make them and get it figured out. I was hoping someone here could shortenthe process and point me in the right direction to start. If I can’t use it for creating a chlorate power supply maybe someone attempting HNO3 production via high voltage arccan use it.

This type of printing plate, one that requires exposure to high intensity light, is being phased out and replaced by a direct computer to plate process. If useful, these thingsshould be fairly easy to come up with. There are many people that specialize in printing equipment salvage and the plate burners are going to be piling up in their warehouses.I also salvaged a nice vacuum pump from the same machine.

Patent 3944876 (http://www.google.com/patents?id=I20-AAAAEBAJ&dq=3944876) Image One (http://img397.imageshack.us/img397/3369/lampstarter001um6.jpg) ImageTwo (http://img397.imageshack.us/img397/381/lampstarter002kd4.jpg) Image Three (http://img214.imageshack.us/img214/1996/lampstarter003gq4.jpg)

March 19th, 2008, 11:10 PMETCS (Ret)

It appears to be an Ignitor/Ballast for a High Intensity Discharge Lamp. Lotta good stuff on it!

It has potential for use in some sort of high voltage circuit or power supply.

The circuitry, as it is, wouldn't be too useful for the application you have in mind. Probably the best sort of power supply for a Chlorate cell would be a used, but still working,computer power supply rated at 350 Watts or more. That would be capable of providing 50 or more Amperes at 5 Volts which would be near ideal, and they are easily modifiedto work outside a computer. Pretty easy to find at Computer Repair Shops or Electronic Salvage Shops.

Do you have any friends who are Electronics Technicians or Ham Radio Operators? They'd be able to quickly evaluate the treasure trove that you have and give you someideas on what it could be used for.

When one is in the right place at the right time it is absolutely amaazing what can be had for free! Way to go Bacon46!

March 19th, 2008, 11:36 PMBacon46

Thanks ETCS

Maybe I will just use it to learn what I can about transformers etc by experimenting with them and un-winding them.

March 21st, 2008, 02:18 PMProdigyChild

The coils in your circuit can easily be used to limit current drawn from your AC line. This is very useful if you want to create high power arcs. Unwinding the coils would benearly as bad as throwing the parts into the trash bin.

As a starting point, buy a bridge rectifier and connect its AC inputs to the AC line with the 'ballast' in series. You have an short-circuit proof power supply and it should be able toproduce arcs. Please connect a varistor of 250V parallel to the rectifier's output to absorb exceedingly high spikes.

Have fun!

March 22nd, 2008, 10:43 AMCharles Owlen Picket

This very useful information for me as I have a powerful lust for Tesla coils. I was really only aware of Microwave and flyback transformers (& associated voltage multipliers)found in older TV's.

High voltage stuff is rare and quite worthy of reclamation in my opinion but just as valuable is sources of same!

March 26th, 2008, 05:19 PMPositron

ProdigyChild has some good advice. They key words being "short-circuit" proof. Current limiting is great to have sometimes.

If you guys want quick & easy high-voltage...go for neon-sign transformers. You can get 2 - 15kV at currents as high as 120mA (0.12 Amps!) from them. Which is a lot at thatvoltage.

Great for Tesla coils.

The newer neon-sign power supplies are all solid-state and pretty much useless. If it doesn't weigh anything...it's useless. You want the old-school core-and-coil tar-filled things; )


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The Explosives and Weapons Forum > DIY Engineering > Electronics > Concepts for chemical reaction monitoring

View Full Version : Concepts for chemical reaction monitoring

March 27th, 2008, 08:48 PMProdigyChild

IntroductionSince a few years electronic sensors emerge on the market that include the complicated steps of transforming the physicalvalue in an easy to use signal.For example: instead of using a thermocouple and having to struggle the really difficult process of amplifying a tiny signalamplitude to usable voltages, calibration, mapping to celsius, one could use an IC like LM75 ( http://www.national.com/ds/LM/LM75.pdf ). This IC is a temperature sensor that can be read out digitally and the result is the celsius temperature.Similar sensors can be found for RGB sensors. These yield an absolute value calibrated at the factory.These sensors are EASY TO USE even for people who are not experts in electronics. Of course there are still analog sensorsthat require much more knowledge in electronics (e.g. MLX93247 thermopiles for remote IR temperature measurement, see:http://www.datasheetarchive.com/search.php?q=MLX90247 ).

Interfacing to a computer opens up endless possibilities, if the computer can control the reaction, too. A separate thread onhow to control chemical reactions by a computer will be the next step provided there's enough interest on this topic.Also, the 'engineers' in this forum will have to provide interface schematics, boards and assembly instructions to let the 'purechemists' take advantage of the electronics. Since I'm more an engineer member than a chemist member and I'm willing todo so this should not be to much a problem ;)

ChallangeMy question to you is:

what sensor to usefor what physical/chemical valueand how it works (theory behind and calculations required)

Example: ph-measurement using color sensors and an pH indicatorpH measurement is possible using special electrodes using a nontrivial amplifier. Too expensive to buy, too difficult tomaintain, too complicated for an amateur to build himself. Why that? Every amateur chemist has determined pH quite a fewtimes, so why not mimic this process?

For example, let's use phenolphthaleine, a preferably green LED and a photodiode. The green LED shines through the solutionunder observation onto the photodiode. Once the pH rises, the phenolphthaleine turns pink and absorbs nearly all of thegreen light and the photodiode 'sees' less intensity.Similarly we can use an easy to use digital RGB sensor like Avago's ADJD-S371-Q999 that can detect color directly inconjunction with a more complex indicator solution.I haven't tried these methods yet, it's just theory. But I can hardly imagine it won't work.

March 28th, 2008, 02:39 AMmegalomania

What exactly do you want to control? Heating/cooling? Reactant addition? Stirring? When a reaction is done? Personally I wasthinking last month I would love to have a webcam set up to monitor a distillation with a motion alarm that goes off whenliquid starts dripping. This beats standing around like a fool literally watching the pot boil (necessary because switching flasksto catch different fractions could happen at any time, but you have to be there when it happens).

I have two temperature controllers now, one free and the other under $30. These are great for controlling other "things"(whatever you can imagine) because they send simple on off signals depending on your temperature preset. I want to useone of mine for an electric furnace to control the temperature. The temp controller controls a solenoid that in turn turns thepower to the furnace on and off. Simple, easy, fun :)

I would say pH meters with computer interfaces are not dreadfully expensive (about $150 at the low end, plenty of usedmodels too) and are well worth the investment if you really need it. There are very inexpensive digital pH meters that couldpossibly be modified to send their output signal to some electronic device that can read the signal. This might take someelectronics know-how, but I imagine there is info available that can translate digits to computers.

Now if you are talking about building some sort of combinatorial synthesizer, that would be a wonderful project. I rather enjoythe concept of microchemical synthesizers, and I think they could be made available very inexpensively if someone bothers todesign such a thing. On the small scale you can achieve very high pressures, high temperatures, use exotic catalysts (cheapwhen you use a tiny amount), get high intensity UV or visible light, and use inexpensive solid state microwave generators andultrasonic emitters. Throw in some peristaltic pumps with solvents and hook up a few cylinders of gasses and one could makejust about anything, albeit in small quantities.

I wrote a short story a few months ago about what the future might be like if microchemical synthesizers become cheap andubiquitous.

My first thought when I read the title was "the cheapest way to monitor the progress of a chemical reaction is to spot some TLCplates." That's not exactly what you mean though.

I have been trying to wrap my head around how to monitor chemical reactions in a microwave. I am still looking for a cheapfiber optic temperature sensor and a microwaveable pressure transducer. The inability to monitor the temperature during amicrowave reaction rather limits the range of experiments that can be adequately performed, and not knowing the pressure ofa sealed vial can be dangerous. If I had 10 grand sitting around I could buy a CEM microwave reactor with all the fancycomputer controls. I refuse to believe these things cost any more than a few hundred dollars to make. I will figure this out oneday.


EDIT: Crap, I can't edit the post title? SIMPLE DATA ACQUISITION INFO ON THE POST AFTER THIS ONE.

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http://www.national.com/ds/LM/

http://www.datasheetarchive.com/search.php?q=MLX90247

ProdigyChild,

I commend you on the great post. Things like this are what we need to help kick off what I think is a great new section on TheForum.

OK. Other than 1). Carbon Dioxide 2). Hydrogen and 3). Carbon Monoxide sensors, I am not familiar with any sensors thatdirectly measure other discrete chemical compounds. There ARE ways to measure anything, it's just a matter of how much timeand money it takes to do it.

Here's a list of some other sensors (a general term) and transducers (a very specific term referring to the direct changing of aprocess into a measurable output.)

Color: As mentioned before, with a source of white-light (LED!) and a single chip, you can convert Red, Green, and Blue light tocorresponding voltages. For those reactions where liquids or gases change color, a chip can tell you exactly what color, and howmuch of it. Could be extremely valuable. And YES, if applied correctly, it will work. 100%.

Oxidation-Reduction-Potential: You guys will know a lot more about this one than I will. I believe these "ORP" transducers(XDCR's) measure the small voltages present on specific electrodes during a chemical reaction.See:http://en.wikipedia.org/wiki/Oxidation_reduction_potentialhttp://en.wikipedia.org/wiki/Table_of_standard_electrode_potentials

Pressure Transducer: As a reaction proceeds within a vessel, the pressure builds up to "X" level at which something can beturned on or off. This also applies to a vacuum. Apply vacuum to a volatile solvent within a vessel, seal the vessel, then watchthe pressure come up (indicated by a voltage) as the substance evaporates.

Optical: As previously mentioned, sensing an amount of light that is present. Shine a laser through a glass reaction vesselonto an optical sensor, to determine the opacity (clarity) of the liquid OR gas inside. If the liquid or gas is luminescent (bio orchemiluminescent) to some degree, measure it!

Temperature: Many Resistor-Temperature-Detectors (RTD's) easily achieve accuracy's of 1/100th of a degree Centigrade.Thermocouples are cheap; the accuracy isn't as good (+/- a couple degrees C), but they have huge ranges.

Gas Sensors: Oxygen and Carbon Dioxide/Nitrogen Dioxide sensors are easy to get. Commonly used in automotive exhaustsystems. Also available are Carbon Monoxide and Hydrogen gas detectors, which simply give an on/off signal if the gas ispresent.

Other Types: Liquid-level, PH, magnetic, infrared, humidity, acceleration, force, etc.

Electrical Conductivity: It may be quite easy to determine relative concentrations of liquid and gas solutions based on howconductive (or resistive) these are to electric current. As an example, pure water (deionized) is an excellent insulator. Add alittle salt, and you can turn on a light bulb through it! The current (Microamps, Milliamps, Amps) tells how much salt has beenadded. Keep the measurement time reasonably fast to avoid the effects of electrolysis. :cool:


Hi All,

For those that don't know, getting data from sources and storing this information to a computer, is referred to as DataAcquisition, or DAQ. The "data sources" can be volt-meters, current-meters, temperature probes, pressure sensors, etc.

I wanted to mention a product from a company called Dataq (dataq.com). For a grand total of 25 bucks, you can record fouranalog voltages that span between -10V and +10V to a file on a computer. The file can be imported to Excel if you wish, butthe included software for the unit is quite excellent. $25.00 gets you the four analog inputs (at a "recording speed" of 240data points per second), and a Serial-Port interface.

You WILL need to convert the output of the sensor to a voltage that the DAQ unit can read. The software creates a graph onthe screen that is scaled with -10V at the bottom, and +10V at the top. Yes, the graph can be scaled to a smaller voltagewindow, but you'll lose resolution (it will get blocky).

I am not affiliated with Dataq in any way, other than that I'm an extremely pleased customer. I recently tried out their "DI-148U" USB DAQ unit for $50.00. It can record eight voltages, simultaneously, at 240Hz. My new laptop doesn't have a serialport, so I had to spend the whopping extra $25.00 to go to USB connectivity :).

Anyhow, 240 samples per second is PLENTY fast enough for most chemical reactions (ignoring detonations :D). A trick thatDataq uses to make its money, is that they have some extra software that will allow recording at data-rates of up to 14,400samples per second :cool:

Truly great products. Just wanted to mention it.

March 29th, 2008, 08:40 AMmegalomania

That Dataq equipment is much cheaper than the products at Omega.com, of course Omega has some very sophisticateddevices. I see today they are hawking a Wireless Sensor System Web-Based Monitoring, http://www.omega.com/ppt/pptsc.asp?ref=zSeries, starting at $95. I was looking for some optical temperature measuring systems, and now I know theycost over $2000 not including accessories like the IR probes.

I saw a journal article last year about using real time NMR sampling to plot the course of a reaction. I can't even begin tofathom how they continuously and automatically run samples through a NMR and evaluate the spectra in real time. NMRaccessories are expensive as it is, this setup must cost a fortune. I have seen GCMS systems that continually sample areaction, this is much easier to do since samples can be directly injected into the GC.

This time of sampling makes me wonder if there is some sort of testing methods that could be conducted on extracts of areaction. Perhaps chemical additives that cause color changes or alter conductivity depending on the presence or concentrationof a desired compound. Such reactions would be undesirable in the reaction flask, but on samples it would be fine. Smallsample sizes might make it easier to use optical measurements.


http://en.wikipedia.org/wiki/Oxidation_reduction_potential

http://en.wikipedia.org/wiki/Table_of_standard_electrode_potentials

http://www.omega.com/ppt/

I think, at least for organic reactions, that most forms of reaction monitoring beyond temperature control is rather useless.There are very few reactions on the lab scale where pressure, pH, conductivity, etc. are useful or measurable. How useful is itreally to have an optical instrument? I actually can't think of one reaction where that would be useful. There are reactions thatchange color, sure, but that is in no way indicative of the completion of the reaction. If you pour through the literature you willobserve almost exclusively that chemical reactions are evaluated by time and temperature.

What I would like to see is a schematic of how a thermocouple based temperature sensor can control the power levels of amicrowave. Microwave reactions do not work well with the domestic microwave method of pulsing the microwaves from full blaston to off. Domestic microwaves with adjustable "power levels" actually turn the magnetron rapidly on and off, and lower levelsmerely keep it off slightly longer, but it still outputs 100% power when on. Since the chemical reactions tend to ceasecompletely when the microwaves cycle to off, and to react too fast when on, laboratory microwaves always stay on, but changethe outputted wattage.

I am trying to figure out how a temperature controller can decrease the power to a magnetron without shutting it off. Thisseems a bit trickier, at least to my limited electronics experience, than simply turning the thing off completely.


About a year ago, I've disassambled an old microwave oven and could not resist to power the magnetron a 'little bit'.

It turned out that - YES - such a conventional magnetron can emit less than full power provided you simply don't give it fullvoltage/current :)

The biggest problem (to me at that time) was the heating of the cathode. It runs at 3.4V and approx 12A. The anode needskilovolts.

I can see 2 possibilities of power control.

1. Lower anode voltage / current.This requires modifying the high voltage supply or even build one from scratch. Probably not everybodies deepest desire.

2. Reduce cathode heating.Simply use the HV from the original oven, but put a low resistance potentiometer in series with the heating. Be careful as theanode is grouded and the cathode is actually highly negative with respect to ground. That means the potentiometer is at HIGHVOLTAGE. Since the resistance of the cathode heating is about 0.25 ohms it won't be too difficult to improvise such apotentiometer using a steel wire.

However, Mega, do not expect the output of such a contruction to be constant power. It will be modulated by the 60Hz of theAC line because the circuit is too simple.If constant power is required then only a good, adjustable high voltage supply (up to 5kV) will do the job. Up to 1000V is quitestraight forward. DC voltages above require more uncommon diodes or cascading techniques.

Electronic Power controlLet's assume we use cathode heating power control. In order to avoid using opto-couplers (5kV ones!) we ground the cathodeand put 5000V on the case of the magnetron. Don't touch any more any casing ;)Now connect the schematic attached to be able to control the magnetrons heating with a DC input voltage. This was the difficultpart.

I used to use the AD597 IC to amplify the thermocouple voltage.

Another OPV will be necessary to compare the current temperature to the set-point temperature and generate a useful powercontrol voltage.Also some dampening must be implemented to avoid temperature oscillations. This depends on the reaction vesselproperties.

March 29th, 2008, 09:08 PMmegalomania

Modifying the ove n for constant ou tput has alre ady been so lved by Stefan Binder at the Art n Electronics website some yearsago. He has a page up about converting domestic microwave ovens athttp://stefanbinder.privat.t-online.de/uW.htm

I bought this broken microwave oven cheap at a flea market (high voltage capacitor was shorted). After replacing the capacitorI put a burning toothpick into the oven to produce those cool ball lightning-like plasmoids. Didn't work too well - I rarelymanaged to produce any plasmoids. I think it's because of the low oven power (500W).But putting evacuated vessels (light bulbs, fluorescent tubes, old HeNe lasers) inside the oven cavity worked nicely - exceptthat now 500W was too much power and the vessels melted very fast. So I decided to make the oven power adjustable. Themicrowave oven's own power selector doesn't work as it just turns the magnetron on and off for variable amounts of time(some seconds). The food with its high thermal capacity doesn't mind, but this way of power reduction is not suitable forplasmas. The easiest thing would have been to simply connect the microwave oven transformer (MOT) to a variac. But this wayI would not only have adjusted the cathode voltage but the heating voltage, thus the filament temperature, as well. So I keptthe original MOT to heat the filament and used my 4 MOT power supply for the cathode voltage. This solution has anotheradvantage - instead of the original half wave doubler the magnetron is now powered by the full wave rectified output of thefour MOTs - which makes the plasma more stable. Of course when powering the magnetron with 4kV now, power is muchhigher than before, but because of the robust construction of magnetrons this shouldn't do much harm for short periods oftime - as long as it doesn't melt.

The site does not exactly include schematics, but it has pictures of the thing. I wonder if connecting 4 transformers might be alittle overkill. I am not exactly familiar with what having so much extra voltage would do to the microwave output, does thehigh voltage help it run constantly, or does it actually increase the wattage of the magnetron?

I think automatically controlling the power output of the magnetron might be somewhat difficult, at least from my perspective,but a simpler method would be to manually adjust the power until an equilibrium state of a chemical reaction is achieved. Likea variac control knob, the power can be dialed down while watching a temperature meter to regulate the heating of a reaction.A big problem with microwave chemical reactions is at full blast it just gets hotter and hotter, so being able to control the powerto moderate a reaction is a very important feature.

The hideously expensive CEM systems use microprocessor controlled temperature measurement and power output control to


http://stefanbinder.privat.t-online.de/uW.htm

sustain a reaction at a set point temperature. I imagine the microprocessor calculates some Fourier wave equation by rapidlyraising and lowering the power until a steady temperature is achieved.

My unmodified domestic microwave demonstrates very clearly why these things are unsuitable for some experiments. I had areaction constantly boil over because the wattage is just too high. Dialing down the power to a defrost setting just means thereaction goes from dead to boil over as it turns off and on. I don't want the microwave to stop emitting microwaves, and I onlywant full power during the initial stages of heating from room temperature where the dielectric loss factor is lower. Since thetan delta of a reaction is temperature dependent, less and less power should be applied to level off the rate of heating.

While I am sure a system could be made to regulate the power automatically, the nature of microwave chemical reactions,especially in a modified domestic microwave oven, means it should be watched like a hawk. Best to have a manual powercontrol knob just like regulating the power of a heating mantle while watching the thermometer in an ordinary reaction.

March 29th, 2008, 10:10 PMBlackFalcoN

I think the key for achieving such a device is to replace the controller part of the microwave.

The way most microwave ovens work is by varying their duty cycle according to the power setting. This means that the "defrostsetting" for example, will run the cavity magnetron element on full power(100% voltage) for 10 seconds, then do nothing for10 seconds (0% voltage), then repeat the cycle, until the count down timer runs out.This method is called Pulse Width Modulation (PWM) and works with a square (block) wave signal. The standard controlcircuitry works great for defrosting food, since food is not very critical about it's temperature. Therefor the basic power settingsuse a long period for enabling/disabling the magnetron (10 secs - 15 sec - ... )

Cavity magnetrons are not designed to run efficiently on a different voltage that they were designed for. They need a fixedhigh voltage to work efficiently.

So instead of changing the amplitude (voltage) of your signal, you alter the frequency of the current signal. The averageoutput will be the smouthed out result ofa series of high and low pulses.

The duty cycle of a signal is the ratio between the 'uptime' of the signal compared to the 'total time' of 1 period of the signal.For example, if you have a PWM with a duty cycle of 75% @ 5000 Volts, then the average voltage of 1 period of the signal =3750 Volts.( 75% of the time @ 5000 V, 25% of the time @ 0 V ). 0 through 5000 Volts can be achieved by just varying the duty cycle for0 to 100% while never altering the top voltage of your square signal.

Look at the attached image for a graphical aid for understanding PWM.

What you want to do to achieve a much more precise temperature control, is replace the control circuitry that translates yourselected power setting on the microwave oven, into a PWM signal. ( since even the lowest power setting changes too slow toachieve the desired level of control )

All that is really needed to design your own much more precise control unit to switch the magnetron on/off is a micro controllerthat will generate a new digital PWM signal, a power transistor or HV relay to switch the high voltage circuit (since you can't justhook up the 5V logic from the microcontroller to a kV appliance ;) ) and a potentiometer that will read a variable analog valueselected by the user to represent a certain power setting

It's not very expensive either:25$ for an Atmel168 Board (you don't want to design your own PCB and solder the whole thing, flash bootloaders intoEEPROMs and design a programmer when you can buy a fully assembled unit that works straight out of the box via USB forunder 25$.)

Look into the 'Arduino Diecimila', which is an open source project based around the powerful Atmel mega168 MCU and isdesigned for amateur developers with a very easy and user friendly programming language. It can even be programmed innative C for more experienced power users.And it is a one time purchase, since one microcontroller can be easily used in other projects as well.

A salvaged power transistor and a cheap variable resistor can be literally had for pennies.

Heck, you could even hook a cheap analog thermistor to your micro controller, and let the whole thing run on automatic if youdesire.The microcontroller probes the thermistor a couple of times a seconds, and changes the output of the magnetron accordingly.

I never done this in practise, so is there anything about my design that would not work according to other members ?

EDIT:Not really sure, but you probably also might want to add additional cooling for your cavity magnetron element if you intend torun it at a duty cycle of 100% for extended periods, since they will heat up internally too, but were never designed to run atthat setting.


Most likely, there is a certain threshold of voltage that is required to compensate the intrinsic losses of the magnetron tube.Once the input voltage is slightly above this threshold the oscillation builds up and some RF is emitted although at a terribleefficiency close to zero. But this is not Mega's problem (the efficiency at low output powers) - he simply wants a way to reducepower. It's not that bad if the magnetron is inefficient.

On the other hand, if varying anode voltage was inefficient then all domestic microwave ovens were inefficient. Their anodevoltage varies sinusoidal from 0 up to 5000V and down to zero again. Varying anode voltage is the typical usage! At least withthe one diode voltage doubler supply found in the 3 ovens I've opened so far and in Stefan Binder's .

My electronic suggestion was to tune the cathode's emmision of electrons and keep the voltage high. Adjusting the cathodesheating power in the schematic is done with PWM at a frequency well above the heatings reaction time (seconds).

Stefan Binder's solution provides a more stable HV supply providing 100Hz ripple instead of 50Hz and the possibility of furthersmoothing using a capacitor.This can be beneficial if oscillations of 50Hz/60Hz are not tolarable for a chemical reaction. However, I can't believe that 50Hz


(=20ms) are too slow.

If someone suggest using a microcontroller for control tasks then I say YES!As to the type of controller I'm hooked on the ARM7 LPC2000 types (NXP). Don't like the Atmel parts neither ATmega norSAM7. Too f...ing much of code needed to enter the main() for the SAM7, really. PLL, clock distribution,....

March 30th, 2008, 10:11 PMmegalomania

I was just reading about the Arduino and its group of open source modders yesterday at Daily DIY, what a coincidence. Ifthese are that cheap, perhaps some automatic control could be devised after all.

Indeed modifying a microwave in certain ways does require additional cooling of the magnetron. At the very least a strongerforced air cooling fan, and at the extreme end water cooling of the fins similar to water cooling blocks used in computers.

One of the benefits of monomode microwave reactors is a much more intense microwave field with less wattage. If the field istuned right, and the sample is precisely positioned at a node, a 100-300 watt magnetron is more than sufficient. I believe therule of thumb is a monomode microwave is 4 times as power as a multimode microwave.

If I could figure out what the dimensions are of the CEM corp monomode research microwave reactors that use self tuningcircular waveguides, I would much prefer to build something like that. Their patents include schematics, but no measurements.The design is very simple, just a central cylindrical cavity irradiated by 7 vertical slits in the inner wall of a cylindrical waveguidethat makes a 360 but the end is closed off. The hard part is the height and radius of the wave guide must be exact to sustaina monomode field. The height, width, and spacing of the slits must also be very precisely placed.

I have a caliper, and I know where there is a CEM Benchtop... I just need a little quality alone time with the thing :)

April 1st, 2008, 02:21 PMPositron

1. If the microwave isn't powerful enough...I'd recommend buying a bigger microwave. How fast do you want to raise thetemperature? Pawn shops have more of these things than they know what to do with...kilowatts too...

2. Cutting slits, tuning waveguides, making antennas...is probably more complicated than necessary for this application.Sounds like redesigning the wheel to me, but I haven't read all of the posts.

3. BlackFalcon had it right with the PWM theory, except that I think that two chips from Radio Shack could be used to generatethe ON/OFF signal instead of a microcontroller. I'd use an NE555 in astable-multivibrator mode to produce a triangle wavethat's about 1Hz (peaks on the waveform are one second apart) in frequency. Then, take the triangle off of pins 6 and 7, andcompare this with a variable DC voltage that's created off the power supply with a small PC-board-mount potentiometer. Use aslow op-amp to do the comparing...LM741, LM358, TL082, TL072 are common part numbers. Internet search terms: 555 PWMgenerator, PWM signal generator, PWM circuit, triangle wave PWM. The entire circuit could literally be built with parts fromRadio Shack.

---------------

I think that the solution to this entire problem would be to use an off-the-shelf temperature controller.

Type in Temperature Controller on Ebay and you'll see what I'm talking about.

Slap a thermocouple on its input, and slap a relay on it's output (it may already have one internally) to control power to thehigh voltage transformer that powers microwave. Inside the microwave, connect the primary-side (120 or 240VAC) to the mainsvoltage, running one leg THROUGH the relay on the output of the process controller. That way, the controller in the microwaveis completely bypassed. If you've got it right, shorting the wires that go to the relay together will turn the magnetron on.

Once finished, you use buttons to tell the controller what temperature to hold the reaction at, and it regulates it there.

Ex. the controller says "shit...the temp's too low", so it clicks the relay on, powering up them maggie, getting the chem'shotter.

Controller says "shit, the temp's too high", it clicks the relay off, cutting power to the maggie, so the reaction cools off.

Most controllers will click the relay once per second or so, but in this case it's irrelevant.

These controllers are capable of regulating the temperature of the reaction within a couple of degrees or better.

The relay contacts need to handle the current that powers the microwave. A 240VAC 20-amp relay will do the trick.

You'll need to work out how to get the thermocouple inside the microwave cavity without bringing the radiation back out to theoutside World. I'd run the thermocouple into a 100% sealed copper tube (1/4" refrigerator tubing, or small brass tubing) thatdips down into the solution you're trying to heat. Solder it all the way around the wall of the oven where it enters. Use a 150Wiron and paste flux (C-flux is awesome from hardware store).

April 1st, 2008, 07:42 PMmegalomania

No, just using a temperature controller is not a solution, as I wrote earlier in this thread. These reactions need to be constantlyexposed to microwaves to maintain the reaction rate. I would say the simplest way would be to manually dial down the powerto achieve the right temperature.

Since the dielectric loss factor of a material increases with temperature (the hotter a material gets, the more microwaves itabsorbs) some materials need to be hit with higher power at room temperature, and then gradually get less and less power.

Having a temperature controller turn a microwave on and off is no different than what a domestic microwave does now. If youset the power level of a microwave to 50% it stays on half the time, and is off half the time. Your reaction goes from frothingout of control to no reaction at all.

For better temperature control you need to be able to fine tune the power output to suit the sample and sample size. A rapidon and off cycle just spikes the temperature and plummets the temperature. Worse yet, a microwave transparent solventmight stay at a high temperature for several minutes, and the temp controller will keep it off, but during this time the reaction


is not happening because it depends on microwave energy to initiate it.

The best microwaveable thermocouples are supposed to be aluminum shielded probes that make a grounding connection tothe metal shell of the microwave oven. I have not yet found where to get such a probe. The important part is to ground theprobe to prevent arcing, which gives false temperature readings. My parents once had a microwave back in the 80's that had aplug in temp probe for checking the internal temperature of something like a turkey or other large meat item. Who cooks aturkey in a microwave anyway? I remember wondering how could this work since it is metal. The walls of a microwave are metaltoo, but they are all grounded.

Building waveguides and tuning them is an extremely difficult engineering challenge made worse by the fact the companieswho build such things keep their cards close to their chests concerning the details. The CEM waveguide though is puresimplicity, it is self tuning just by being round, it is just thin sheet metal spot welded together. It's just that the height, width,radius, etc. of the metal has to be exact because of the nature of microwaves at a wavelength of 2.45 GHz. I could spendyears running simulations in CST Studio Suite, or I can spend 5 minutes measuring the real thing.

There is a picture in US patent 6607920 (figure 4 and 5) that shows what the waveguide looks like. There is not much to it,they just left out the dimensions. This is like having a new car without the keys...

April 3rd, 2008, 03:58 AMPositron

No, just using a temperature controller is not a solution, as I wrote earlier in this thread. These reactions need to be constantlyexposed to microwaves to maintain the reaction rate. I would say the simplest way would be to manually dial down the powerto achieve the right temperature.

If I'm understanding you correctly, what you're saying is that the reaction needs the application of low-power microwaves 100%of the time, and that something other than temperature information is needed to control the reaction. Perhaps that"something" is the crazy microscopic analysis (PET) thing that you mentioned earlier.

But, you did say it. You said that the simplest way would be to manually dial down the power to achieve the right temperature.By saying that, you implied that a human would be dialing down the power until the human was satisfied with the temperature.Therefore, I believe you implied that the reaction could be controlled by the temperature.

I guess that's why I still (sort of, now?!) think that a temperature controller would be the solution, because a temperaturecontroller is capable of maintaining the temperature of a reaction to better than .001 degree C, even if the reaction itself isexothermic or endothermic.

1. A microwave oven's internal temperature control circuit can't do that.2. A human can't do that.3. A specifically-designed temperature controller would be the right tool for the job.

Worse yet, a microwave transparent solvent might stay at a high temperature for several minutes, and the temp controller willkeep it off, but during this time the reaction is not happening because it depends on microwave energy to initiate it.

Yep, from what you're saying, it sounds like temperature information alone is not enough to be able to properly control thereaction. If this is the case, then all bets are off for the temperature controller's capability of fully controlling the reaction.Which means that I am/was wrong about it being a solution to the problem. My apologies if this turns out to be the case.

For better temperature control you need to be able to fine tune the power output to suit the sample and sample size.

Yes, industrial temperature controllers will fine tune the power output to suit the sample and size.

Having a temperature controller turn a microwave on and off is no different than what a domestic microwave does now.

There is a huge difference between the shitty temperature control circuit in a microwave oven (that doesn't even havetemperature feedback!!!) and a specifically-designed temperature controller. At least in my microwave oven, there isn't athermocouple, RTD, or thermistor...

A rapid on and off cycle just spikes the temperature and plummets the temperature.

The rapid application of on/off cycles is a good thing. It's when the application is too slow (such as in a microwave oven) thatthe thermal mass of the sample can't filter or average or smooth out the temperature changes. The result is temperatureripple.

If the thermal mass of the substance to be heated is very low, then the frequency of that application of energy will need to beincreased to decrease the temperature ripple.

The best microwaveable thermocouples are supposed to be aluminum shielded probes that make a grounding connection tothe metal shell of the microwave oven.

Anything that isn't microwaveable, can be made microwaveable by placing it inside of a faraday cage.

A "microwaveable thermocouple" is just a normal thermocouple stuck inside of a metal tube that is connected...I mean reallyfucking connected on all sides with no gaps...to the enclosure of the microwave cavity where it enters.

I have not yet found where to get such a probe.

www.omega.com has some pre-shielded thermocouples, but it's a lot easier and a lot less expensive to just buy some cheapones and run them into your own copper tube. Copper is easy to solder. The stainless steel normally used to shieldthermocouples isn't so easy to solder.

The important part is to ground the probe to prevent arcing, which gives false temperature readings.

Not grounding (a better word would be shielding) any wires or probes entering a microwave cavity will do several things. It willnot only add a ton of noise to the measurement, but it can (and probably will) straight up fry the inputs to the circuit from theridiculously high voltage coupled onto the wires from the electric field inside the oven. At the same time, it will probably re-radiate the 2.4Ghz out into the free space around the wires until the oven is turned off.

April 3rd, 2008, 10:06 AMBlackFalcoN


BlackFalcon had it right with the PWM theory, except that I think that two chips from Radio Shack could be used to generatethe ON/OFF signal instead of a microcontroller.

That's very true, soldering your own dedicated controller would probably be cheaper, but you have to take into account that theaverage chemical engineer/scientist is not an electronics specialist, and a microcontroller allows for very easy additions of extrasensors later.

Also, for 25$, do you really want to spend hours and hours figuring out how to design, assemble, solder and make the PCB ?

The Arduino MCU I mentioned also allows for very easy communication with a PC, so external control and monitoring from anetwork, or extensive logging of sensory output to a PC logfile are easy to do.

Also, the MCU can be used in different generations of microwave designs, where as Radio Shack components are prettypermanent once you have soldered them.

If you are absolutely confident in your electronic skills, and have performed all the calculations in advance, then I agree,Radio Shack items is the way to go since your project will be somewhat cheaper + you don't have to program any IC's.

If you have an open-ended project, that will grow with time and you want to keep tweaking and adding additional modules toit, go with a MCU.

April 4th, 2008, 05:33 PMmegalomania

A manually controlled microwave power output would work the same as a heating mantle. You can crank a heating mantle upto 70-90 in the beginning to heat up a flask faster, then lower it to about 40 while the reaction starts, and gradually fiddle withthe power knob to maintain the desired temperature. Because many materials being microwaved tend to absorb moremicrowaves the hotter they get, the ability to dial down the power would be of great benefit to sustain a steady temperature.

Some, not all, reactions do require a continual application of microwave energy to sustain them. Many reactions conducted inthe microwave do just depend on heat, as comparative experiments using convection heating has shown. Temperature controlis still very important because some compounds decompose at elevated temperatures, and some undesirable side reactions.

There is no need for some other type of a sensor to monitor the reaction, just temperature control.

I would think with a better explanation of what kinds of chemical reactions are possible in a microwave, the problem could besolved easier.

1) Microwave reactions identical to convection heating (heating mantle). These reactions work just by applying heat.Temperature control is important to maintain a temperature within a range. This is like boiling a cup of water on the stove, orin the microwave.

2) Microwave reactions in a quenched environment. Using a nonpolar solvent that is transparent to microwaves means areaction can happen by being zapped with the high energy of microwaves, but will immediately be cooled by the solvent.Another form of this is forcing a stream of gas into the reaction mix to keep it cool. Reactions of this type might involvemetallic catalysts that superheat because of arcing, but on the microscopic scale, and the superheating lasts a very tinyfraction of a second.

3) Microwaved reactions in a sealed container. As the temperature rises, so does the pressure, and if the temperature gets toohigh the container could burst. This is where a pressure sensor would be of great benefit, but that is largely a safetymechanism to scram the microwave after crossing a dangerous threshold. By controlling the temperature, the pressure canstay within acceptable limits since temprature and pressure are related.

4) Microwave effect reactions. The still mysterious application of microwave energy that seems to enable some reactions tohappen only when exposed to microwave radiation. These reactions are not reproducible with convection heating, nor when allother factors are equal.

One very important factor that gives microwave reactors an advantage is the decrease of time to run a reaction. This effectrequires a constant application of microwave energy for some as yet undetermined reason. It is for this reason I do not want amicrowave that pulses on and off. Once your microwave shuts off the reaction is little more than a convection heated reaction.The ability to reduce microwave power output to a minimal level is invaluable.

Trust me when I say this: It is unacceptable for the microwave to cycle on and off; it must decrease its power output instead.

How would you sustain water at a slow boil inside a microwave without it boiling over? You can set it on high for the first fewminutes until it starts to boil, but if you reset the microwave to 50% you will notice it goes from boiling over to not boiling atall.

There is a reason chemists no longer use unmodified domestic microwave ovens. There is a reason the expensive laboratorymicrowave reactors all have adjustable power outputs. There is a reason these microwaves emit microwaves continually, notpulsed on and off.

A regular thermocouple, like those at Omega, can be used, but it still needs to be modified. Grounded is the proper wordbecause that's the word used in the scientific literature that tested and evaluated the best microwaveable thermocouple. Thereis a big debate right now about using thermocouples, but I don't plan on doing any high level pharma research in a modifiedmicrowave to where it would matter. For whatever reason, using aluminum as the sheath gives truer temperature readings. Thepurpose of grounding the thermocouple to the microwave cavity is to give the electric current that builds up in thethermocouple sheath some place to go other than arcing to the thermocouple.

Evaluation of shielded thermocouples for measuring temperature of foods in a microwave oven.RAMASWAMY H. S. (1) ; RAUBER J. M. (1) ; RAGHAVAN G. S. V. (2) ; VAN DE VOORT F. R. (1)Journal of food science and technology, 1998, vol. 35, no 4, pp. 325-329.

Flurorptic techniques are normally used for measuring temperatures in a microwave environment because thermocouples havebeen generally assumed to cause electrical perturbations and arcing inside a microwave oven. However, shielding of thethermocouple junction in an aluminium tube grounded to the microwave cavity wall has been reported to prevent electricalperturbations and permit measurement of temperatures. Shield heating was reported to be the main cause of error. In thisstudy, several shielded thermocouples were evaluated for temperature measurement inside a microwave cavity and comparedwith a standard fibre optic temperature sensor. Results indicate that thermocouples can be used for temperaturemeasurement in microwave ovens and shield heating, a common problem associated with these probes, can be by proper


design (shield isolation and body insulation) to yield reasonably accurate values of temperatures (errors <2°C). The probescan be effectively used to monitor/measure temperature of food products during microwave heating.

Temperature Measurements during Microwave Processing: The Significance of Thermocouple Effects.Journal of the American Ceramic Society, Volume 84 Issue 9 Page 1981-1986, September 2001.

Reliable and accurate temperature measurement during microwave processing of ceramic bodies is controversial. Althoughthermocouples are routinely used in conventional thermal furnaces, their presence in microwave furnaces can locally distort theelectromagnetic field, conduct heat away from the sample, induce thermal instabilities and microwave breakdown, and lead toserious measurement errors. These thermocouple effects have been studied and found to be more pronounced in low- andmedium-loss ceramic materials. To decrease the thermocouple effects during the processing of advanced ceramic materials,an optical, noncontact temperature sensing system has been developed, calibrated, and incorporated into a computer-controlled microwave furnace.

Microwave irradiation of wood packing material to destroy the Asian longhorned beetle.Fleming, Mary R. ; Hoover, Kelli ; Janowiak, John J. ; Fang, Yi ; Wang, Xin ; Liu, Wenmin ; Wang, Yuejin ; Hang, Xiaoxi ;Agrawal, Dinesh ; Mastro, Victor C. ; Lance, David R. ; Shield, Jeffrey E. ; Roy, RustumForest Products Journal, 1-JAN-03

Due to equipment malfunction, two different multi-mode microwave ovens with non-uniform field distributions were used forthe microwave temperature gradient experiments. The 2.45-GHz Panasonic oven (model 4 NNL728BA) is 120 V AC/60 Hz with1580 W of input power and 1000 w of power output. The oven was modified with a Powerstat Variable Transformer (Type3PN117C: input 120 V, output 0 to 120 V, 12A). The second oven was a 2.45-GHz Amana Radar Range (model #RR4DW) withan output power of 1600W. The oven was modified with an Adjust-A-Volt Variable Transformer (output 0 to 120 V). In bothsetups, three k-type thermocouple wires were threaded through small holes on the side of the microwave. A thin layer ofaluminum metal tape was wrapped around each wire and around the welded tip. The wires were grounded by taping the wiresto the metal inner chamber walls with aluminum tape. Each thermocouple was connected to an Omega silver-plated selectorswitch (model #SW142-6-B: 2 pole, 1/2 din). A K-type compensating lead connected the switch to the Omega Digitalthermometer (model #2168A). Both of these systems were tested for radiation leakage with a Rahman Radiation meter Model#48lB and a Rahman Probe Model #82 manufactured by General Microwave Corp. In addition, a simple boiling water test wasperformed to check the accuracy of the thermocouples. The thermocouple tips were placed in a beaker of water and themicrowave was turned on. A temperature reading of 98[degrees]C was recorded when the water began to boil in the Panasonicsystem and 99[degrees]C in the Amana System. This was deemed acceptable.

To test the potential of a loss of sensitivity with aluminum foil/tape shields on the thermocouple readings, one shielded andone bare thermocouple were placed close together in a Kanthal heating coil fumace. The oven was ramped to 400[degrees]Cin 8 minutes. Readings were taken every 15 seconds. In all cases, the shielded thermocouples were the same or lowertemperatures than the bare thermocouples. At temperatures lower than 100[degrees]C, the shielded thermocouple lagged by0[degrees] to 4[degrees]C. Between 100[degrees] and 200[degrees]C, the shielded thermocouple lagged by 8[degrees] to16[degrees]C. From the results of this experiment, we can assume that temperatures recorded during the microwaveexperiments are accurate at temperatures under 100[degrees]C, but are likely understated at temperatures over100[degrees]C.

Irradiation of the ALB in China

A common kitchen multi-mode microwave oven with a non-uniform field distribution (Galanz model #WD900) was used in allexperiments conducted in Hohhut, China. The input was 1400 kW and output 900 kW The oven was modified by splicing aPowerstat Variable Transformer (Type 226: input 240 V, output 0 to 240 V, 7.5 amps, 50/60 frequency) into the main powercord (Fig. 1). In addition, three type k thermocouple wires were threaded through the grating on the side of the microwave. Athin layer of aluminum metal tape was wrapped around each wire and around the welded tip. Since the inner microwavechamber was aluminum metal, the thermocouple wires were grounded with aluminum tape to the inner chamber walls. Eachthermocouple was connected to an Omega silver-plated selector switch (model #SW 142-6-B: 2 pole, 1/2 din). A type kcompensating lead connected the switch to the hand-held Omega thermocouple read-out (model #HH-26K: type k, -80[degrees] to 482[degrees]C). A Holladay Industries microwave leakage meter (model #HI1501: 0.1 to 100 mW/[cm.sup.2]at 2450 MHz) was used to test the microwave set-up for radiation leaks. The simple boiling water test as described for the U.S.experiments showed an acceptable temperature reading of 98[degrees]C.

The reliability of thermocouples in microwave ceramics processing.

It is not rare to hear arguments against the use of thermocouples for taking temperatures in processes that are taking placeunder microwave fields. However, the simplicity of this device makes it attractive to consider its use. One question that ariseswhen thermocouples are employed is whether the electric field perturbs the measurement, and if the thermocouple affects theprocessing. The process that was chosen for conducting this test was the synthesis of spinel (MgAl2O4) using microwaves as apower supply and hematite (Fe2O3) as an additive for both spinel formation promotion and susceptor. The alumina-basedsystems are very important to study because this is one of the most common ingredients in refractory materials. There aremany discussions about the improvement of the process when microwaves are used, but a kinetic comparison cannot beperformed if the temperature is unknown, and that is the reason for emphasizing the measurement techniques. The analysisof the obtained samples was carried out by X-ray diffraction of powders. The results of this work show that there is nodifference between the products obtained when the thermocouple was inserted in the system, compared to processing withoutit; hence the thermocouple is appropriate for this application.

Combined effect of microwave and activated carbon on the remediation of polychlorinated biphenyl-contaminated soil.Xitao Liu, Gang YuChemosphere, Vol: 63 Issue: 2, April, 2006, 228-235.

The temperature measurement in microwave field is regarded crucial for reactions. Some researchers ( Cuccurullo et al., 2002)believe that traditional technique of thermocouples for temperature measurements cannot be applied inside microwave ovensdue to the electromagnetic field and the metal probes interactions, while there are reports that a thermocouple introducednormal to the direction of the electromagnetic field does not influence the electromagnetic field distribution (Liu et al., 1994;Roussy et al., 1995 [ Liu et al., 1994, Roussy et al., 1995]). Menéndez et al. (1999) compared an Inconel sheltered type-Kthermocouple and an infrared pyrometer in measuring the temperature of carbon bed during microwave treatment and foundthat the obtained results for these two techniques were comparable. According to their method, the temperature profiles ofsoil/GAC mixture in microwave field under different microwave power, GAC amount added, soil mass and moisture content,were recorded by a sheltered type-K thermocouple.

Effect of microwave power

Besides the nature of the material (dielectric properties) being treated, the temperature attained in microwave irradiationdepends as well as on the microwave power applied to the sample. The majority of the absorbed microwave power is convertedto heat within the material as


(1)http://img177.imageshack.us/img177/8885/si1fh8.gif

where E is the magnitude of the internal electric field, is the relative effective dielectric factor, ε0 is the permittivity of freespace, f is the microwave frequency, T is the temperature, t is the time, ρ is the density, and Cp is the heat capacity ( Clark etal., 2000).

For a given material, the temperature can in principle, be modified by adjusting the input power ( Menéndez et al., 1999). Onespecial point to be noted is that the power levels used here are continuous, not just timed mark/space ratio control. Theinvestigated power series was 300, 500 and 700 W. For 20 g of soil, GAC added and water content involved were 1.0 g and0.54%, respectively.

Thermal Treatment of Active Carbons: A Comparison Between Microwave and Electrical Heating.J. A. Menéndez, E A Menéndez, A. García, J. B. Parry and J. J. PisJournal of Microwave Power and Electromagnetic Energy, vol 34 iss 3, 1999 pg 137-143

Two commercial activated carbons were subjected to thermal treatment in a N2 atmosphere using a microwave multimoderesonant cavity and a conventional electric tube furnace as heat sources. The temperature of the carbon bed during themicrowave treatment was monitored using an infrared pyrometer and an Inconel sheltered type-K thermocouple. A comparisonbetween both methods of measuring temperature was made. When similar treatment temperatures are used, both techniquesproduce similar changes in the textural and chemical properties of the activated carbons. However microwave treatment ismuch less time-consuming than conventional heating. Microwave treatment in an inert environment seems to be an efficientand attractive way of removing oxygenated functionalities from carbon surfaces and of increasing the hydrophobicity andbasicity of carbons.

I have dozens more references on modifying domestic microwaves for laboratory use. I am not spouting theory when I makemy statements on modifying a microwave, all my information comes from published sources who have actually built and usedmodified domestic microwaves in their research. The only problem is these people are a little thin on exactly HOW theymodified their microwaves. Therefore I know what I want accomplished, it's just a matter of figuring out the specifics.

April 5th, 2008, 03:52 AMETCS (Ret)

Magnetrons can be operated in the Continuous Wave Mode by applying well regulated D.C. to the Cathode (Anode is typicallyat Ground Potential).

An adjustable power supply capable of delivering sufficient Cathode current to the Magnetron over the voltage range of 0 Voltsto approximately 3 Kilovolts is needed to find the Operational Modes of oscillation (there will be several) as the voltage isslowly increased from zero to maximum. Some means of measuring the microwave output power (a microwave thermistor ordiode, or both) is used to identify the power levels attainable in the several modes, and the Cathode Voltage Range for eachmode.

As the Cathode voltage is increased in each mode of oscillation, the microwave power output will increase proportionally untilthe voltage exceeds the maximum for each mode.

Once the mode which delivers the maximum output is identified, and the voltage range of the mode is accurately measured,then a custom power supply can be devised to concentrate efficiently on that desired voltage range. This will enable the outputpower of the magnetron to be continuously adjustable from minimum to maximum within the mode, by simply varying theCathode Voltage.

The output power will be considerably less in Continuous Wave than is produced in Pulsed Drive Operation. It may besufficient, however, to use as a microwave source for your laboratory purposes.

The microwave oven magnetron may be ideal for this purpose since it is designed to operate well over a variable input voltagerange. Making your own Negative Power Supply with sufficent regulation and stability over its range of adjustment is the moredifficult challenge.

More difficult, but by no means beyond your skill levels. Or, in the event that it may be, almost any electronics tech or hamradio operator would be able to provide the needed assistance.

The cost would not be high.

April 9th, 2008, 02:29 AMmegalomania

I actually found the perfect journal article soon after I made my last post. It describes in detail the electronics required tomake a modified domestic microwave oven into a laboratory oven with adjustable power control, and a temperature controlleron/off system. I see now the ideal modified microwave has both a manually adjustable voltage which raises and lowers theoutputted wattage, and a temperature controller that acts as a safety system to turn the microwave off when it gets too hot,and back on when it cools.

Computer controls come into play that are very similar to kiln controllers for ceramics. The ability to program the machine toramp the output of X watts over Y time, hold for a time, then decrease power would be very useful. Ideally the controller wouldset his power output at such a level as to keep the temperature controller from turning off the microwave as little as possible.I gather this could be computer controlled as well, with the computer trying to achieve as little temperature fluctuation aspossible by adjusting the power, and the controller shuts the whole thing off as needed if it gets too hot.

The article is:

Microwave power control strategies on the drying process I. Development and evaluation of new microwave drying system.

W.M. Cheng, G.S.V. Raghavan *, M. Ngadi, N. Wang

Journal of Food Engineering 76 (2006) 188–194

AbstractA phase-controlled electrical power regulator was developed and connected in series with the original cycle-controlled powerregulator of an existing domestic microwave oven. The microwave oven was further modified such that combined microwaveand convectional drying can be accommodated. The system performance was evaluated which included calibration of themaximum microwave output power, determination of the microwave distribution in the cavity, establishment of the relations


between the output power and the input voltage for the phase-controlled power regulator. It was observed that phase-controlled power regulator could be successfully used for quasi-continuous (fast-switching) power regulation with themaximization of power efficiency. The degradation of output microwave power was recorded and the non-uniform distribution ofmicrowave field in the cavity was also verified.

I have a few other good journals articles I found, but none as informative as this one. I wonder if any of the electronics guruswill shed some light on the plausibility of what this article has to say? This article goes above and beyond with its descriptionsof how to gauge the power level.

I read in one of my articles something about a magnetron acting like an induction coil if it is run continually, thus the reasonthey get switched off is to dissipate the buildup of current and send it in another direction thus preventing undue heating ofthe device. I gather the modifications detailed in this article causes the magnetron to rapidly switch on and off and 60Hz? Am Icorrect in my understanding of how this works or not? I should say this type of on off activity is acceptable, probablyunavoidable if indeed the magnetron heats up if not shut off; it is the 10-15 seconds of being off part that is undesirable.

April 9th, 2008, 06:36 PMPositron

Mega and All,

The "phase-controlled electrical power regulator" is nothing more than a light dimmer. The light dimmer in the article ischopping up the incoming 120V power to the high-voltage transformer in the microwave. Each pulse (of varying width...andtherefore of varying power...) occurs every 8.3 milliseconds...plenty fast enough for good temperature regulation.

So, as simple a concept as this is, there are still a few caveats.

1. A magnetron requires two things to generate microwave power. One is filament power, which is a low-voltage (around 10V)The other is is high voltage power.

Read in the article that the diac/triac circuit (light dimmer) is cutting the high voltage power on and off to regulatetemperature, while the filament stays continuously connected to the power source.

So, you must have separate transformers. One for filament power, and one for high-voltage power. For the high-voltage poweryou can just use the transformer that comes with the microwave. For filament power, you must source a transformer (of thecorrect voltage and current rating) for the filament in the particular magnetron that you're using.

p. 191: "For keeping the filament functioning a new filament transformer which had its own power source was introduced toreplace the original one."

Also, when a light dimmer (basically a high-speed switch) is switching a transformer, there will be huge voltage spikes formedwhen the light-dimmer "switch" lets-go of the winding. This spike must be suppressed with a snubber circuit...which ismentioned in the article.

Short answer, yes it will work if those two things are taken into consideration.

April 12th, 2008, 05:30 PMProdigyChild

I have my doubts about this simple design. The original circuit contains a voltage doubler - a diode + a capacitor.Applying a dimmer circuit to a (transformer plus) capacitive load is kind of a short-circuit :eek:. If their setup survived then itwas only luck.

It is possible to oversize the Triac but you can't oversize the HV rectifier diode because you want to reuse it. The diode willeventually die from repetitive overcurrent spikes.

Yet another example of published scientific bullshit. Perhaps the other people cited in the paper who did not come up with thehigh-frequency switching idea were all smart enough to figure out its incompatibility to the voltage doubler circuit :p

April 21st, 2008, 03:08 AMPositron

The rectifier is already seeing high-current pulses during normal use.

The rectifiers are rated for the surges of current that it takes to bring the capacitor back up to voltage, after the load hasdrained the charge during the low-line condition. You are correct that yes, there will be high-current pulses, but I believe you'reincorrect in that it's such a big deal.

The current ratings (both average and pulsed) of rectifiers are based on the maximum allowable die temperature. Mostrectifiers can handle HUGE pulsed currents as long as they don't get too hot. Which, in the situation with the light dimmer +voltage multiplier circuit, I don't believe it will. It's a current-over-time thing.

Rectifiers are tough to kill anway. I have personally melted the solder off of the leads of microwave oven diodes....and had touse gator-clips (a mechanical connection) to hold them onto the wires so that I could continue to use them! (I have piles ofthem, they're sacrificial).

You were a bit quick to bash the article, in my opinion. Unless you are REALLY good, I recommend refraining from doing suchthings until you've tried it yourself ;)

Pretty good almost-catch though...

April 21st, 2008, 11:21 AMmegalomania

I found a microwave yesterday referenced in another journal article as being one of the only models with a continuouslyvariable output rather than a pulsed on/off output. The Panasonic NN-T551 has four power settings with the max being 900W.I couldn't find any on sale, and I am not so sure this is the only microwave oven to have this feature. If Panasonic made one,they may have made additional models by now.

Perhaps a maintenance guide or schematic of this model could shed some light on methods to get a variable power output. I


have seen websites that offer maintenance guides, but not for free.

This Panasonic model uses four buttons to achieve lower power settings, so they must be avoiding a variac for some reason.Probably cost.

As for the article, they did actually build the system, as has at least one other researcher. It must work, but researchers onlypublish good news, they rarely publish things that don't work, or that fail. They will, however, publish about other peoplesideas that do fail when they tried it for themselves.

In another modification to increase the applied power of microwave energy for plasma generation...

"Microwave-induced plasma reactor based on a domestic microwave ovenfor bulk solid state chemistry" by David J. Brooks and Richard E. Douthwaite; Review of Scientific Instruments, 75, 12, 2004, pg5277-5279

... the researchers applied a brass box to the inside of the microwave oven attached to the waveguide to decrease the volumeof the cavity, and thus increase the applied power of microwave energy to their samples.

I can't attach this file because it is watermarked with the downloaders access information. Basically, it looks like the scientistsattached a section of waveguide that fits inside the oven chamber, with a water reservoir at the end to soak up excessmicrowaves. The water reservoir has cold water continuously circulating through it. They report an increase of 114K to 174K withthis modification using inorganic salts with known melting points as their temperature gauge. They reported a maximumplasma temperature of 1400K at 900W with gasses other than argon.

That figure does not seem right for a plasma temperature, it is too low by half to a third I would think. I think what they meanis they were able to heat a capillary tube to a temperature of 1400K with a plasma.

Still this is rather discouraging if that is the plasma temperature. To produce NOx gas from air would require plasmatemperatures near 5000K. The plasma temperature may be a function of applied wattage, and 900W is not powerful enough. Ireviewed a few other references I have for microwave plasma systems and they all seem to have a power output of 2kW ormore.

April 27th, 2008, 08:28 PMProdigyChild

Just because one experiment is in accordance with a theory does not mean the theory is correct.

Another: If you want to drill one hole through 5cm of concrete you can use wood drills - especially if you have multiple ofthem. Most people won't do that.

No, this author proposes an idea each absolutely uneducated person (in terms of electrical engeneering) would come up with.That's fine as long as he does publish such on his private web-site. It is problematic if such an idea get's a scientifc touch(more serious).That's why I was quite angry about the article and the author and still I am. And one question remains: why has nomanufacturer come up with that simple design so far?

Poor designs don't necessarily show their flaws immediately. Failing capacitors on motherboards, exploding batteries innotebooks are extreme examples. Both were not discovered in the beginning. Semiconductors DO degrade. There is no sharpline between operational and broken. How long will the cheap Chinese torch light work properly, that permanently overheatsthe LED? Long enough to sell that cr*p for sure. But you'll never get the umpteen thousands of hours of life time.

I found on the net some information about microwave ovens and for the first time I read that a MOT has a 'magnetic shunt'built in to prevent short-circuit. I thought only NSTs and OBITs have this. That's why the author was lucky.

Consider me an a**hole but I can't judge 'torturing electronic devices' as good.

April 29th, 2008, 02:39 AMmegalomania

Would you care to explain a little more about what you think the author is doing wrong? I can't exactly see what the problem isas I am not too familiar with the nuances of electronics.

The original circuit contains a voltage doubler - a diode + a capacitor.

What do you think a correct solution would be for this setup? How would you protect the diode so it will not fail from currentspikes?

I have been reading more about the Arduino board and its various projects (http://www.arduino.cc/). It seems quite likely thatsome very inexpensive sensors could be incorporated into DIY scientific instruments to be controlled by a computer.

One of the fancy features of the $10,000 CEM microwave benchtop reactor is a computer programmable scheme to customizepower levels and reaction times. This is rather like how kiln controllers ramp and soak pottery. It requires a very sophisticated,and very expensive, temperature controller to handle more than two temp and time presets. With a computer interface therewould be no limit to what you could accomplish.

There is an Arduino project to measure VOCs (volatile organic compounds) using a VOC sensor available from FigaroEngineering Inc. (see http://www.instructables.com/id/How-To-Smell-Pollutants/). I noticed they have an ammonia sensor too.Although I didn't see any prices, I gather these sensors are extremely inexpensive.

I could possibly incorporate the ammonia sensor into my ammonia burner for the production of nitric acid. I am alreadybuilding a temperature controlled electric furnace for it, and the addition of the Arduino could make it more sophisticated.Quite possibly the ammonia sensor could be used to determine the concentration of ammonia vapor from an ammoniagenerator. I want to use the U2A (urea to ammonia) process to generate ammonia, but the quantity of ammonia producedwould vary wildly depending on a number of variables including temperature, pressure, and concentration of urea solution.With this sensor I could have the computer maintain a steady ammonia output by keeping the reaction at an optimaltemperature, and it could tell me when it is time to add more urea solution because ammonia concentration would drop.

This sensor could also detect the presence of unreacted ammonia after it passes the catalyst. One of the engineeringchallenges for this apparatus is finding the optimal residence time of ammonia on the catalyst, to fast and you get unreactedammonia, too slow and you get nitrogen and hydrogen... Using the Arduino, I could start with a very fast ammonia flow,


http://www.instructables.com/id/How-To-Smell-Pollutants/).

detected by the sensor, and slowly decrease the velocity. When ammonia can no longer be detected, that's the optimalresidence time.

I looked a little for a NOx sensor, but I did not find one (the gasoline exhaust sensor from Figaro detects CO, CO2, and H2).This would be the ideal gas to measure.

April 30th, 2008, 07:55 AMBlackFalcoN

I found this link while researching this topic a bit more in-depth:

http://www.geocities.com/vsurducan/electro/micro/micro.htmorhttp://rapidshare.de/files/39271986/MICROCONTROLLER_BASED_INTERFACE_UNIT_FOR_5KW_MICRO WAVE_OVEN.pdf.html

It's the design & construction for a continues wave, microcontrolled 5kW Microwave oven with variable temperature control andsensors.

It utilizes the PWM technique I described before. (Which I still think is the approach to take for this project)

It's design and functioning seem pretty solid to me.What do you all think about the design and do you see any shortcomings ?( just because it works does not mean I can't be improved for our purposes ;) )

The firmware part is a bit complex to understand at first because they utilize a MicroChip PIC16F877, which is a bit harder toprogram and flash for the amateur electronic engineer, but as I said before, that could easily be replaced by a Arduino MCU.

April 30th, 2008, 11:01 AMBlackFalcoN

This patent is also relevant to the topic:

http://www.patentstorm.us/patents/5354972-description.html

Field of the Invention:

The present invention relates to a power supply for a microwave range utilizing a pulse width modulation signal, andparticularly to a power supply for freely varying the output voltage.

EDIT:

http://www.agrenv.mcgill.ca/agreng/theses/theses/313ZhenfengLi2004/313ZhenfengLi.pdf

'Design of a Microcontroller-based, Power ControlSystem for Microwave Drying';

Microwave drying is an energy-efficient drying method.

The output power of most commercial microwave ovens is controlled in an intermittent fashion, where the amount of microwaveenergy is determined by the ratio of “ON cycles” to “OFF cycles.”

To provide a more efficient and continuous power control for the magnetron, a microcontroller-based, feedback power controlsystem was developed.

...

An alternate method of power control is pulse width modulation (PWM). It can offer better output power spectral characteristicsthan phase control and is increasingly being adopted in modern electronic power converters (Trzynadlowski, 1998).

May 2nd, 2008, 09:16 PMETCS (Ret)

Here's an approach to varying the Cathode Supply to the Magnetron that is rather simple:

May 6th, 2008, 07:03 PMProdigyChild

What do you think a correct solution would be for this setup? How would you protect the diode so it will not fail from currentspikes?

I would put an inductor in series with the MOT transformer secondary side, to limit the current slope. Perhaps a resistor parallelto the inductor to reduce the ringing/oscillations. I should do some measurements to determine preferable values.

I looked a little for a NOx sensor, but I did not find one (the gasoline exhaust sensor from Figaro detects CO, CO2, and H2).This would be the ideal gas to measure.

There are those electronic signs in the public that remind us of the air pollution. They show O3, dust, SO3 and NOx so thereMUST be a sensor for NOx!Please note I don't advertise these signs as a source of NOx sensors ;)

EDIT: Just found one at digikey:http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=AD81-NDSee datasheet pdf for details.


http://www.geocities.com/vsurducan/electro/micro/micro.htm

http://rapidshare.de/files/39271986/MICROCONTROLLER_BASED_INTERFACE_UNIT_FOR_5KW_MICRO

http://www.patentstorm.us/patents/5354972-description.html

http://www.agrenv.mcgill.ca/agreng/theses/theses/313ZhenfengLi2004/313ZhenfengLi.pdf

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=AD81-ND

May 7th, 2008, 02:08 PMFUTI

Guys I have a question in-line I think with topic but out of current line of speech within this topic. You guys talk about MWreactors and detectors etc. I just don't know where to find filter that cut-off visible light, since I'm making a homemade UV-lamp. All other parts are easy to find and I got them. What are they made from? Where to find them? Is there somehomemade version I'm not aware? Thanks. Mods please move this question if you find it misplaced.

May 8th, 2008, 05:08 PMmegalomania

I searched for these "high pass" filters for transmitting UV light and excluding other wavelengths not that long ago. Such filtersare sold by Edmund Optics (www.edmundoptics.com). Beware that they are extremely expensive! Even the factory seconds arequite pricey.

I too have been looking into building a UV light source for photochemical reactions. I keep getting stuck on the prices ofindividual components. It seems to be cheaper to get an aquarium UV sterilizer as a kit rather than get each componentseparately.

There is a project at the Renewable and Appropriate Energy Laboratory (RAEL) at University of California at Berkeley that isbuilding inexpensive UV sterilizers for third world countries (http://rael.berkeley.edu/old-site/uvtube/uvtubeproject.htm).

For the life of me I can't figure out if a regular ballast for fluorescent lights will work fine on a germicidal UV bulb. I can't seemto find any inexpensive lights with a high enough wattage to run a high powered bulb.

One of the great ironies of the fluorescent tube industry is that the UV bulbs are the same as regular bulbs, except they haveno phosphor coating, and the UV bulbs cost 20 times as much. How can something with less material cost so much more?Granted it must be because of the quartz glass used in UV bulbs allowing maximum UV transmission, but only IF themanufacturer uses quartz glass...

Now that I am learning about microwave induction lighting, it seems microwave and UV photochemistry are a perfect match :)With electrodeless UV bulbs, you can zap them in a microwave field and they will emit UV light indefinitely. I have not foundany concrete sources that give prices of these bulbs yet. Induction lighting is still a somewhat new concept for the consumerend of things, and lab or industrial equipment is still prohibitively expensive.

I have considered making my own bulb. The idea is not that terribly far fetched either. With some rudimentary glass blowingof a quartz tube you fill the bulb with 5 mg or mercury and argon gas. You can even get the gas + mercury from fluorescentbulbs. I have worked some with vacuum and gas systems in the lab, so I know the rudiments of the setup. There is a verynice setup on the MAKE blog about a guy who built a neon sign DIY system superior to commercial systems. He built itbecause some professionals in the field told him it was impossible to build your own... I love stories like that.

May 8th, 2008, 05:43 PMProdigyChild

FUTI, instead of searching for a filter that absorbs all visible light you can use a dichroic mirror that reflects only the UV-lightyou need.

Dichroic filters are not that expensive, see:http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=1734

EDIT: Hahaha. Mega has overtaken me!

May 8th, 2008, 06:24 PMFUTI

Guys I envy you sometimes for the fact that you live in the land of plenty, which isn't my story. For example today I asked acompany that sell bacterial strains how much would cost to obtain harmless test strain so that students can learn the trade onit. In USA it cost less then 80$(+transport), for me here price is 460$...let's talk about building prices.

I tried also to buy spare filter for UV lamp from the guys that sold my lab a new UV lamp. They didn't even respond to thefu*king e-mail! That is one firm I won't buy anything from ever. I have one half-usable filter from old UV-lamp (which had twoof them but they are degraded badly do to I presume thermal stress) that I will use somehow I guess. I was looking aboutfilters for UV light and found about Wood's glass and also this page (http://msp.rmit.edu.au/Article_04/06.html) . Do youthink I should try to make that or just stick to what I got now?

And I'm glad that Mega and I share some common interest in chemistry...I will also try to make photo-reactor from the rest ofthe parts available I have.

May 9th, 2008, 08:35 PMETCS (Ret)

Here are a couple of good resources for studying the UV lamp characteristics:

http://members.misty.com/don/uvbulb.html

http://www.negativeiongenerators.com/UV-C_spectrum.html

They both have additional links for in-depth study.

August 6th, 2008, 09:25 PMfractional distiller

With Regards to a microprocessor that can be used for monitoring and or possibly used for a control in a synthesis processone item of interest would be the microprocessors available to the public through http://www.parallax.com/.

I first encountered the parallax products in my younger years while attending a camp for robotics. The kind where the parentspay outrageous amounts of money for their children to play with electronic components, while college students tell them thatthey are so smart.

Besides being told that I was a unique and special individual with great creativity as I followed my predesigned diagram with afew variables for "student creativity". I did actually come to realize that the the projects that we were building were completelyuseless but the technology and tools that could be incorporated with it was not.


http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=1734

http://members.misty.com/don/uvbulb.html

http://www.negativeiongenerators.com/UV-C_spectrum.html

http://www.parallax.com/.

The controller I am familiar with is of the basic stamp variety. They offer packages that can be used and maybe very useful forprocess control. They offer thermocouples and flow meters and may other useful probes that can be used for process control.

August 7th, 2008, 01:18 PMmegalomania

Wow, fractional distiller, that is very cynical, nevertheless absolutely true.

It takes a little digging to get to their prices, and I see you can request a catalog.

August 25th, 2008, 02:23 PMPositron

Sorry to post this so late. It's been awhile since I surfed through this section.

UV filters are readily obtained in the form of glass envelopes that shield High Intensity Discharge (HID) lights.

There are two bulbs in these HID lights; one is the small, active, light-emitting gas-containing bulb with electrodes inside. Theother, is an oversized (to lower the energy density and temperature, I'm sure!) giant envelope that surrounds the smaller bulbin the middle. It's this larger glass envelope that you're after.

I once severely damaged my corneas by using a mercury-vapor HID light that had a busted UV shield. It took about 15minutes of working near this light to put me out of commission. Trust me, this shield is the real deal.

I'd advise trying to look up the transmittance curves of this glass, so you know exactly what wavelengths it will or will not pass.Keywords will be wavelength, transmittance, UVA, UVB, absorption, HID, mercury vapor, sodium, metal halide.

August 30th, 2008, 08:28 PMmegalomania

That's the WRONG kind of UV filter, Positron. We want a filter the excludes everything EXCEPT the UV light. The UV light is whatperforms the chemical reaction, but there are too many materials that block it, thus limiting the effectiveness of the reactor. Afilter that passes UV while excluding other wavelengths is not so easy to find (on the cheap).

September 1st, 2008, 08:55 PMtapira1

Did not read carefully the whole tread; perhaps somebody already posted this info before. Here is the way we get UV light forchemical reactions: There are widely available mercury street lamps; they need a transformer to light up. All you have to do isto carefully remove ("destroy") the outher glass envelope which has the phosphor (this turns UV into visible light). Theremainder of the lamp, once turned the power on, emits UV light (watch out!!! exposure to UV may damage your corneas andeven leave you blind. Use protective glasses. Do not expose bare skin to this radiation either; you may get burned.

September 2nd, 2008, 07:53 PMmegalomania

I obtained one of those type of bulbs last year. My problem now is how to power it. I have looked high and low for aneconomic method of producing UV light for photochemical reactions. Without having to pony up for a real UV reactor, thecheapest I have found so far are aquarium UV sterilizers and a DIY electrodeless microwave UV lamp.

There are some specialty LED UV bulbs that have a low enough wavelength, but they have very little power output. I don'tmean the kind of LED lights for UV curing and ROM erasing, the wavelength of that UV light is not short enough.

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