The Black Wire Disease - What's the Cause?

The black wire syndrome is an occupance in battery packs (Ni-Cds) where the negative wire becomes corroded (turns from shinny copper to blue-black). This is the result of either a shorted cell in the pack, the normal wearout failure mode of Ni-Cds, or cell reversal when a pack is left under load for an extended period. The sealing mechanism of a Ni-Cd cell depends to some degree on maintaining a potential across the seal interface. Once this potential goes to zero the cell undergoes what is called creep leakage. With other cells in a pack at some potential above zero the leakage (electrolyte) is "driven" along the negative lead. It can travel for some distance making the wire impossible to solder and at the same time greatly reducing its ability to carry current and even worse, makes the wire somewhat brittle. A switch left on in a plane or transmitter for several months can cause this creepage to go all the way to the switch itself, destroying the battery lead as well as the switch harness. There is no cure. The effected lead, connector, switch harness must be replaced.

This leakage creep takes time so periodic inspection of the packs, making sure that there are no shorted cells insures against the problem. The cells should also be inspected for any evidence of white powder (electrolyte mixed with carbondioxide in the air to form potassium carbonate). In humid conditions this can revert back to mobile electrolyte free to creep along the negative lead. Some "salting" as this white powder is referred to, does not necessarily mean that the cell has leaked. There may have been some slight amount of residual electrolyte left on the cell during the manufacturing process. This can be removed with simple household vinegar and then washed with water after which it is dried by applying a little warmth from your heat gun..

C. Scholefield 8/29/96 return to welcome page

Fast Charging - Will it harm my packs?

Applicable to Ni-Cd and Ni-Mh batteriesFirst, let's define "fast charge". The industry standard is any charge rate that will charge the cells in 1 hour or less.

This fast charge capability thing is very interesting. Almost all ni-cds manufactured today for R/C systems can accept fast charge (up to C rate, that's the rate at which you can charge the cells in approximately one hour). Cells that are specifically sold as fast chargeable go through another step in the process. This step involves charging a sample from the production lot and then measuring the end of charge voltage. Cells with the highest end of charge voltage are then analyzed for internal pressure. If the internal pressure is acceptable, that is not above a preset limit, the whole production lot is "blessed" as being fast chargeable. Of course this adds a finite amount of cost to the cell as they must be "formed" prior to being ship in order to be fast chargeable.

Cells not destined for fast charge applications are shipped "unformed" by some manufacturers. Forming the cell is the process of the first charge after it is assembled. Nothing more, nothing less. When you charge your R/C system packs for the first time you are "forming" them. This is why you see the instructions telling you to charge the packs for 16 to 24 hours before you first use the system. Some manufacturers ship all their cells in the formed condition as part of their manufacturing process.

So in most instances you are safe fast charging the R/C packs (transmitter or receiver) on the market if you first make sure they get a good first cycle formation charge - 24 hours at the slow rate. Where the problems arise is that some of the fast charge systems available are a little sloppy when it comes to terminating the fast charge, or they are pushing the cells too hard (higher than the C rate charge) and then damage occurs. As a rule of thumb if you packs are not getting hot (slightly warm is OK) you are not damaging them in the fast charge process. When pushing too much current into cells not designed to accept it there is the risk of driving the cells above 1.6 volts (the hydrogen over voltage point) and electrolyzing the water in the electrolyte and generating hydrogen. This is a cumulative event and repeated fast charge at these rates will result in sufficient accumulation of hydrogen to cause the cells to vent. When they do vent there is a chance that the chemical balance will be disturbed and the cell capacity will fade. Understand that the pack may not be fully charged when the fast charge terminates. It is a good practice, if you are going to fast charge frequently, to top off the packs using the slow charger. This will bring all cells to the same state of charge and "balance" the pack. Otherwise the cell that is not fully charged will be the limiting cell on the next discharge. This continues until there is a major unbalance in the pack and one cell can be driven into reverse (if you don't crash first).

cls 2/97 rev 1-07return to welcome page;

Care and Feeding of your Sealed Lead Acid Battery (aka - gel cells)

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Lead Acid (Gel Cell) charging

Lead acid (gel cells) should be charged with a constant potential charger specifically designed for these batteries. These are sometimes referred to as a CVC charger. You can charge them with a constant current charger but you must terminate charge when the voltage reaches 14.7 volts. You should not exceed the C/10 charge rate. If you have a 7 Ah battery in your field box the maximum constant current charge rate should not exceed 700 mA. It will take about 14 hours to charge from a fully discharged state (voltage less than 12 volts).

A CVC (Constant Voltage Charger) is exactly what the name implies. It is clamped at a certain voltage and puts out all the current it can until the battery reaches the clamp voltage, usually

something around 14.5 volts, then the current drops off to maintain it at this voltage. A constant voltage charger is characterized as one having a current capability of supplying a fixed voltage to whatever load is applied. A constant current charge on the other hand will provide whatever voltage is necessary to force a fixed value of current though a load. Constant current charges have a much higher internal resistance than the load so that any variation on the load will not change the current being supplied. Constant voltage charges have a very low resistance as compared to the load and will supply whatever current necessary to maintain a given voltage at the load.

Many inexpensive chargers used for sealed lead batteries are what is called taper chargers, these are set up so the voltage tapers off as the full charge voltage is reached. True constant potential (CVC) chargers can be quite expensive so a compromise is made in the design to control costs.

We have used the term sealed lead battery in this discussion. These batteries are not truly sealed as cylindrical Ni-Cds are. They have a gelled electrolyte system where there is a modest recombination of the oxygen in overcharge in some designs. All require venting of the oxygen and hydrogen byproducts of charging and discharging. This is why you should never totally seal these in a field box where these gasses can accumulate. Mixtures of oxygen and hydrogen can cause spectacular "events" if a spark is provided (from an electric fuel pump motor).  

How much charge is there in the battery? Unlike Ni-Cds you can read the remaining capacity quite easily with a voltmeter.

After the battery has been on rest for a few hours read the voltage (no load). 12.0 volts is essentially fully discharged while 13.0 is fully charged. This is a fairly linear relationship so a reading of 12.4 volts means you have 40% of the capacity remaining.

Never leave a lead acid battery in the discharged condition. The lead acid battery should never be left to set in the discharged condition or sulfation will result. The sulfuric acid in the electrolyte reacts with the sponge lead active material and forms lead sulfate. It is a poor conductor. This coupled with the H2O left after you take all the S out of H2SO4 is also a poor conductor so trying to charge requires a lot of voltage to push the current through required to convert the active material back to the charged state. Sometimes they just cannot be brought back from the sulfated state.

The good news is that sealed lead batteries retain their charge much longer than Ni-Cd, At room temperature it's well over a year. So all you have to do is make an occasional open circuit voltage check to see if you need to charge it.

For a great deal of information on Flooded Lead Acid (Automotive and Deep Cycle) go to:

 Automotive & Deep Discharge Information

This material is oversimplified I know, but more detailed explanations can be had at my commercial rate of $125/hr plus expenses.

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Ni-Cd Life - or why is down so quick?C. Scholefield

While volumes have been written on this subject I would like to relate it to the specific application of R/C , separating fact from fiction and enabling the R/C fraternity to focus on more serious issues of the day, like convincing your wife it's too foggy to clean the pool so you're going flying while the field is not so crowded.

The primary failure mode of Ni-Cd cells (outside of user abuse) is separator deterioration. This will occur in all Ni-Cd batteries as they age. The separator breaks down allowing the plates (electrodes) to touch and short out the battery. Millions of testing hours on thousands of cells has established the mean time to failure of a single cell to be 8 years for cells/batteries maintained at 25C (77F). Higher temperatures will significantly reduce these numbers. Mean time to failure means the time that it takes for half the cells in a given population to fail. As the cells are built into packs the mean time to failure decreases. For a 4 cell receiver pack the mean time to failure comes out to be 5.7 years while an 8 cell transmitter pack falls to 4.8 years. Now it is completely possible that the average R/C modeler doesn't want to tempt statistics to the point where half of his battery packs should have failed. A more reasonable number would be the expected time for 0.1% of his batteries to fail. The number comes out to 58 weeks for a receiver pack and 49 weeks for a transmitter pack. For the more adventurous willing to live with 1 failure in a hundred, he can stretch his receiver pack to 103 weeks and his transmitter to 87 weeks. Does this mean that he should rush out and buy new packs at these intervals? Not really. Proper battery monitoring, while it may not significantly increase life, will give you ample warning that your pack should be considered for replacement. Remember, normal failure is the deterioration of the separator system. As the separator deteriorates (oxidizes) self discharge rate of the battery increases significantly. A pack that looses 15% or more capacity over a week of open circuit stand is at risk. A pack that looses 10% overnight should be used for ballast only. Check your pack with a cycler or some technique that gives you the amount of capacity available immediately after charge and then (after fully charging again) after a rest period of 5 to 7 days.(NO, this isn't MEMORY!). Doing this at least quarterly (if you are fortunate enough to live where you have a flying season longer than 3 months) will greatly increase your odds of crashing by some other defect than battery failure.

The number of cycles you put on your battery is secondary in the life equation, again, assuming you don't abuse them by high rate over charge, vibration or exposure to high temperature. I know of very few people that totally exhaust their battery packs while flying (at least not as a matter of course) so the packs seldom see a full discharge and the risk of cell reversal is nil. Test have demonstrated that hundreds of cycles of reversal where 140% of the rated capacity is taken out in a driven discharge resulted in a capacity loss that was barely measurable. Many multi speed power tools use the technique of tapping the battery for speed control with no adverse effects on the battery. A single cell can be discharged through a load to zero volts without damage. In fact this is a good way to determine if a cell has suffered from separator deterioration. A cell discharged to zero volts will recover to over 1 volt open circuit if left to stand. Those that will not are

approaching the steep part of the failure curve and could be a crash waiting to happen. Bottom line: the number of full charge/discharge cycles that can be accumulated by today's Ni-Cd technology is in the 400 to 500 cycle range. Of course partial discharges seen in the R/C application can extend the use cycles to significantly more than this. It doesn't take a battery expert to figure out the amount of flying time you can accumulate on 500 full discharges. We are talking in excess of 1000 hours. If you put in a full two hours a week in the air every week year round, you would be well into the next century before you reached 500 cycles. Separator failure or old age will probably do you in before you run up 500 cycles. Meticulously recording the number of discharge cycles to establish a replacement schedule can be a study in futility and should be left to the electric R/C indoor microfilm pylon set. Don't worry about reversal. If you have left your switch on overnight or for even a couple of days, just give the pack a good long slow charge using your regular charger supplied with the system for 48 hours and you will probably be OK. It would be prudent to run a capacity check cycle after such an incident just to make sure.

Long term overcharge, leaving your packs plugged in to the charger supplied with the system, while considered an acceptable practice for many consumer applications can contribute to a reduction in battery life. First, as a battery goes into overcharge, oxygen is generated on the positive electrode and then recombined on the negative electrode. This oxygen rich atmosphere only accelerates the oxidation of the separator. As the oxygen is recombined on the negative it generates heat.We all know how to make a chemical reaction speed up, turn up the heat.

One further phenomena recently brought to light after years of testing is that of cadmium migration. This is a transfer of cadmium metal through the porous separator structure to form a conductive bridge between the electrodes. In simple terms a high resistance short which causes the cell to self discharge, shunts charging current to where the cell takes longer to charge and ultimately, if left of continue, become a hard short which, if happens during a period when batteries are part of, or contributing to the direction of an airborne operation, result in a rapid depletion of model resources. The same testing reference also confirms that the same amount of charge put into the battery in a short period significantly reduces the cadmium migration. Therefore using a simple appliance timer to switch your charger on for about an hour a day minimizes the overcharge and yet maintains the packs at peak charge should an airborne operation be called for at any time. For the experimenter, a charger designed to charge the battery at C rate (1 hour rate) run at a 10 to one duty cycle (on 0.1 second, off 1 second) is more effective than charging continuously at the C/10 (10 hour rate common to most system chargers) and will enhance battery life. For a maintenance charge a 25 to 1 duty cycle is recommended. This pulse charge is better than even a very low trickle charge for maintaining the battery as cadmium migration is driven by passing current through the separator (charging) over a period of time. The rate of cadmium migration does not seem to increase proportionally to the current density, leaving us with the conclusion that getting the job done (replacing charge loss through inherent self discharge) quickly by a pulse of charge current is better than dragging it out with a long sustained overcharge. While this gives battery a break it will probably give rise to a new generation of exotic (expensive) chargers focusing on the

dreaded cadmium migration phenomena (hereafter referred to as CMP, people only take three letter problems seriously) and leave the dreaded memory effect (DME) alone for awhile. Just remember that you can do the same thing with a $5.00 timer and spend the savings on a subscription to your favorite R/C magazine, RCM.

Storing the battery is no big deal. Living in Florida where there are no cool (damp, dark, moldy) basement work shops, I store my batteries in the refrigerator on off flying season (July 3rd 9:30 AM to July 4th 7:00 AM). Those living in Northern climates don't really have anything to worry about (there must be some advantage) but should remember about the trunks of cars and what happens to batteries you leave them in there when you are visiting us for a winter flying vacation.

Looking at the battery voltage after several months of storage is an excellent way to pick out a weak cell (use straight pins to probe each cell). If a cell voltage after several months drops noticeably below any of the others, beware. You have a potential problem and the pack should be relegated to some benign surface application. While we are on the subject of measuring battery voltage, consider getting one of the little digital voltmeters available through electronic hobby outlets. They give you a precise reading and are well worth the modest investment. Second piece of advice. don't listen to the R/C car guys when it comes to batteries, they have never experienced the thrill of real rip roaring, crank shaft bending, dirt in the transmitter, kind of crash and as a consequence take liberties with batteries that would make Leclanche and Volta turn over in their graves to say nothing about causing me just a little heart burn when they get me cornered in "technical" conversations.

Now that we have addressed the life of the battery pack to some extent we should take a quick look at the life of the plane, which is directly connected to " How long can I fly on a fully charged pack?

Know what your system consumes in the way of energy per minute of flight. This can be determined by first charging a pack and then discharging it on a cycler to determine how much capacity it has - fully charged. Then recharge and go fly. Record your system on time and immediately discharge the pack when you return home. This will tell you how much capacity you have left. Lets say you fly for 40 minutes and when you discharge the pack you get 390 mAh. From your initial discharge from a fully charge pack you got 585 mAh. This would mean that you discharged 195 mAh in the 40 minutes you flew or about 5  mAh/min. From this you would know that your pack is good for 116 minutes of flight time under the actual flight loads. Now we don't  want to take it this close so give yourself (and your plane) some margin of safety -25%. So this would set your SAFE flight time to 75% of 116minutes or 1 hour 27 minutes. This should be done for each plane.  Also it should be done for your transmitter at least once just to accurately characterize its "flight time". The system usage will vary, depending on your flying style, size of the plane and number of servos used. (Excerpt from article on  Keep your batteries in the ready state without damaging overcharge. )  

CLS 1/24/91 (published in RCM 6/91) Rev 10/31/96 Rev  2/24/04For a simple solution to maintaining your packs at the ready state Click here . return to home page

Negative Pulse Charge, or "Burp" Charging

Fact or Fiction?The concept of applying a short discharge pulse during the charge cycle sometimes referred to as "reflex charging" or "burp charging", has been with late 60s with patents by W. Burkett & J. Bigbee [3,597,673" Rapid charging of batteries and W. Burkett & R. Jackson [3,614,583 "Rapid charging of batteries"] and assigned to the McCulloch Corporation.

Burkett, an individual with great drive and somewhat uninhibited by the lack of any test substantive test data, enlisted the help of a Professor at Stanford to come up with a reason why the negative pulse charge technique did what Burkett claimed. This individual, striving for academic elegance, came up with the hypothesis that the negative pulse may have stripped away the gas bubbles on the plates and thereby enhanced the charge efficiency and reduced the temperature and pressure build up. He stated it was like burping a baby. Burkett liked the sound of this and it became his theme in promoting the concept. The fact that he was a prolific writer did not detract him from his quest, as he had his concept published in numerous trade magazines and technical journals hungry for a charging break through in the emerging market of cordless products.

After the patent was awarded he took it to General Electric, then the leading Ni-Cd manufacturer in the US, where it was analyzed in detail. General Electric disappointed Burkett when, after extensive testing, they could find no conclusive evidence that the negative pulse offered any advantage. Burkett then proceeded to find other interested parties that would be less critical, and take his word for the phenomena. He sustained the venture for several years mostly by obtaining government contracts to further study the effect of the negative pulse technique for both sealed and vented Ni-Cd systems.

With the expiration of the patents many saw the opportunity to make a great deal of money from the ignorance of battery users and thus it has proliferated in many variations and forms. General Electric, confronted by battery customers who had bought into the Burkett scheme of charging, tested and retested the concept as each new variation was presented. The results were the same in each instance. It has never been demonstrated to have any advantage over conventional charging, either on charge efficiency, the performance or the life of the battery. While many claims have been attributed to this technique, none have ever been substantiated in the laboratory. Fortunately it does not harm the battery in any way and since the concept makes for a rather elegant marketing

technifact, it has been adopted as a way to promote the sale of charging systems by numerous companies in which marketing dominates technology.

The reflex chargers are for the customer that cannot separate marketing from sound engineering and feels compelled to perpetuate this hoax while providing a healthy income for its proponents. If reflex charging had any merits that would enhance the performance of batteries the battery manufactures would be supporting it with vigor as would the major suppliers of battery powered products. Since is does no harm to the battery, the battery manufacturers are reluctant to focus on the pointlessness of some customers that insist on using it and risk a technical confrontation that would embarrass the proponents and jeopardize sales. CLS 1/97 back to home page ******

Using a Timer Can Improve Battery LifeOne of the failure modes in Ni-Cd cells is shorting. While many things can contribute to shorting one of the significant contributors is cadmium migration through the separator where it forms a conductive bridge, ultimately shorting the cell

Cadmium migration is a function of the time the charge current is flowing through the battery and less a function of the level of current. Therefore we have found that high pulses of charge current to maintain the charge state are better than a steady low rate (trickle) current. This is very difficult to quantify as their are many other factors contributing to the life equation but improvements in battery life of 10 to 20 percent by pulse charging vs trickle are not unrealistic.

Therefore we have found the sustaining a pack at the fully charged state by way of pulsing the charge is better than an continuous trickle charge.

Some charges employ this technique. You can do the essentially the same thing rather simply and at a very low cost.

Simply connect your regular wall module charger that came with your system to an appliance timer. Intermatic makes a good unit for around $5.00. Set the trigger pins on the timer so that it is on for 1 hour a day. When you return from a flying session turn the timer wheel so that the on off triggers come up in 14 to 16 hours. Then turn the timer knob to on. This will give your pack a full charge and then a sustaining charge for 1 hour a day. The battery can be left in this manner for a long time between flights and still be maintained at a fully charged state with minimal overcharge.

If you only fly a couple of flights, you can just set the timer so that you get 6 or 8 hrs before you go into the 1 hr.day mode. If we assume a normal 2 hr flight time for a system and you only fly 20 minutes. Then the charge you need to return is 20/120 times 16 hours, or about 3 hours.

Know what your system consumes in the way of energy per minute of flight. This can be determined by first charging a pack and then discharging it on a cycler to determine how

much capacity it has - fully charged. Then recharge and go fly. Record your system on time and immediately discharge the pack when you return home. This will tell you how much capacity you have left. Lets say you fly for 40 minutes and when you discharge the pack you get 390 mAh. From your initial discharge from a fully charge pack you got 585 mAh. This would mean that you discharged 195 mAh in the 40 minutes you flew or about 5  mAh/min. From this you would know that your pack is good for 116 minutes of flight time under the actual flight loads. Now we don't  want to take it this close so give yourself (and your plane) some margin of safety -25%. So this would set your SAFE flight time to 75% of 116minutes or 1 hour 27 minutes. This should be done for each plane.  Also it should be done for your transmitter at least once just to accurately characterize its "flight time". The system usage will vary, depending on your flying style, size of the plane and number of servos used.

cls 5/22/97 Rev 2/24/04 return to welcome page

Parallel Operation = Reliability & More Flight Time

The use of redundant parallel fight packs (packs may be of different capacity but MUST be of an equal number of cells) is an excellent way to increase the available flight time and significantly improve the reliability of the on power system. The simplest means is to run two complete wiring harness, switches and charge jacks from each pack and plug one into the normal battery port and the other into an extra channel on the receiver. No diodes

or isolation is required (see below). This is simpler and more reliable than some of the complex battery backup systems being offered on the market. Whether you are using 4 or 5 cells is your option, remembering that a 5 cell pack will provide more power to the servos but at the same time discharge faster giving you less flight time.

Parallel charging of Ni-Cds is not recommended due to the tendency of the cells to have the voltage drop off after they reach full charge. Should one pack have a slightly different capacity than the other then it will reach full charge sooner and the voltage will start to drop off allowing more current to flow into this pack. The other pack may not then reach a full state of charge. Repeated charge/discharge cycles under this parallel arrangement causes additional charge unbalance. While you may experiment and find that you get what appears to be both packs charged you will eventually run into problems with this arrangement. As an extreme, take the case of two packs, one having 250 mAh capacity and one having 600. The smaller capacity pack will reach full charge much sooner assuming that there is at least an equal "sharing" of charge current. As it peaks and the voltage declines slightly due to the heating of the battery as the oxygen is recombined it will begin to take more and more current to maintain a voltage equal to the as yet uncharged pack and the voltage tries to drop further and demands even more current to keep it up. This pack will then be taking nearly all the charge current leaving the larger pack woefully short during what would be perceived as a normal charge time like 16 hours.

Many pseudo battery "experts" put forth the argument that plugging two battery packs into the same receiver with out blocking diodes is NOT a good thing, claiming that his creates a host of problems and the two packs will end up fighting each other or "cross charging".

These concerns show a lack in the understanding of the charge and discharge potentials involved in Ni-Cd cells. One pack cannot charge the another (equal number of cells) as the discharge voltage of a pack can never be as high as the voltage required to charge the other pack. For the doubters here is an experiment: completely discharged one pack to 4.0 volts and then connected to a fully charged pack having an equal number of cells. There will be less than a 10% transfer of charge in a 24 hour period. Since shorts rarely occur in fully charged packs the risk of one pack "dumping" into one with a shorted cell are insignificant. A simple ESE preflight test would detect a pack with a shorted cell.

While it is a fact that the typical failure mode of a battery is for a cell to fail shorted there are some subtleties here that escape many people. First,one of the major causes of "battery" failure has nothing to do with the batteries themselves but rather with a switch or connector in the battery circuit. The dual redundancy concept is to protect against the failure having the highest probability - that being the circuit path from the battery to the power buss in the receiver. Adding more components to this path, like regulators and/or diodes isn't going to help the matter but rather adds to the probability of failure.

Perhaps the following discussion on the nature of shorts will better help the modeler understand.

While it is agreed that shorts are the failure mode in Ni-Cds batteries one has to look further into the "when" of the failure.

A short develops in a Ni-Cd when conductive particulate bridge the separator or the separator itself deteriorates to the point where it allows the positive and negative plates to touch. Rarely does the short occur all at once but rather building up a very small conductance path termed "soft shorts". In a charged cell the energy in the cell will blow away any short as it tries to develop. You've heard about "zapping" cells. The cell actually zaps itself before the short can develop. Only in cases of severe overcharge at high rates can the separator melt down to the point where the plates contact each other (hard short). In this case the energy in the cell then dumps and we have what is referred to as a hot steamer, the electrolyte boils, nylon in the separator melts down and is forced by the steam through the vent. On some occasions the vent is clogged by the molten nylon separator and becomes inoperative causing the cell to rapidly disassemble. So under normal circumstances a cell maintained at some state of charge is much less likely to short than a cell that is completely discharged. It should be noted however that the self discharge increases rapidly in cells where there is a short building (high resistance -soft short) due to separator deterioration and/or cadmium migration. One other shorting mechanism is a manufacturing defect where the positive or negative collector tab bridges the opposite plate. These usually fall out before the cells are shipped or assembled into batteries.

Preflight procedure should involve checking each battery separately. First check each with ESV through charge jack. You should get nearly identical readings, then switch one on, check controls, switch off and then switch on the other battery, check controls again, then turn both systems on and fly with confidence.

Summary: Diodes are not required. Packs must be of the same number of cells. Packs may be of different capacities. Individual charge jacks must be provided for each pack (and not interconnected). Total capacity available will be the sum of the individual capacities. Specialized chargers are not required since standard packs (600-800 mAh AA packs)can be charged employing regular system wall chargers (1200 to 1600 mAh should cover most giant size projects).

cls 5/97 return to welcome page  

Shorts, how they occur.A short develops in a Ni-Cd when conductive particulates bridge the separator or the separator itself deteriorates to the point where it allows the positive and negative plates to touch. Rarely does the short occur all at once but rather building up a very small conductance path termed "soft shorts". In a charged cell the energy in the cell will blow away any short as it tries to develop. You've heard about "zapping" cells. The cell

actually zaps itself before the short can develop. Only in cases of severe overcharge at high rates when the cell heats up significantly, can the separator melt down to the point where the plates contact each other (hard short). In this case the energy in the cell then dumps and we have what is referred to as a hot steamer, the electrolyte boils, nylon in the separator melts down and is forced by the steam through the vent. On some occasions the vent is clogged by the molten nylon separator and becomes inoperative causing the cell to rapidly disassemble. So under normal circumstances a cell maintained at some state of charge is much less likely to short than a cell that is completely discharged. It should be noted however that the self discharge increases rapidly in cells where there is a short building (high resistance -soft short) due to separator deterioration and/or cadmium migration. One other shorting mechanism is a manufacturing defect where the positive or negative collector tab bridges the opposite plate. These usually fall out before the cells are shipped or assembled into batteries.

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cls 12/96

Storage of your Ni-Cd/Ni-Mh R/C Packs"How should I store my batteries at the end of the season? What should I do to them when I put them back in operation?"

The batteries should be removed from the transmitter and plane for longer term storage. Here in the south where a lot of us work out of our garage work shops I recommend putting them in the refrigerator (not the freezer) during the off season. While not so important where your workshop rarely gets above 23 degrees C (74 F) the refrigerator is still a good bet. Why? The failure mode of Ni-Cds is separator failure; this is the material that keeps the plates from touching each other. When it fails, the cell shorts. At higher temperatures it oxidizes faster. In fact, the rate doubles for every 10 degrees C increase.

"Should I store my batteries charged or discharged?" It doesn't really matter, they will self discharge in a few months stored at room temperature. If you are going to store them in the refrigerator the charge will remain for a lot longer so I would discharge them first to 1.1 volts/cell and them put them away. Good cells will just set there in the discharged condition (the voltage can vary considerably but is usually above 1 volt). In a battery with damaged "worn out" separator in the cells, the cells are apt to short if left in a discharged condition. This is actually good since it is the first indication of a cell that's going bad and it is best to replace the pack. A battery left on trickle charge will seldom short out since it is in the charged condition and any short that tries to develop will be zapped by the charge in the cell. Partial shorts (those having fairly high resistance) can be developing that can cause the cells to self discharge at a higher rate than normal and possibly leave you short in the middle of a flight after you just measured the cell when it came off charge with your ESV and everything looked OK.

The reason I recommend removing the batteries from the transmitter and plane is to protect against "black wire" disease. Should a cell short while in storage there is a high

probability that there will be some leakage that can lead ultimately to the "black wire" problem.

Now when your batteries are coming out of storage, before charging, check the voltage without a load on the battery. It should read well over 1.0  volt/cell even if it has not been charged all winter. They should be essentially fully discharged, flat as we say in the business. In this condition if the battery is going bad it will probably have shorted and you will read zero volts on that cell. It may be a soft short, one that could be blown away merely by the simple action of slow charging. Don't do it! It is just lying there waiting to bite you. Replace the pack. Cut out the "good" cells if you want and use them in something less critical than your model. If you have access to a cycler running though a couple of charge/discharge cycles is a good idea just to make sure you are getting the capacity you are suppose to. Anything less than 80% of rated is suspect. Once at the field, pre-flight battery checks are in order, particularly at the beginning of the season. Since those that religiously check their flight packs with an expanded scale volt meter seem to crash less (due to battery failure) one must assume that the ritual is smiled upon by the R/C Gods.

cls 12/96 rev 1/07return to welcome page

HOPE YOU GET CHARGED UP OVER THIS

Red Scholefield  

You were cleaning up your shop and somebody stepped on you charger and broke the plug off.Your significant other wants to toss all those useless charger transformers you saved that were left over from by gone days of cordlessegg beaters, carving knives, mixers, shavers things you can’t even remember. You still have as a remembrance the charger from the dustbuster you kids use when they tried to suck a mud puddle dry.  

On the other hand you are still trying to figure out how to charge the 850 mAh pack you made up from the guts of a new video pack that you salvaged after Uncle George backed over it with his '68 Caddy at your cousin’s wedding. Somewhere in your shop you just cleaned up, you can't find the charger to your glow plug driver and it's very dead as you found out as you tried to sneak in an flight before work at the field and you were the only one there.  

GOOD NEWS!! (and there is no bad news so take heart) You are surrounded by charging opportunities. If we ignore the banal warnings on your collection of orphan chargers warnings like USE ONLY ON HINKENDORF MODEL XL199-06 OR SEVERE DAMAGE COULD RESULT. These warnings are in the same category as USE ONLY GM APPROVED PARTS or FOR INDOOR USE ONLY. When was the last time your

charged your transmitter in the rain?. Notice that all of these little charges have a UL approval mark. It means that these chargers when short-circuited will not do nasty things like catch on fire or electrocute the owner. They may blow an internal thermal fuse, but they will not cause a hazardous condition.  

I have, at no small expense of time (at least 30 minutes), taken on the task of characterizing the chargers lying in and around my workshop to see how they would work in other applications. The term “characterizing" is the term used when you are getting a ridiculous compensation for doing something rather simple. In fact as a reward for reading through this I will tell you how you can characterize your very own charger(s).  

In addition to several Futaba R/C system chargers, I had at my disposal a Black & Decker Dustbuster charger, a Sears cordless screwdriver, A Black & Decker charger of unknown vintage and application an R/C car pack charger for 6 cell packs. Since those of you reading this, must by definition, have a least 1 charger that came with your R/C system and it's a good chance that it is a Futaba charger, let's look at one of them first. Figure 1 shows how the receiver and transmitter portions of this charger work with different numbers of Ni-Cd cells.

 

The chargers were tested to determine at what rate they would charge a range of 1 to 10 Ni-Cd cells. (The capacity of the cell didn't matter since the charge voltage curves are essentially the same as well as the end of charge voltage.) Note from the curve in Figure

1 that for 4 cells the charge current for the receiver portion of the charger is about 50 Ma right where it should be. Likewise for 8 cells in the transmitter section it is charging at the rate it was intended to approximately 50 Ma. But you have acquired a 4.8 volt 1000 mAh flight pack from somewhere and you would like to charge it in something less than a couple of days.

Just make up an adapter to fit the plug on the transmitter side of the charger (Radio shack has matching plugs) and plug into the 1000 mAh pack. From the curve you can see that the charge rate will be 90 mA and much better suited for the higher capacity battery. This should not harm the charger as the power is at the same level. Note that the receiver side of the charger will nicely handle charging your 1 cell glow plug driver at 100 mA. For a 10 cell battery (nominally 12 volts) the transmitter side of the charger would do a reasonable job of recharging you 12 volt lead acid field box battery although it would take about 5 days to fully charge a discharged 5 AH battery. You can tell you are fully charged when the voltage reaches 14.7 volts. If you don't have a digital voltmeter and plan on doing any experimenting you are working blind! They are available from Radio Shack for under $40.They are far better and much more versatile than any expanded scale meter.(See article on Loaded Digital Voltmeter – Better than ESV)

What about those other old chargers lying around. Can they enhance your R/C life style? Figure 2 illustrates their performance on various cell packs.

The chargers depicted in Figure 2 are identified as follows: BD3 -Black & Decker Dustbuster charger rated at 4.4V @ 125 mA carrying the number 133353 00.  

BD4 - Black & Decker charger from unknown application rated at 5.8V DC 1125 mA and carrying the

number 86755.  

SEARS - Sears screwdriver P/N 350930 rated at 5V 0.35 A.  

MILL6 -Millennium charger Model No. CH72RC rated at 8.7V 2W and designed for charging an R/C car 6 cell 1400 mAh pack.  

What useful charging jewels can we draw from this information? Both the Black & Decker and Searschargers would do a reasonable job charging some of the higher capacity 4 cell flight packs.Sears would be better at 125 mA. They would also work fairly well on each others products. If you are turned on to using 5 cell Ni-Cd flight packs these three chargers offer a range between 50 and 90 mA.  

How do you find out if your particular charger orphan will work on something that needs to adopt a charger?

Simple.just connect it to the battery pack you want to charge after checking the polarity to make sure that plus goes to plus and then measure the current with the digital multimeter I told you to buy and see if it is in the range you need. Remember that current will be flowing from the charger into the battery (unless you are trying to make a battery discharger which I don't recommend, as it may make the charger unhappy and the battery equally unhappy). The positive lead of the meter should go to the positive of the charger with the negative lead going to the plus side of the battery. Complete the circuit by connecting the negative of the charger to the negative of side of the battery.  

Let it charge for some time as the current will start out higher on a discharged battery and then taper off some as the battery reaches full charge. To be on the safe side keep an eye on the charger the first time you use it in its new role to make sure it is not over heating. Warm is OK. Hot (uncomfortable to hold) is a problem. UL approval would assure that the charger would not overheat but on the off chance that it may not have this approval, it's better to be safe than sorry.  

Not all of the plug in the wall chargers provide DC current required to charge the battery. They are just a step down transformer and will need a diode, or better a diode bridge, inserted as a rectifier to convert the AC to DC. The diode should "point" from the charger (either lead) to the positive lead of the battery. If you don't have the foggiest idea of what this is all about don't mess with it or get one of your electrical buddies to

give you a hand. You can't get into too much trouble, as this is very low voltage stuff. The Ni-Cd pack, on the other hand if you have not already discovered it, can do a number on your wiring harness if you get things mixed up and short it out.  

There are a couple of great chargers no longer on the market that you should keep your eye out for at flea markets. The Ace H/D500 is a nice variable constant current source that will handle anything up to and including a 12-volt battery charging up to 500 mA. For twice the fun a dual unit (Model DMVC) is available.  

These handy units can form the heart of a charger characterization system. Connect it across 2 10 ohm 20 watt resistors in series. Vary the current to set the voltage across the resistors to represent the voltage of a Ni-Cd pack under charge (1.35 volts/cell). Then connect the charger you want to study across the same resistor string. The charge should be passing current through the string in the same direction as the current source. By varying the current source and switching one of the 10 ohm resistors in or out of the circuit you can cover quite a range of charge voltage/current situations and plot what the test charger is capable of. You must make provisions to measure the voltage across the resistors and the current coming from the charger under test. By this time you should have gone out and bought that digital multimeter before they are all gone.

CLS 4-93 rev 7-03

Notes:

The "wall wart" chargers while designed to charge a specific number of cells at a specific current. This is usually the rating seen on them. The consist of nothing more than a transformer, and a diode to rectify the AC input. The windings of the transformer are designed to have the necessary resistance (or some resistance may be added) to set the current at the right level for the specified number of cells. In actuality, because a true constant current source would be quite expensive, the "wall wart" is a compromise in design. If you were to measure the voltage without being connected you would find it is somewhat higher that the voltage of the battery to be charged. A Futaba charger for instance, measures 6.7 volts* at the receiver plug, while it says the voltage is 4.8 volts and current is 50 mA. Even his really not true as the current is around 60 mA at the beginning of charge and then settles down to 50 mA as the battery reaches full charge and the voltage approaches 6.0 volts. This is how you can use a "wall wart" charger marked for a specific voltage/current on a battery with more or less cells (voltage). You just have to make sure that the resulting current at the higher or lower voltage is proper for that battery. A simple current measurement while on charge will take care of this.

*keep in mind this is an unfiltered half wave voltage measured on a digital volt meter, so not actually a true DC.  return to welcome page    

 See the Lithium-polymer safety comments at the end of this document.By Simon Van Leeuwen, Calgary, Alberta -   RADIUS SYSTEMS e-mail  lomcovak@telusplanet.net April 2002

As opposed to crying wolf here, lets take a look at what the Li-Ion technology really is. I spoke at length recently on this list regarding 7.2V LG Chem 18650 Li-Ion 7.2V packs looking for interest from you the (narrow or specialty-market) consumer. I have in hand ~100 of the LG Chem cells, through industrial testing on a contract I managed. Recently a company has  introduced Li-Ion to the modeling public offering various tapped voltages. I suspect that others will make their presence known shortly most likely using the manufacturers I have mentioned here and previously.

All pack builders who legitimately acquire Li-Ion or Li-polymer cells are obliged to install protection circuitry that matches the cells characteristics. Depending on the pack builder and their reputation, this may be required in writing! The two main reasons for this are cell integrity, and safety. One could argue which is more important, but it is really academic.

Given the nature of our application, and the inevitable risks associated with supplying Li-Ion packs with or without protection circuitry, is a double-edged sword. For me to supply packs to you without protection circuitry, means I would make each and every one of my customers legally sign off to hold me harmless. I personally would have it no other way. In the world of legalities though, this STILL may not save my butt if something untoward were to occur. I think my reasoning will become evident as I continue. To supply packs WITH onboard protection circuitry, requires you the consumer to understand that it is not such a bad deal. For starters, all issues regarding overcharge, switches left on, and over-current that would cause problems anyways, are no longer an issue. The over-current thing will be discussed further down (phew...sooo much writing ahead).

There are lots of quality battery pack builders across the continent. However there are very few who are willing (and competent enough) to supply current technologies with higher than average current delivery abilities. One has to keep in mind the intended market (which is HUGE) for these relatively new technologies; cellphone/pagers, laptops, PDA's, PCS's, and a host of other new enduser technology. These systems, although relatively power hungry, do not have current demands on the order of what WE are making them do! One look at the nominal specs will confirm this. Anyways, I was lucky enough in my investigations to find such a company, and I think you will find the following information I absorbed interesting:

Lets talk about Li-Ion cells, specifically the 18650 series that I proposed a while back for our use. These are cylindrical, and weigh ~43g each. There would be 2 parallel packs,

wired in series to create 7.2V nominal. For the record, I would not have suggested these cells if I did not believe they would work in even our most demanding scenario to date. For starters, every 18650 regardless of manufacturer has a PTC (Positive Temperature Coefficient) installed under the + button during cell manufacture. This is not removable without destroying the cell. A PTC reacts to temperature elevation by reducing current flow and can be chemically altered (during manufacture of the component itself) to trigger at different temperatures. However, this is not an exact science, and as a result there is a relatively wide window as far as tolerance goes on these devices ( I have used these in circuits and can attest to this I assure you).

In essence, a PTC can reach a specified undesirable temperature and begin to reduce or stop current flow in an attempt to reduce temperature. Known as polyfuses (remember the last time I mentioned these??), these devices will literally stop current flow (to uA anyways), and require removal of the load and must allowed to cool down in order for them to properly reset, to again allow initial specified current flow. Kinda like a self-resetting fuse if you will. This is is an undesirable characteristic when it comes to batteries in general, and specifically our situation.

To get around this, the battery manufacturers install PTC's so that they are compressed or "squished", altering their chemistry and therefore their function. What this does is limit the current flow, but does not stop current flow. The degree to which they are compressed will have a great bearing on HOW much (maximum) current will flow at a given temperature. Now, given that there will always be minor inconsistencies from cell to cell as they come off the assembly line, requires a warm body to test samples out of each batch to determine that indeed the PTC, amongst other things, will operate between a set range of values. In other words, one cells maximum current delivery will be slightly different then another! No biggie, but chew on it for a moment.

Then there is the fact that cells are paralleled, then these 2 are connected in series with another 2, to come up with a nominal 7.4V. No matter HOW precise cells are manufactured, and no matter HOW linear one cell is to its brother, there ARE inconsistencies! What this equates to is as the pack ages, individual cell performance will not be linear compared to it's counterparts within the pack. We have already seen how this can adversly effect pack performance if some sort of measures are not taken to monitor/tune up each and every individual cell periodically. Sounds bad...doesn't it? There is no cell-mathcing going on that I am aware of that would minimize this. Then again, cell matching might not initially show actual cell performance to the degree that enhances consistency! Welll, maybe by the time this type of inconsistency rears it's ugly head, the pack will be near or at EOL (end of life). Something else to chew on. Li-Ion is dangerous as someone else has pointed out. The risk of fire or explosion is real (remember what I said about getting you the consumer to sign off for me?). If for some reason a cell reaches ~130C, it tends to go into thermal runaway. That is, it no longer requires current flow to prevent the internals from turning cherry-red and either catching fire or exploding. The last defense to prevent this is what are called shut-down separators that are strategically placed between the anode and cathode (reactive materials - one in this case Lithium). The shut-down

separators are made of a plastic-like material which is normally porous, allowing ionic flow (ion flow is the process by which the battery allows us to charge and discharge - supplying us with the energy to fly our aerobats). This material literally melts, sealing off it's porous structure, hopefully preventing ionic flow and stopping catastrophic failure. No ionic flow inside the battery, no electron flow outside the battery. Don't chew on this one too hard, your might burn your mouth.

As a side note, prizmatic (rectangular form-factor) cells do not have the PTC internally installed, but are still required to be welded externally during the pack building process. The prizmatics can NOT supply the same power as the 18650's.

Incidentally, I was talking to our supplier and asked if indeed the LG was the best out there. One of their engineers really enjoys his job, and as a result is infinitely more knowledgeable than I will ever be. As opposed to adhering to the cell manufacturer's recommendations religiously, he has (with their blessings) moved into no-man's land and really "exercised" these technologies. Things like controlled shorting to see what current IS available with and without the PTC in place. A couple of cells stood out over even the LG Chem. The Samsung and Moli's demonstrated excellent comparative internal resistance against the LG cells. In the real world though, the cells we will get will have the PTC. These two marques also demonstrated better performance WITH the PTC. Then again, if during production the PTC had been squished too tight, this could account for the extra current handling abilities. Needless to say, the target is always moving as cell manufacturers are coming up with better ways to lower internal resistance, which in turn will allow greater current flow, which will in turn minimize the amount of protection circuitry required in the first place! Which brings up the next topic.

The statement I have heard (even from the "experts") most often is "I would much rather have the pack kill itself and allow me to land my aircraft, than have it shut off on it's own accord". I propose with properly designed onboard pack protection circuitry, the point at which the pack would die is slightly below the point at which the circuitry would shut down. However, given some variables, we can only get part way there (I would be writing till the cows came home if I go down this path). Then again, one needs to look at just what would be gained by having a pack kill itself in order to "save" an aircraft. That in itself is a topic worthy of REAL discussion! The concept of a pack sacrificing itself to allow a successful landing, would be speculative at best. However a nice conversation exploring onboard circuitry I suspect would result in a thought change that would make it a viable and acceptable component to compliment exotic(?) battery technologies. The empathy bridge has already been crossed on a number of other fronts, most recently NiMH cells, matchboxes, onboard power distribution busses, regulators, electronic RX switches, microprocessor-driven TX's, servos, and ignition systems, autopilots...the list goes on.

The onboard circuitry their engineer and I are working with (their in-house offerings) will allow the following (using LG Chem 18650's):

-4Ah, 7.4V nominal, 8.4V max, 5.6V min. -6A continuous, 12A peak with an RC constant that can be extended depending on application. -~200g (7oz) total weight

The above scenario uses 2 protection circuits per pack to get the minimum current demand I proposed. Onboard smarts does more than just limit max current (I). The canned circuitry also monitors charge V, low V cutoff, continuous I, instantaneous short protection, and max current that has an adjustable time constant to allow I peaks of selectable duration to address unique load needs. He has worked with another manufacturer's onboard circuitry that will allow even larger constant/peak current demands, but would cost more. All the circuits are "very" reliable, consisting of controlling 2 or more high-current FETS (Field Effect Transistors). The reliability is as much a non-issue as it is with our TX, RX's, servos, etc.

At this point, for me, what makes the system (sorta) viable on large aircraft is the idea of 2 of the above mentioned packs, with protection circuitry, operating in parallel, feeding 4 pigtails from 2 packs into 2 Rx's. That equates to 8Ahrs, 20A+ on demand, with single drop-out redundancy to 12A, which you would probably notice during flight, for total mass of around 400g (14oz).

Now for the fun stuff. Due to the relatively high internal resistance associated with Li-Ion, under load the voltage O/P drops significantly. This is sorta OK, as it occurs with all other cell technologies we are using (NiCD offering the lowest internal resistance therefore lowest V-drop - which is better for our needs as current demands change drastically).  It is possible to have the onboard circuitry get messed up though. A pack that is reaching EOL, if asked to deliver a large amount of current, may exhibit V-drop to the degree that the onboard circuitry (OBC from now on!) will think the pack has reached it's discharged state and temporarily turn off, or stay off. Thing is, if you are running that close to the bottom on that aged a pack, maybe you deserve what you get! How do you decipher adequately EOL to avoid this. No one has done testing to the degree that will make Joe modeler comfortable I believe. But these are just the types of things that someone as a retailer/supplier has no control over. Using these types of technology can be equated to giving your dad (who has driven an Olds all his life) an F-1 car as a daily driver. It ain't goin' to last long.

Which brings up my next point. Although I relish new technology, it has to serve a viable purpose by demonstrating that it is indeed a better mousetrap than the one I am using now. Frankly, from a CPV (computer's point of view - I use this term often to demonstrate the idea of a non-emotional, purely logical decision-making process) no new battery technology has demonstrated enough of a change over what we are using right now (which in itself continues to demonstrate performance gains on par OR BETTER than all other battery technologies) to warrant switching. The only area where current technologies has an advantage in our arena is mass. Which brings up my next point.

Although I find the issue of mass to be inconsequential on large aerobats, there is some weird marketing thing that makes it the selling point, and quite possibly lucrative. Lets face facts, a blind test to determine if an "expert" pilot could determine even 6 times out of ten that aircraft "A" or "B" had 1.0Lb difference due to battery mass is beyond reason. Anyways, it's beyond me.

Finally, I think Li-Ion would market well on the "regular" model aircraft front, the major obstacle being "if it ain't broke, why fix it mindset" as it relates to Nickel Cadmium technology. I mean really, current technologies still have a long way to go to beat the all-round performance of today's NiCD offerings. In my electrics, modern NiCD's are supplying in excess of 100 amps and can climb vertically out of site in a few seconds. NiMH as a changing technology is coming close, but it's internal resistance is going to keep it in second place until it matches NiCD. At that point, NiCD's will probably become obsolete.

Simon Van Leeuwen, Calgary, Alberta RADIUS SYSTEMS Cogito-Ergo-Zoom IAC25233*MAAC12835*IMAC1756*LSF5953*IMAA20209 lomcovak@telusplanet.net

4/17/02 p.s. I have posted this site before, but it seems appropriate to point people to it again: http://battery.rnd.lgchem.co.kr/english/doc/main.asp

Lithium Safety – by Fred Marks (as posted on RCU - Battery Charger forum).

In order to present as clear a picture as possible and to guide in the safe use of Li pos, no matter the manufacturer, you will find at www.fmadirect.com under the Support section the Kokam Battery Systems Ap Note, Ap Note # 2 in pdf to download.

The following is a brief supplement to the Charging and safety sections of the Ap Note. The principal things to remember: Li Ion and Li Poly cells have Lithium in them and that is why they have five times the energy density of other chemistries. Powdered Lithium, if heated sufficiently, can ignite and burn. Understand: we can test, report, educate, add in any kind of safety device but, as long as Li is present there may be some way that it might be ignited. In the ultimate, suppose a lightning strike hits your model! The only thing to do in all this is to charge the packs in such a way that, if they do ignite, no harm is done.

Please do take time to read the following and download the information in the Ap Note.

All high energy density batteries including Ni Cd, Ni MH, Li Po, and LI Ions and the chargers used require common sense and caution. If any are overcharged or shorted, great heat and pressure result. Ni Cd and Ni Mh cells have a mechanism to vent excess gas

pressure, as do Li Ion cells. These cells all have in common, a thin metal can enclosure. I have experienced explosion of Ni Cd cells when the vent did not function properly. One such occurred at 1 AM in a deathly quiet shop as I worked on an Army radio system in 1984. That was behind me and about 15 ft away. You probably never saw a 55-year-old, 225 lb guy clear a 4 ft workbench flatfooted! I didn’t even bother sending the 4AH cells back to Sanyo since it was a charger malfunction that caused the event.

Li Ion cells truly can explode as they are sealed in a metal can. They too have vents. However, Lithium is a metal that, as a powered material can burn if ignited. This is true of several metals, not just Li. Magnesium burns readily even in solid form. Thermite is powdered iron that, when ignited, has been used to weld steel. Finely powered aluminum is the “fuel” for almost all solid rocket motors. Some solid rocket motors are made of extruded nitrocellulose, an organic material. Organic materials burn when ignited, just like paper. Powdered, sintered nickel takes a very high temperature to ignite.

Li Po cells also can vent if charged at too high a voltage. There is a narrow range of choice of the electrolyte for use in Lithium Ion cells. Remember that Li Po cells are a form of Li Ion; they derive their name from the fact that Li Po cells are housed in a plastic (polymer) envelope. If the envelope has a small Vee cut in the join line, that serves as a vent. The major difference with Li Po is that the envelope can swell when pressure builds to form the infamous “silver sausage”. Any cell is ruined when pressure that causes venting is experienced.

If a Li Ion cell suffers ignition, the vent cannot act quickly enough to prevent rapid pressure build up. When this happens, the can fails instantly and catastrophically just as it can in a Ni Cd/Ni MH if the vent does not function properly. The pressure release is, therefore, explosive just like popping a balloon only with massively more force. This is why all Li Ion cells used in OEM applications such as cell phones have a protective circuit on them.

The failure mode that leads to explosion in a Li Ion leads to an event called “venting with flames” in a Li Po cell. The basic phenomenon is called thermal runaway. If, say, a Li Po cell is charged at six to seven volts, well above the nominal 4.2 V limit, the electrolyte can begin to “boil” and develop voids as temperature rises above about 180 degrees F. If this abuse continues for, say, ½ hour, the electrolyte, being organic, can eventually ignite. As we said earlier, it takes a lot of heat to igniter Lithium. In a solid rocket motor, ignition is initiated essentially by a high explosive blasting against the propellant.

If the thermal energy release of the electrolyte used is high enough, the Lithium can be ignited. In tests I have conducted, the electrolyte burns at about the intensity of burning paper when it has a heat gun blasting it. When I light the fireplace I winter, I wad up newspaper in softball size wads and put in a layer before I put wood on the grate. If I have light, dry kindling, just igniting the paper with a lighter lights the fire. Last winter was so nasty that we ran out of kindling. I found that the thermal output of the wadded paper could be increased sufficiently to ignite reasonably dry maple logs by blasting the

paper with my Monokote iron. The point: Subtle but significant changes can affect ignition. Not every overcharge event causes ignition.

If the lithium ignites, it burns with an intensity and gas generation that can cause “venting with flames” that is the gasses exit the envelope with a swoosh, not a blast. If you have the pack in your airplane when this happens, your airplane is going to be damaged. If you have the pack on a highly flammable car seat, the seat is likely to catch fire.

Does this happen often? Not really; we have about a dozen such events reported in the past 18 months out of perhaps 100K cells in the field and, probably, a million or more charges. In all instances, analysis of the event has shown that the cell/pack was charged at too high a voltage and/or there was a fault in pack assembly.

Methods that are as stress-free as possible that permit one to use Li P cells in a completely safe way are outlined in Ap Note 2 located at www.fmadirect.com.  Open the home page, click on Support then scroll to Ap Notes to open or download the pdf file for Kokam Li Po battery Systems.

It is a simple matter to operate safely. Just as you are asked to avoid smoking while handling an open can of glow fuel, keep your hand out of the prop, don’t whittle toward yourself, and don’t fly while drinking, it is suggested that the simple warnings posted at our web site be followed. Remember, safety is a matter of discipline. Remember also, that we take care to educate the user about these things.

Fred Marks 11/30/03  

 Nickle Metal Hydride - the picture today.

The Ni-MH that are available to us today from Sanyo/Panasonic may be treated essentially the same as Ni-Cds –EXCEPT FOR PEAK CHARGING. You have to be careful here. Some chargers will accommodate them, others won’t - and end up severely overcharging them to the point of destruction.

In a given cell size Ni-MH has on the order of 20 to 30% more capacity than Ni-Cds. They have slightly higher internal resistance, but not enough to concern us in most R/C control applications. This higher internal resistance can be of concern in electric flight operations where it is common practice to add an additional cell to compensate. They have a shorter cycle life in general, but again not enough to be of real concern. Most people run out of calendar life before cycle life in flying R/C. Meaning that the separator system in the battery (same for both types) fails (shorts) before the cells fade away in capacity delivery ability. Ni-MH are less tolerant to abuse (excessive high rate discharge, excessive overcharge, vibration, cell reversal) than Ni-Cd – but again, it seldom becomes an issue if reasonable care is given in the installation and maintenance of the packs.  Ni-MH capacity falls off with cycling whereas Ni-Cd stays pretty constant, seldom going

below 80% before shorts develop. Ni-MH has a higher self-discharge rate  (3-4%/day) than Ni-Cd (1%/day). Ni-MH cost a bit more per Ah of capacity.  

Red S. Red’s R/C Battery Clinic http://www.rcbatteryclinic.com

Updated 2/04

HUGHES SPECTRA 4 - A charger for all reasons.

Remember when the Litco Alpha 4 was the hottest item in charging? It was so hot that you literally had to win the Litco raffle to even get one and then be willing to part with $300. This bought you the capability of charging 4 different packs at the same time. While the Alpha 4 has essentially disappeared from the market the need to charge/cycle various kinds of packs has not. Hughes R/C www.hughesrc.com has stepped forward to fill that gap. While there are other multiport chargers available, few if any give you the charge/discharge/cycle control offered by the Hughes Spectra 4 for all the battery chemistries we are now employing. One of the first things that strikes you when you get the charger, is the size. This is not a wimpy little charger that you can lose on your charging bench. Its commanding appearance with large heat sink on one end says serious charging. Turning it on the first time is another surprise as the display after displaying the Hughes welcome statement with firmware version, scrolled to “Property of Red Scholefield, Newberry, FL (352) 331-8410. The people at Hughes program the owners information into each charger sold and can change it if the original owner requests it.

Hughes Spectra 4 charges different chemistries all at once.Specifications:

4 Outputs - Manages up to 4 batteries at one time 1-10 cell NiCad / NiMh1-4 cell LiPo / Li-Ion / A1231 - 6 cell Lead AcidCharger / Cycler */ Loaded Volt Meter *cycling for 2 or more cells50 mA – 1000 mA per port (Charge or Discharge) Input 11-15 VDC80 character 4 line backlit LCD displayReverse Polarity Protection on Input and OutputMemorizes up to 20 battery pack charge settings for “AUTOCHARGE”Remembers packs by NAME not NUMBERCharges Multiple Batteries with Common GroundsSimple 4 button operation, menu drivenDetailed monitoring of all ports

Audible alerts Battery Backup in case of power failure Built in Loaded Volt Meter Fast charge with peak detection (selectable rates) Timed charge (selectable rates) Topping charge option (selectable rates)Trickle charge option (selectable rates)Accurate battery management Rugged all metal enclosure 1 Year Warranty Memorize up to 20 battery pack charge settings for"Automatic Charging" Weight: 2 lbs.Size: 8” X 5” X 3”Remembers packs by name not just by a number Each pack name can be up to 16 characters long Memory Examples:Futaba TXExtra 300 RX CAP 232 ignition

All of the charge parameters measured and recorded appeared to be well within the accuracy limits expected for this type of equipment.

Display features:The ample display gives you all the information about the pack. Figure 4 shows the END display for 3 cycles on a 4 cell Ni-Cd pack that had a one flight on it in the morning before cycling. P3 is for Port 3, CYC indicates there were 3 cycles, the last charge was 1 hour 7 minutes 33 seconds with 736 mAh input. The readings at the bottom were for the capacity delivered on each discharge. The Spectra 4 discharges then charges in the cycle mode.

Battery Back-up Feature.The Spectra 4 is shipped with a battery backup lead. Just connect a 7.2 to 12 volt Ni-Cd or Ni-Mh pack to the jack on the left end near the power wire. In the event of a power failure, the backup battery will continue to power the microprocessor and LCD while terminating all other functions. When power is restored, all functions will pick up where they left off. Battery backup can save you a lot of headaches, especially if you are powering your unit from an AC driven power supply, subject to the power company’s reliability. Your backup battery pack does not need to be large. A 500 mAh pack should keep you going for more than 10 hours of power failure. When you are doing multiple cycles, battery backup can keep you from having to start over.

Need more power?Just connect 2 or more ports together with simple to make harness (detailed at their web site) and you can charge/discharge up to 4 amps for a single pack, or 2 packs up to 2

amps. Just set the ports to the charge amount you want to add together. If you want 3500 mA, set 3 ports at 1 amp and one at 500 mA.

A caveat for all chargers.This is the first time I’ve seen this admitted by any charger manufacturer. From the Hughes Owners Manual “Batteries should be disconnected from the charger within a reasonable period of time after all functions have been completed. Once “END” is displayed there will be a small discharge (less than 5 mA) on the battery.” I knew this was the case with some chargers like the old ACE DVMC. But my curiosity was aroused so I checked a number of other chargers in the lab. EVERY ONE PUTS A SMALL LOAD ON THE BATTERY WHEN THE CHARGE IS COMPLETE. So if you are using chargers that do not have a continuous or pulsed trickle charge you could find a pack somewhat discharged if left connected to the charger for an extended period (4 or 5 days for a 500 mA pack).

ElectriFlyTRITON PRODUCT REVIEW

BY Red Scholefield – Red’s R/C Battery ClinicGreat Planes raises the anti in the $100-$200 charger range with their introduction of the Triton.Behind the distinctive red plastic bezel the extruded aluminum case contains some innovative features. As the hobby standard Ni-Cds are being challenged by newer technology offered by Ni-MH and now Lithium-Ion/polymer systems, the Triton presents a battery maintenance system that addresses these new offerings.Item Tested - Triton Computerized Charger, Discharger, Cycler

Purpose – Battery Maintenance SystemManufacturer – Great Planes

Suggested Retail Price – $129.99

Warranty – One yearInput Power -10-15V DCCharge Range – 1- 24 Ni-Cd or Ni-MH, 1-4 Lithium Ion/polymer, 3-12 Pb (lead acid)Fast Charge Rate – 100 mA to 5A - 90 watts max (2.5A max. for Li-Ion/polymer) Trickle Charge Rate – 30 to 250 mA – automatic (n/a for Li-Ion and Pb) Discharge Current - 100 mA to 3A - 20 watts max (2.5A max. for Li-Ion) Discharge Cut-Off - 0.5-1.16V/cell NiCd & NiMH, Li-Ion/polymer 2.8V/cell, Pb 1.8V/cell Cycle Count - One to ten cycles (n/a for Li-Ion/polymer and Pb) Battery Memories - 10

Dimensions – 6.2 x 4.0 x 2.0 in (157 x 102 x 51mm) Weight - 16.4 oz (466g)

Instructions –19 6 X 8 ½ pages – plus 5 program flow charts.Tested On – Ni-Cd, Ni-MH, Pb (lead acid), Lithium Ion/PolymerCHEERS – The broadest range of battery types served. Programmable voltage cut off, peak sensitivity, topping charge and safety features. Banana plug connections on the SIDE of the charger where they belong so as to not obstruct the display or controls. Once you are over the initial learning curve, which is about the same as other units, the Triton is faster to program.

JEERS – Programmable trickle charge and an on-off switch would be nice. Lithium charge rates based on very conservative protocol may not fully charge lithium packs.When in doubt, read the directions! For a preview of the details of how this unit works, the instruction manual may be downloaded from: http://www.electrifly.com/manuals/gpmm3150-manual-v1_1.pdfFor reasons known only to the instruction book authors, charger purveyors feel bound to comment on the “Nickel Cadmium memory problem” and what their unit does to address it and well as perpetuating other popular battery myths. The Triton instruction manual is no exception. Just ignore it in that regard, you won’t buy the Triton for the literary value of the instruction book, but rather to maintain your battery packs. This is accomplished quite nicely with the aid of the five programming flow charts that were thoughtfully included with the product.Once you have the basics down these programming charts are all you need for future reference.

Cooling FanInstruction book states that the Triton will shut down if internal temperatures exceed 100° F. This is in error and should read 100° C.Great Planes technical people have clarified the fan operation: The fan does not turn on until needed, which occurs in the following circumstances:     1. During discharge once needed.     2. During charge: a. if the temp of the charger exceeds 50 degrees centigrade b. if the charge output power is over 30W c. if the charge current is over 2.5A d. if charging 1cell, or packs containing 2 or 3 cells    

3. During charge or discharge, if the temp of the charger itself exceeds 100 degrees C the charger will stop all charge or discharge functions unitl the temp of the charger becomes below than 70 degrees C. The fan should continue to run unitl the temp of the charger drops below 45 degrees C. (We cover this in the manual)     In addition, once the fan turns on it should work until the charge or discharge function is finished. If the temp of the charger still exceeds 45 degrees C after a function is completed the fan should continue to work until the temp drops below 45 degrees C." <!--[if !supportEmptyParas]--> <!--[endif]-->

TestingWe ran the usual performance tests on this unit using a digital multimeter with an RS232 port connecting to a laptop. Old as well as new packs ranging from single cells to the maximum of 24 were tested. Dozens of charge/discharge curves covering all the settings were accumulated. Charge and discharge curves (Figure 1) obtained from a well used 7 cell Cs electric flight pack are typical.Figure 1. As the curves indicate, the Triton employs voltage-sampling techniques that are pretty well standard in chargers of this type. Suffice it to say that the testing verified the manufacturer’s claims and found them to be an honest representation of the unit’s performance and capability. Voltage and current readings were within 1% of those indicated by the unit.Based on time and discharge currents the capacity readings were also well within reasonable limits for a unit of this type. Neat Features: The people at Great Planes tried to cover all the bases and did a pretty good job. If the buzzer annoys you it can be turned off – or set to any of 10 different melodies.

But they considered some serious things also. Two backups are provided in case the charge termination scheme doesn’t do its job. You can set a Safety Timer and the Max Charge Input (in Ni-MH mode). If you are still timid, a Thermal Sensor is available as an accessory, which allows you to program the Temperature at which you would like the charge to terminate. This reflects an understanding of the real world of batteries rather than distrust of the system’s ability to terminate charge. To address the problem of early or premature peak shut down they give you a programmable Peak Delay as well as the ability to set the Peak Sensitivity. If you can’t get enough flying in to wear out your batteries the Triton lets you cycle them up to10 times automatically and keeps the capacity in/out readings for each cycle. You have the option of Charge then Discharge or Discharge then Charge. Many peak detector chargers don’t provide the needed trickle or topping charge needed to balance out the pack after it peaks. The Triton has taken care of this with a default Trickle Charge based on the charge rate selected and for Ni-MH, 20 minutes of programmable Topping Charge. There are 10 Battery Memories available to store your favorite set up. And for those that don’t have a clue there is an Auto function for most settings that has the Triton making all the decisions – and quite conservative ones. Per the instructions, auto mode is not recommended for smaller capacity packs. I don’t recommend the auto mode for any packs. With all the programming functions at your disposal why let the charger have all the fun making decisions? When used, the auto charge was very conservative and did not set up charge rates that would be satisfactory for electric flight (or your transmitter/receiver packs) field charging where a fast turn around is required.Pushing buttons – when and when not to. The first thing that strikes you on this unit is that it has two buttons and a combination rotary dial/push button, unlike the 4/6 button arrangements seen on competitive units.I would have to temper the marketing hype, “amazingly easy programming in almost no time”, to “it took me about as long to get comfortable programming this unit as it did others I have tested”. Thanks to another modeler, Darral Teeples <hdthc@juno.com> that was also working his way through the amazingly easy programming, we collaborated, comparing notes on the Triton’s operation secrets – when our notes did not agree we isolated the problem to a slow switch (unit immediately replaced by Great Planes) or in another instance to a low battery in a DVM (that’s what that little flashing battery symbol means).When you first connect the Triton to a 12 volt source you get a few seconds of“GREAT PLANES ELECTRIFLY” then it goes to the charge mode and rate of the last battery type you used with all of the settings you had programmed for it.If this is what you want to do you simply depress the rotary button for a few seconds and the charge process begins.If you want to change any of the setup, depress the MENU button and rotate dial to what you want to set, press the dial momentarily and then rotate to the setting you want, pressing the dial once more to the setup where you can rotate to move to the next item. Once you have made the any changes to the setup press the MENU button again to go to the charge mode. Five battery types (Ni-Cd, Ni-MH, Pb-lead acid, Lithium or one of 10 battery memory setups) are selected by the BATT TYPE button, where you can then set one of the 4

routines (charge, discharge, charge then discharge, or discharge then charge) with the rotary button. Individual settings with these charge rates, discharge rate etc. are set by pushing the rotary button momentarily and then dialing the rate you want. It is actually simpler to do than describe. Just follow the Programming Flow Charts. Once you get use to it, the Triton is easier to program and is certainly faster with the rotary dial feature to scan back and forth in the various display screens.

Fooling the “Smart Charger”While they tell you some of the features are available in the Ni-MH mode only, you can cheat a little. Just set up for Ni-MH (set the peak sensitivity for 10 mv) and then connect your Ni-Cd battery and start the process. The Triton, smart as it is, cannot tell it is charging a Ni-Cd and will allow you to use all the Ni-MH features.Screw up protection. Both input and output have reverse polarity protection and in the case of the output connection gives you an error reading to inform you of your sin. It also features an internal thermal protection that shuts the unit down with an Overheating display if the unit internal temperature exceeds a 100 degrees F. I didn’t check this out but heard one user complained that where he flew it frequently got over 100 degrees – maybe Triton had the good sense to warn the user as well as protect itself. Overcoming the DC only stigma.Many chargers are being offered that operate on DC only, while limiting them to 12 volts overcomes the onerous UL certification process, many find that this restricts the utility of the product. One does wonder how many people actually use the full features and capability while the unit is connected to their car battery.The thought of having to purchase a separate DC supply at $40 or more to use the cycler in your shop is not appealing either.There is an inexpensive solution. It is found in the power supply of your old PC, or if you don’t have an old one laying around you should have trashed, you can get one at most any PC repair shop just for carting it off. Once you have rescued the power supply drop by the Battery Clinic www.rcbatteryclinic.com where you will find a link to Pat Harvey’s excellent article on the conversion details hosted by the Minnesota Area R/C Electric Flight Enthusiasts. The Triton may not be the ultimate in chargers in this category, but it comes as close as the reviewer has seen to date.  <!--[if !supportEmptyParas]--> <!--[endif]-->Red Scholefield red@rcbatteryclinic.com 12-14-02 Rev 12-21-02

Setting Up a PC's Power supply to use with your Dc/DC battery charger

By Pat Harvey

Most of us have several battery chargers for our NiCad packs. Most of these chargers only operate on 12 volt DC inputs (your car battery). This is fine as long as you are at the flying field. This isn't so fine when you want to cycle a pack on the workbench or peak up a pack before you leave for the field (and the wife

has the car). We have all had the need for a good source of 12 volt DC power, good clean power. I had a couple of simple power supplies but one of my chargers would not run on either of them.

The power supplies from old PCs will provide good clean power that will run either (as well as both concurrently) of my chargers. One charger is an Astro 110D and the other is Dymond Super Smart Charger. If you have the need - Let's get started. The basic tools you will need are a VOM, screwdrivers, soldering iron, wire cutter, pliers, drill and bits.

The first thing is to get an old PC power supply. If you have an old machine setting gathering dust that you should have thrown out, you are in luck. If you don't have one, then stop by the local PC fix-it shop. Often they will have machines that are destined for the dumpster that have perfectly good power supplies. Just offer to haul the whole thing off for them and you may have a real bargain. If you can't get one for nothing, then many shops sell used power supplies at a fair price. I've had very good luck in getting free ones.

Open the PC case and take a look at the top of the power supply box. It will tell you how many amps at +12 volts are available from this power supply. It should be at least 4 amps to be of much value. A 7 or 8 amp output on +12 volts is very common and if this box is too low power you may wish to look for a different power supply. In order to take the power supply out of the case do not cut any wires, simply unplug everything. Once you have the power supply out of the PC case, you have to decide which of three basic types of power supplies you have. If the switch for the power supply is a paddle switch on the side of the power supply itself you have an older AT style power supply. If it is a push button type switch, either on the side of the power supply or on an umbilical cord them you have a newer AT style power supply. If it only has a "rocker" type switch (or no switch) it is probably an ATX style power supply. The label may in fact have "ATX" on it. An ATX style will have a plug that goes to the motherboard which has a double row of connections with 10 connections on each side. Only bother reading the section that follows that applies to your style of power supply.

Older AT Style Power Supply (the ones with the paddle switch on the side)

You are in luck. This old style power supply (PS) is much simpler to make work and generally the case is larger so you have more room to work. Plug in the power supply and turn it on. The fan should be running. Use your VOM and identify the correct color pair of wires for +12 volts. This is fairly easy. Pick a set of wires that ends in a plug with only 4 wires. This probably went to a disk drive (either hard disk or floppy). There will be 2 center wires the same color (probably black) and the outside wires will be different colors (perhaps yellow and red). Use the VOM with one probe in a center wire and one probe in an outside wire. What you will find is that the center wires equate to a negative post on a battery and the outside wires are the positive posts. With enough trial and error you can identify most of the colors. Ones that I have seen are:

Yellow +12 volts

Black Common

Red +5 volts

Orange -5 volts

Blue -12 volts

White Power good .

There will be a lot of +12 volt wires, a lot of +5 volt wires, an awful lot of "Common" wires and only one or two -12 volt or -5 volt wires. Normally there is only one "Power Good" wire.

Now that you know which color is +12 volts and which is "Common" all you need to do is "design" your box. Since we plan to use this power supply as a substitute for a car battery I envision it with "Positive" and "Negative" posts, just like a battery. Pick two locations on the PS case that will allow your charger to be clipped onto without shorting out, and that you can run several wires to the inside of the PS case to those locations. Go to the local hardware store and get:

2 rubber grommets (1/4 inch center holes is fine)

2 #10 machine bolts 1 1/2 inches long (these should go through the grommets without problem)

4 nuts for the bolts

4 flat washers for the bolts

4 large (probably 1/4 inch by 2 inch diameter) nylon (or other insulating) washers with small (1/4 inch) holes in center

Now back at the shop. If you happen to have some Red Zagi tape and some Black Zagi tape then cover one side of a Nylon washer with Red and one side of another Nylon washer with Black. Trim the tape from the uncovered side with a sharp knife. Drill a 5/16 hole at each of your chosen locations. Put a rubber grommet in each hole. Next cut 3 or 4 of the +12 volt wires to length to reach the first hole. Solder these wires to the bolt (near the head). "Ring terminals" are an excellent option rather than soldering directly to the bolt but either route will work. Put a nut on the bolt and tighten it against the soldered wires. Put a metal flat washer on the bolt. Next put one of the nylon washers on the bolt. Shove the bolt through the grommet. If necessary you can trim the nylon washer a bit if it conflicts with something but leave enough of the nylon washer to be sure the wires do not contact the PS case. Put another nylon washer (the Red one if you covered one with Zagi tape) on the bolt. Put another metal flat washer on the bolt. Put another nut on the bolt and tighten it up. You now should have "Positive" battery post that is fully insulated from the PS case.

Next cut 3 or 4 of the "Common" wires to length to reach the second hole. Repeat the same process you did with the plus 12 volt wires this time using "Common" wires. Use the Black Nylon washer on this one if you covered one with Zagi tape. You now have the "Negative" post for your new PS. Now all that is left is to cut off the excess wires such that they will not short out. Put the cover back on the power supply and mark the posts as "Positive" and "Negative". You are done.

 

Newer AT Style Power Supply (the ones with the push button switch on the side or on a cord)

This power supply (PS) is a bit more complicated than the older ones and requires a bit more work. Not only that they tend to be smaller and there is less room to work inside the PS box.

Plug in the power supply and turn it on. The fan may be running or it may just start and then stop. Generally the following colors will identify specific functions - generally:

Yellow +12 volts

Black Common

Red +5 volts

Orange Power good

Blue -12 volts

White -5 volts

Green or Grey Power Supply – On (PS-on)

Note: "PS-on" may not exist. If it exists it will be part of the double rowed plug that went to the motherboard of the PC.

If the fan is not running consistently turn the power off and temporarily connect "Power Good" to a +5 volt line. This should cause the fan to run consistently when the PS is turned on. If the fan is still not running you should look for the "PS-on" line and connect it to a "Common" line. The PS-on line is in fact a switch to turn on (or off) the PS. Use your VOM and identify the correct color pair of wires for +12 volts. This is fairly easy. Pick a set of wires that ends in a plug with only 4 wires. This probably went to a disk drive (either hard disk or floppy). There will be 2 center wires the same color (probably black) and the outside wires will be different colors (perhaps yellow and red). Use the VOM with one probe in a center wire and one probe in an outside wire. What you will find is that the center wires equate to a negative post on a battery and the outside wires are the positive posts. With enough trial and error you can identify most of the colors. There will be a lot of +12 volt wires, a lot of +5 volt wires, an awful lot of "Common" wires and only one or two -12 volt or -5 volt wires. Normally there is only one "Power Good" and one PS-on wire.

Make the connection from "Power Good" to +5 volts a permanent connection (solder it with a bit of heat shrink).

Now that you know which color is +12 volts and which is "Common" , next you need to "design" your box. Since we plan to use this power supply as a substitute for a car battery I envision it with "Positive" and "Negative" posts, just like a battery. Pick two locations on the PS case that will allow your charger to be clipped onto without shorting out, and that you can run several wires to the inside of the PS case to those locations.

You may wish to move the PS power switch into the case if it is an "umbilical" cord type switch. I normally choose to move it into the hole that the "umbilical" cord comes out of the PS case through. This process is just a matter of unsoldering the wires, shortening them and re-soldering them. Be sure to solder the right same colored wires back onto the same lugs on the switch. You will probably need to drill a couple of mounting holes in the PS case to hold the switch and mount the switch using these holes and a screw through each.

Go to the local hardware store and get:

2 rubber grommets (1/4 inch center holes is fine)

2 #10 machine bolts 1 1/2 inches long (these should go through the grommets without problem)

4 nuts for the bolts

4 flat washers for the bolts

4 large (probably 1/4 inch by 2 inch diameter) nylon (or other insulating) washers with small (1/4 inch) holes in center

A 12 volt automotive light with a socket and wires (I use a small clearance type light with amber lens). A #1154 or #1156 bulb also works well.

Now back at the shop. If you happen to have some Red Zagi tape and some Black Zagi tape then cover one side of a Nylon washer with Red and one side of another Nylon washer with Black. Trim the tape from the uncovered side with a sharp knife. Drill a 5/16 hole at each of your chosen locations. Put a rubber grommet in each hole. Next cut 3 or 4 of the +12 volt wires to length to reach the first hole. Solder these wires to the bolt (near the head). "Ring terminals" are an excellent option rather than soldering directly to the bolt but either route will work. Put a nut on the bolt and tighten it against the soldered wires. Put a metal flat washer on the bolt. Next put one of the nylon washers on the bolt. Shove the bolt through the grommet. . If necessary you can trim the nylon washer a bit if it conflicts with something inside the PS case but leave enough of the nylon washer to be sure the wires do not contact the PS case. Put another nylon washer on the bolt (use the Red Nylon washer if you covered one with Zagi tape). Put another metal flat washer on the bolt. Put another nut on the bolt and tighten it up. You now should have "Positive" battery post that is fully insulated from the PS case.

NNext cut 3 or 4 of the "Common" wires to length to reach the second hole. Repeat the same process you did with the plus 12 volt wires this time using "Common" wires. Use the Black Nylon washer on this one if you covered one with Zagi tape. You now have the "Negative" post for your new PS.

Next choose a location on the PS case to mount the automotive light socket. Mount the light and connect it to a "Common" wire and to a +5 volt (yes plus five volts) wire. You need a small "load" on the +5 volt side of the PS in order for it to put out it's maximum voltage on the +12 volt lines. Some folks use a 1 ohm 25 watt resistor. E-zone is full of opinions on this but I find a small load works fine. If you are not getting slightly over 12 volts of output on the "posts" you can add a second light by connecting it to a "common" and a +5 volt wire.

Now all that is left is to cut off the excess wires such that they will not short out. Put the cover back on the power supply and mark the posts as "Positive" and "Negative". You are done. The automotive light will serve as an indicator light that the PS is turned on.

 

ATX Style Power Supply (the ones with no switch or maybe a "rocker switch" on the side of the box)

The ATX power supply will have a rather long 20 pin plug that went to the PC motherboard that has the following pin-outs:

 

 

Note that PW-OK (or PWR_OK) is the "Power Good" signal.

Conversion of an ATX style power supply proceeds just like the conversion of the newer AT style units except that you can ignore the discussion about moving the switch. Please use those guidelines (above) with this exception.

Lithium Polymer Batteries is the favorite power source of electric radio-controlled models. They are relatively cheap, light, and hold lots of power. However, many new hobbyists may have some enquiries as to their operations.

Here are three frequently asked questions about them.

1. What is Cell Balancing?

Lithium Polymer batteries usually come packaged as a pack of more than two individual battery cells. For example, electric RC helicopters use 3-cell packs. Each of these battery cells has a nominal voltage of 3.7v; which means that each cell can operate when it maintains its charge between 3.0 to 4.2v. To go above or below or below this range can damage the cell and render it useless, or worse, become dangerously unstable and explode.

While the battery is in usage, the power drawn out of each cell is not equal. Therefore, at the end of each flight, the cells in the battery will be left out of balance. A non-balancing charger will stop charging the battery pack once the voltage of the overall pack is full without paying any attention to each cell. This causes the battery to be more and more unbalanced with each charge and would also result in a diminished performance of the battery pack.

A balance charger eliminates any unbalanced-cells symptoms of a battery pack by charging each cell individually; making sure that the cell's voltage remain balanced at the end of each charge. In essence, balance charger lengthen the life of the battery back and maximizes its performance as well as keep the pack stable and safe to operate.

2. What is C rating?

A lot of radio-control fliers quickly grasp the meaning of most of the battery-associated acronyms but one: the C rating. In fact, many experts have tripped over themselves trying to explain it. However, I've heard a graspable explanation of it from an old Chinese battery manufacturer/expert very recently. Which is: The "C Rating" is the number which you multiply to the capacity of the battery to get its discharge rate.

Still confused? Basically, a 1000 mAh battery rated at 1C will provide 1000 mA of power for 1 hour. On the other hand, if the same pack was rated at 2C, it would provide 2000 mA of power for 30 minutes.

3. How fast can I charge a pack?

Each Lithium Polymer battery pack has a different maximum charge rate. It is very important to never ever charge at a rating above the specified rate! Most batteries have a label that specifies this vital information. However, if the maximum charge rate is not specified, keep in mind that most Lipos are made to be charged at a rate of 1C. Which means a 1000 mAh pack can be charged at 1A and a 500mAh pack can be charged at 0.5A. Once again, never ever exceed the maximum charge rate lest the battery explodes!

Radio-controlled aviation is a fascinating hobby. Learn all about its newest and fastest growing sector, electric RC helicopters at http://www.electric-rc-helicopter.com.

Article Source: http://EzineArticles.com/?expert=Tara_Soonthornnont