A Portable Power Box for Photographers

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A Portable Power Box for Photographersby Divet on July 6, 2008

Table of Contents

A Portable Power Box for Photographers ............................................................................................

Intro: A Portable Power Box for Photographers ....................................................................................

Step 1: Angle Brackets ......................................................................................................

Step 2: The Inverter ........................................................................................................

Step 3: Spacing ............................................................................................................

Step 4: Wiring .............................................................................................................

Step 5: Breaker ............................................................................................................

Step 6: Ground Fault Circuit Interrupter ..........................................................................................

Step 7: Ground ............................................................................................................

Step 8: Finish .............................................................................................................

Related Instructables ........................................................................................................

Comments ................................................................................................................
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Intro: A Portable Power Box for PhotographersMany photographers have built Vagabond style portable power systems to use with their strobes. This is an attempt to incorporate several design ideas and safetyfeatures. The power box can also be used with laptops or other delicate electronic equipment.

Materials:

Metal tool box (18'x8'x9' or larger)300 watt Samlex pure sine wave inverter (Frys.com $130)Scooter/wheelchair battery 26AH-35AH ($40-$100)40 amp Square D Breaker QO (single pole AC/DC breaker $14 electrical supply store)8 AWG Braided Electrical Cable (SOOW 8GA $12)Bolts and lock washers(2) Brass washers(2) 2 1/2' and 3' angle brackets

Ground Fault Circuit Interrupter (GFCI) and Box Housing ($16+$5 Home Depot)Old scrap extension cord with plugLarge nail or spikeHose clampZip tiesFlat piece of hard plasticCopper ground wire stripped from an electr ical cableBattery clamps

SAFETY: Disconnect the battery when working on the circuit. Wear gloves when handling the battery.

Image Notes

1. Pure Sine Wave Inverter2. Battery3. Ground Spike4. Breaker5. GFCI

Step 1:Angle BracketsUse a metal tool box to house the power supply. It will serve as the common ground for all the components. The box should be tall enough so that when closed, the liddoesn't touch the battery terminals. Place the battery as close to the centre as possible for even weight distribution. Do not use a car battery for this project as it quicklwill become damaged from being repeatedly discharged.

Mark and drill holes for the angle brackets. Remove the paint from under the left 3" bracket. This bracket will attach to the ground spike. 2 1/2 " brackets were used onone side because the box was not wide enough for 3 inch.

Mark and drill holes for the inverter and the inverter ground bolt. Remove any paint from around the holes so there is a good electrical contact.


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Image Notes1. Inverter Ground Bolt & Washer2. Inverter Holes3. Inverter Holes4. The Ground Spike will be bolted here.

Step 2:The InverterIf you don't use a pure sine wave inverter, you will risk damaging your strobes. Samlex pure sine wave inverters have a good reputation and I would strongly recomme

them over another cheaper brand. Some modified sine wave inverters are deliberately mislabelled and sold as pure sine wave inverters.Attach the inverter with bolts and lock washers. Whatever surface you mount the inverter on, it must be horizontal or the internal fan will not work properly. Use thestripped electrical grounding wire to attach the inverter ground connector to the tool box ground bolt. Ideally the grounding wire should be 6 gauge, but it's difficult to wwith anything that large in a small space.

The European division of Samlex also sells 230Vac pure sine wave inverters for those whose strobes are not 120Vac.

I've heard rumours that Samlex has significantly changed the design of their inverters since I built the power box. I have not tested these new inverters, but it would binteresting to know how well they work.

Image Notes1. Tool Box Ground Bolt2. Inverter Ground Connector (hidden)


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Step 3:SpacingPlace the battery in the box to check spacing. If I did it again, I would mount the inverter facing the other direction on the left side of the box, so that the power switch ithe top and easily accessible.

Image Notes1. The power switch is below the electrical socket and is hard to get to whencables are plugged in.

Image Notes1. There is no contact between the inverter and battery.

Step 4:WiringThe Samlex manual indicates that the inverter needs a 40 amp fuse. It's a common electrical practice for a 40 amp circuit to use 8 gauge cable. With a large cable, it iseasier for the inverter to draw the amps needed to run the strobes. Standard household 12 gauge wire is too small and will cause the inverter to beep and switch to amodified sine wave.

Use braided 8 AWG wire instead of stranded. It is much more flexible and will put less force on all the connections. SOOW 8GA cable has several braided wires insideand is relatively inexpensive.

Tin the ends of the cables and solder/torch on the battery connectors. Use full sized battery connectors. Smaller sized connectors can limit the maximum load by over400 watts. I was unable to find the appropriate inverter connectors, so I tinned and shaped the wire with pliers so they would fit inside the inverter power sockets.

If the inverter will not power over a 1000 watts of strobes without beeping, unsolder the battery clamps and try directly attaching the wires to the battery terminals withbolts and washers. Use two washers on each terminal to help prevent the bolt f rom being pulled through. Cutting the ends off a 2 1/2" corner brace makes very stronsquare washers. In the future I might try using the wire from a pair of old jumper cables to see if there are any amps to be gained by having a larger conductor.

Image Notes1. SOOW 8 Gauge Cable2. Each wire is 8 gauge.

Image Notes1. Tinned Wire


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Image Notes1. Corner Brace Washers2. Corner Brace connector torched on.

Step 5:BreakerThe 40 amp Square D QO breaker is designed for use in DC circuits. The breaker will help to protect the inverter and is easier to use than a 40 amp fuse.

The circuit for the power box is:battery positive --) breaker--) inverter positivebattery negative --) inverter negative

Drill bolt holes and zip tie holes in the flat piece of plastic. Solder on the positive battery cable to the breaker with a 100w soldering iron. Attach the breaker output cabthe inverter. Bolt and zip tie the breaker to the side of the box.

Image Notes1. From the positive battery terminal2. To Inverter's positive connector


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3. Bolt Holes4. Zip Tie Hole

Step 6:Ground Fault Circuit InterrupterA GFCI is designed to instantly cut power to the outlet if there is a short. When shooting outside you will get rained on, so a GFCI is essential.

Assemble the GFCI in a housing according to the instructions. Attach the end of an old extension cord to the GFCI and test it to see if the reset button is working prope

Make sure there is enough space in the tool box to easily plug cords into to the GFCI after it is bolted into place. Remove paint around bolt holes for a good ground. Pthe GFCI into the inverter.

Step 7:GroundA ground spike may not be necessary/usable under all circumstances, but it adds an additional layer of protection. In the event of a short, it will hopefully channel thecurrent harmlessly into the earth.

Tin the ends of a 8 gauge cable. Solder one end to a brass washer and hose clamp the other to a large nail or spike. Electrical tape the hose clamp connection and bothe washer to the left 3" angle bracket.

Image Notes1. Hose Clamp

Step 8:FinishPortable Power Box Setup

1. Push ground spike into the earth ( If possible)2. Attach negative cable to battery3. Turn on breaker4. Attach positive cable to battery5. Turn on inverter6. Turn on strobes

Always connect the positive terminal last, so that any arching occurs on the cable that is protected by the breaker. When the positive cable is disconnected, do not alloto touch the metal box. Turn the breaker off first. Some people have reported that the capacitors in the inverter can still hold a charge and can feed voltage back throuthe battery cables.

Turn off all the strobes before turning off the inverter. Do not store the power box with the battery connected. The portable power box with a 33AH battery will run two


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watt strobes (not at maximum settings) for over 210 flashes. I have not yet drained the battery shooting under normal conditions.

Image Notes1. Pure Sine Wave Inverter2. Battery3. Ground Spike4. Breaker5. GFCI

Image Notes

1. Musician photo shoot in an abandoned building using the portable power box.

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Comments

50 comments Add Comment view all 58 commen

thepaul1993 says: Jul 19, 2010. 5:47 AM REPVery nice. I guess if you wanted to you could add a charge controller and a solar panel.

ElectricMan1 says: Feb 19, 2010. 5:52 PM REPDude, thats way overkill on the wire, 300watts/ 12volts= 25 amps DC.25 amps for less than a foot= 12 guage flexable wire is fine.

I use #10 on my 400 watt inverter system.

Divet says: Mar 31, 2010. 8:10 PM REPI tested with scraps of 12, 10 and 8 gauge wire when building the box. 8 gauge allows more watts.

darkride says: Dec 22, 2008. 3:14 AM REPUm, a GFCI doesn't protect against a short, it protects you from being electrocuted by touching the hot wire while having a path to ground, such as when inwet environment. Since this project is not using commercial power (which has a good ground path), I doubt it is of much use, just added cost, leave it off.Lose the ground spike (which is not long enough to be of any use anyway.) and there is no path to ground. With no connection to earth ground the only wayou could electrocute yourself would be to touch both AC wires at the same t ime. By the way, it doesn't matter which battery lead you attach fi rst, just makesure the breaker is off.

Divet says: Dec 22, 2008. 10:25 AM REP

Using a power box in wet environment with a sync cord can result in a photographer receiving shocks through the camera. Installing a GFCI and aground spike is an attempt to minimize the possibility of damage to either equipment or personnel.

ElectricMan1 says: Feb 19, 2010. 5:46 PM REPGFCI- GROUNDfault circuit interrupter.The inverter is poorly grounded if at all, the best thing to do is not get electrocuted.

vodo says: Mar 13, 2009. 10:09 AM REPfield bought a battery at radioshack. it is an alarm battery, here air the specks: charging voltage: 14.4-15.0v 13.5-13.8v. application:normal chargestandby/trickle max charging current: 1.5a 1.5a. can I use it to build it? oh,an its 12v.

Divet says: Mar 21, 2009. 4:33 AM REPSee if there is an AH marking. I think most 12 volt batteries at Radio Shack are under 8 AH. 10AH would be the minimum I would try.

ReCreate says: Apr 22, 2009. 8:18 PM REPI used a 700MAH battery for an inverter and it ran a 60 watt fluorescent light for a while,So its about 1 amp hour,if the Light consumed 100miliamphours(i know it does not though)it would last for 7 hours,if i t consumed 700miliamp hours it would last,1 hour

ElectricMan1 says: Feb 19, 2010. 5:41 PM REPIn a perfect world, batteries don't drain 100%.I learned that the hard way!

alex-sharetskiy says: Jul 27, 2008. 12:53 PM REPThe battery is a bit heavy? anyone got links to cheap Li-Poly batteries?

ReCreate says: Apr 22, 2009. 8:24 PM REPHO NO,LITHIUM-ION COSTS THAUSANDs Really They are very expensive,and they are dangerous to charge too! just overcharging them by ahundredth of a volt and you get KABOOM

alex-sharetskiy says: Apr 23, 2009. 6:41 AM REPif you over charge by 1/100 of a volt, you only slightly damage the battery

ReCreate says: Apr 23, 2009. 10:31 AM REPHa yeah,its a 1/10 of a volt not a 1/100
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alex-sharetskiy says: Apr 23, 2009. 2:14 PM REP1/100 of a volt actually decreases the cycle life by just a tiny bit if a battery is charged to 4.20v it has less capcity, but lasts longer then abattery charged to 4.235V

ReCreate says: Apr 23, 2009. 3:12 PM REPthe battery is rated 3.7 Volts,if it is at 4.20 that means that it is overcharged,big time

alex-sharetskiy says: Apr 23, 2009. 5:53 PM REPand that....................... is where you're wrong 3.7V is just nominal cell voltage When fully charged, the battery is at 4.15-4.25 Voltssame thing for nicad, nimh, and Lead-acid batteries, they are said to be a certain voltage, but they need to be charged more then th

ReCreate says: Apr 23, 2009. 7:41 PM REPI don't get it,so batteries are not really what they say? But much higher?

alex-sharetskiy says: Apr 24, 2009. 6:43 AM REPnot 'much' higher and only rechargeables regular batteries have the voltage that is printed on them

ReCreate says: Apr 24, 2009. 10:29 AM REPSO lithium ion batteries to et overcha red,to 4.20 volts,when the are rated 3.6 volts,so what are their real volta e? 4?

alex-sharetskiy says: Apr 24, 2009. 2:05 PM REPthere is no 'real' voltage the voltage changes when fully or partially charged

ReCreate says: Apr 24, 2009. 4:15 PM REPI guess so...So what would be an over charged lithium ion?

alex-sharetskiy says: Apr 24, 2009. 6:14 PM REPAn overchar ed i-ion would be 4.2+ V a char ed li-ion would be 4.2V a full drained li-ion would be 3.6V

ReCreate says: Apr 24, 2009. 8:13 PM REPI guess you learn something new every day!

alex-sharetskiy says: Apr 24, 2009. 8:31 PM REPover the course of two days

ReCreate says: Apr 25, 2009. 6:21 PM REPI meant that that ou said that da ,i thou ht that it was to 3.7.not 4

ElectricMan1 says: Feb 19, 2010. 5:39 PM REPHAok they should come up with another name for Lithium Polys: BOMBS

dooj says: Sep 8, 2009. 11:19 AM REPand plese give me i link

Divet says: Sep 8, 2009. 4:55 PM REPSearch on Ebay for a wheelchair/scooter battery.

http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=wheelchair+battery&_sacat=See-All-Categories
http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=wheelchair+battery&_sacat=See-All-Categorieshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/Divet/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/Divet/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/dooj/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/dooj/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ElectricMan1/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ElectricMan1/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/ReCreate/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/id/A-Portable-Power-Box-for-Photographers/?utm_source=pdf&utm_campaign=comments#DISCUSShttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=commentshttp://www.instructables.com/member/alex-sharetskiy/?utm_source=pdf&utm_campaign=comments


10/11


dooj says: Sep 8, 2009. 11:18 AM REPwhere did you get the battery

sbgstudios says: May 3, 2009. 3:40 PM REPI understand why you left everything inside. There would have to be alot of fab work to get that single gang box supported correctly from the inside. Samewith the the breaker... I like fab work, so m version will rob have both accessible from the outside. Love this instructable thou h, well done.

sbgstudios says: May 3, 2009. 3:29 PM REPJust an all around good idea. If your a big dude like me... get two batteries (maybe a little smaller), and run them in parallel. Or is it series? I can neverremember (thanks high school electronics class).

brian3140 says: May 2, 2009. 4:41 PM REPThe concept is good, but electrical theory in the comments is very confused. definitely put the GFCI on the outside of the box and don't worry about rain orwater. it'd never be ideal to do it on purpose, but the GFCI will protect you even if you sprayed it with a hose. In rain there is a high likely hood that it willnever even trip the GFI on the outlet, but if it does... oh well. that is what it is designed for. And no rain cover is necessary. People trying to make the systelighter should just stick with the heavy battery, but a smaller cheaper inverter could be used. I bought a 400 watt inverter at Wallmart a few years ago for $4and never had any trouble.

ReCreate says: Apr 24, 2009. 4:17 PM REPThe Inverter should provide you 300 WATTS for 1 hour...I think

ReCreate says: Apr 25, 2009. 6:20 PM REPSo according to my calculations,IT should last... few days at 30 or so watts

josh.wingo says: Apr 24, 2009. 11:29 AM REPyou should cut a hole on the side for the gfci to face outwards. so you do not need to run power out of the box, the box can stay sealed. when facing the gfout, get a weatherproof box cover, it will keep water from getting in it and you can still safely use it in the rain.

animes25 says: Jul 29, 2008. 5:06 PM REPand the million dollar question is: How do I recharge the battery when is worn out?

Divet says: Jul 30, 2008. 5:10 AM REPUse an intelligent car battery charger.

ReCreate says: Apr 22, 2009. 8:21 PM REPor any charger,or any supply of 12-15v

ReCreate says: Apr 22, 2009. 8:15 PM REPwhat are the specs of the battery?(other than voltage of course its 12v) Lets see...50 ma is lethal,the battery being 12v will let only 0.20(about) ma throughour skin,therfor.0.20 out of the lethal 50.0 ma is oin throu h ou, our safe touchin the leads, ust as lon as ou don't have salt water on our hands

mbainrot says: Feb 11, 2009. 9:36 PM REPOne thing i noticed is that you have set the inverter up in a way which puts it in an enclosed space, if your not careful you can overheat the inverter.

With the AH question, in theory you can get away with as low as 7AH, (which is what i use to power computers etc), the important calculation you need tomake is how long you get, MINUS the safety cut off (most inverters will shutdown when the battery voltage gets too low), also you need to compensate forthe efficiency of your inverter, batteries, etc.

For example :)To calculate approximately how long a 7AH battery will last on a 300 watt load (my inverter @ 100%), you would do the following :)

1) Convert the watts into "dc amps", this is down by dividing the wattage by the operating voltage of the inverter (so in this example its 300 divided by 12,which gives you 25A)2) Then you add the inefficiency amount (so if its 95% eff, the inefficiency is 5%) to the amperage (so in this example, 25*1.05, which gives you 26.25A),then you add the approximate efficiency of your battery (Sealed lead acids trend around 90%, so in this example, 26.25*1.10, gives you 28.875A)

3) With the final figure from the last calculation (in this example its 28.875A). you divide the amp hour capacity of your battery (or total capacity of yourbattery bank) by the amp figure (e.g. 7AH / 28.875A = 0.24 hrs or approx 15 minutes)

Please note that the voltage cut off will usually prevent the battery from getting lower than about 10.5volts, which leaves you with piss all power from thebattery.

Other notes are with measuring equipment to determine your needs, please note that inductive loads sometimes cannot be measured (no idea why)

Ho efull m 5 cents is of use to eo le :)
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11/11

http://www instructables com/id/A Portable Power Box for Photographers/

brandegor says: Jan 16, 2009. 10:49 AM REPWould this be safe to run video cameras as well?

Divet says: Jan 19, 2009. 5:52 PM REPYes. Power supplies for video cameras are usually under 20 watts.

lgcalex says: Sep 6, 2008. 9:11 PM REPthis is great! I didnt see how much shooting you can do off of one of these. How many watts are you strobes/ number of times you can fire them? I wil l moslikely be building one of these in the near future. The strobist method doesn't allways work if you need more l ight

Divet says: Sep 10, 2008. 6:35 PM REPThe portable power box with a 33AH battery will run two 600 watt strobes (not at maximum settings and with some use of the modeling light) for over 2flashes.

mattccc says: Aug 22, 2008. 6:34 PM REPcan i use a 4.5 ah battery instead

Divet says: Aug 26, 2008. 9:55 AM REPA 20AH battery is the lowest I've seen used for photography purposes. Some people have said that 15AH is the minimum.

Dipankar says: Aug 2, 2008. 4:26 PM REPYour Photography is of excellent quality.

animes25 says: Jul 30, 2008. 7:09 PM REPI will make this one but, I will use a laptop bag instead the metal box, hope never to fall in a river or swimming pool :D

animes25 says: Jul 29, 2008. 5:00 PM REPI have a 300 watt ure sine wave inverter, and it haves a fuse, I think thats enou h

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A Portable Power Box for Photographers