Electricity is everywhere.  Sometimes.  The idea came about between a few friends and myself to build a portable "power pack" so we could power our things wherever we go.

I ended up creating a contraption that housed a 12 volt battery, inverter, and battery charger inside a watertight ammo box.

Step 1: Materials

Large Electrical Components
-Power Inverter: Cobra CPI 480, 400 Watt ($26)
-12 Volt Deep Cycle Led Acid Battery: Factory Second 35Ah Sealed GEL Battery ($45)
-12 volt Battery Charger: Bass Pro Shops XPS i 5 ($72)

These parts are not too specific.  I listed what each part is, then what I used and the price I got it for.  All the things above I purchased on sale or with some discount (thrifty shopper).

Check online for an inverter, I found mine at amazon on sale at half price.

Get a Factory Second Battery.  It may sound like a bad thing, but to those of you who aren't too familiar, a factory second or 'blem' battery is one that is cosmetically damaged, but otherwise fine.  Buying a battery this way saves you at least half, which is upwards of $50.  Also, don't get a GEL battery like I did.  Get an AGM battery if you can.  GEL batteries take a special charger because they charge at a different voltage.

I lucked out with the battery charger.  I bought it in store with a 20% discount, and it charges GEL and Regular Led Acid / AGM batteries.

-Ammo Can: Find one that fits all your components. Mine is a long low 40 mm ammo can. 17" x 6.5" x 10.5"
-8 Gauge Wire: *It's important to have a heavy gauge wire to handle the large current load from the battery to inverter!*
-8 Gauge Ring Terminals
-Heavy Amperage Switch (Mine is a 50A from radioshack)
-40 Amp Marine Circuit Breaker
-1/8" Carriage Bolts, Nuts & Washers.
-1/2" Angle Iron
-1/2" Flat Aluminum Stock
-3/8" Threaded Rod
-3/8" Nuts
-1/4 20 Nuts & Bolts (Battery Terminals)

Step 2: Safety

The saying goes Safety First, to which I disagree. Safety Always.

Batteries are incredibly dangerous if you are not careful.  Ever feel how hot a AA or 9-volt battery gets when it shorts?  Imagine what a car battery full of acid could be like.  Read this http://rayvaughan.com/battery_safety.htm about exploding batteries.

Never create a short between the two terminals of a battery, or drop a tool on the terminals, or let both touch the sides of the box at the same time.

The power that the inverter outputs is incredibly dangerous.  This is the same voltage and current that comes out of the wall at your house.  The 400 Watt inverter I used outputs ~3.5 Amps.  Currents as small as 0.005 A to 0.006 A across the body can kill you.

Here are the facts about lethal electricity: http://hypertextbook.com/facts/2000/JackHsu.shtml

Now, don't let any of this information be off-putting.  Taking all the proper precautions when working with electricity and batteries (like wearing Safety Glasses for starters) can help avoid damage to the components and serious injury to yourself.

Step 3: Theory

No building yet.  Knowing is half the battle!

The Basics
Electricity - The flow of electrons.
What is important here is the electrical values.  Voltage, Current (amps), Resistance, Watts
-Volt: Electrical Pressure
-Current: Electrical flow
-Resistance: Resistance to electrical flow
-Watt: Electrical Power.  Product of Current and Voltage. (W = C*V)

This formula above is how I calculated the current of the inverter.  Yes it says it on the box, but its nice to know yourself.

Ex.  400 W = C * 115v;  C = ~3.5A

AC & DC (not the band)
AC: Alternating Current
DC: Direct Current

I could go in depth, but all you need to know is that AC is what the inverter outputs and what is in your house, and DC is what comes from batteries (don't worry, it can kill you too).

If you want to know more about electricity, google is your friend.  A link to start you out: Electricity

The Power Pack
This isn't too bad to understand.

When you are home, the battery charger takes 110v AC current (I can say that now and you should know what it means) and turns it into 12v DC to charge the battery.

When you are away from home, the inverter takes the 12v stored in the battery and turns it into 110v AC power for you to use.

Everything is then housed in a watertight ammo can so you can take it with you.

Step 4: Locks

As I was searching Instructables for things involving ammo cans I stumbled across this.  Ammunition Canister Lock Box

I took a trip to the hardware store.  I saw little 1" U bolts and thought that they would work better than a gate latch.  So I used them instead.

If you follow 646bph's instructable you should be fine.

Step 5: Construction: Battery

The battery is the largest heaviest component.  It gets mounted with a home made bracket.

The bracket is 1/2" Angle Iron welded together to form a base for the battery to rest in.  Threaded rod is welded to the outside, and eventually a piece of flat aluminum with holes drilled in it slides down on top of the threaded rod and is bolted down to clamp on the battery.

The whole bracket is JB Welded and then tack welded to the ammo can itself.

The battery itself will be dropped in last.

Step 6: Construction: Battery Charger

The battery charger goes next.

Make sure that there is space between the components and everything fits.  Both the inverter and battery charger will get hot when in use, and you want to make sure there is adequate space for ventilation.

Step 7: Construction: Inverter

Now the inverter has to be mounted.

I ran into a few problems when mounting mine.  My inverter has a "clamshell" shape that hangs over where the mounting holes are.  This prohibits me from using a socket wrench to tighten the bolts.  The other problem is that the two bolts in the corner opposite of the battery are completely in-accessible with any tool once the inverter is in place.

What I ended up doing was tightening the bolts down enough to hold it before putting the inverter in, then using loctite and fix them in place.  Then I was able to slide the inverter in and pop the other two bolts in place to secure it.  There is a picture to show this.

The other thing is that once the inverter is mounted, the wiring to it would be inaccessible.  So before mounting it attach wires to the terminals and snake them where they need to go.  Then (in the next step) it can be wired to the battery.

The last thing I did was make a ventilation hole for the inverter.  When it is running full load, it gets very hot.  And putting it in a crowded metal box is not the best for airflow.

We drilled a hole in the side of the box  and mounted a firetruck 220v watertight outlet cover over it.  The hole was placed right below the exhaust fan for the inverter.

Now when the it is running hot, the little door can be opened to allow increased airflow, and when it's not in use, it can be closed and remain watertight.

Step 8: Wiring

The wiring is pretty simple.  The positive terminal of the battery is connected to the breaker, then to the switch.  The positive terminal of the inverter is connected to the switch and the negative terminal back to the negative battery terminal.

I later added (and you can see in a few pictures) a LED power indicator, and a 12 volt automotive outlet.

They also get wired between the switch and the negative terminal of the battery.

The automotive outlet is a cheap extension cable from walmart that I cut the male end off and wired in.  One like this.

The battery charger is permanently wired to the battery as well.  It has its own marked leads that are bolted to the terminals as well.

I whipped up a wiring diagram to help illustrate as well.

Step 9: Finished!

I took this with me to the 2010 National Scout Jamboree. The week I was there had record heat and humidity. The feels like temperatures one day was 118 degrees. However I was prepared. I brought a box fan and ran it at night so we could sleep. I only got about 2 hrs on a charge with this beast of a fan, but it was so worth it. During the day I could take it to one of the buildings and charge it up. The rest of the guys used it to charge phones when we got back.

There you go.  When you turn on the main power switch, the LED power indicator will light up as well as provide power to the inverter and 12volt automotive outlet.  After that, bam.  Portable Power.
I made something similar. Very fun, great learning experience.
<p>can you post a link to yours please I'm on the planning stages for something very similar </p>
You all know that us an buy factory built versions of this don't you? booster packs and the like. just fit them with a deepcycle battery and you're rolling. there are even some with built-in inverters.
i have a booster pack that i use in my car to keep my phone charged.(security guard that sits in parking lots overnight with the engine off) it usually fully charges it several times before i bring it in my house to charge(has a plug on the back) it also is pretty light weight and doesn't take much room for when im watching netflix. and if necessary i can still jump my car.
The commercial products similar to this are not what i was looking for. One, they have small batteries, and fitting a larger battery in the existing case wasn't practical. Two, they have very small inverters. 100 or 200 watts-ish. Three, mine is built much better, and designed to handle a much higher load more safely.
I've done similar, using a hacked UPS in a ammo box, connecting larger than usual batteries to the 12V side of the UPS, and adding a 12V cooling fan to the inverter side. The key, is keeping the transistors for the inverter circuit, cooled. (and I know this, by having burned-up a 300-aH UPS. ) Most of the larger UPS's use a pair of 12V batteries, which kind of defeats the portability, so look to make sure it has a single 12V battery, and a place to connect a 12V fan to blow directly onto the transistor array.<br><br>One suggestion, adding a solar panel array to supliment the power pack during the daylight hours, and only use the battery short-term during the night. Also remember, inverters are inherently brutal on batteries. I've killed 3 full-size car batteries in under a year, subjecting them to just a simple 100-watt inverter. You can imagine what the 300-aH UPS's really do to them.
I agree,a 15 watt solar panel for around fifty bucks will keep that battery charged in the summer months,and I think you can get by without a charge control as long as you dont go over 15 watts.It is a nice little project though.
Lol. &quot;...DC is what comes from batteries (don't worry, it can kill you too)&quot;<br><br>I couldn't help but laugh.
yes, I was worried about not being killed by my 12v battery . . glad this has cleared things up :)
Where did you buy the battery?
I purchased the battery at a battery wholesaler / factory outlet. Those are probably the only places you would be able to find a factory second battery. Pick a brand of battery, and look for outlet stores on their website.
Wal-mart has some pretty decent deepcycle batteries availble. for reasonble prices too.
did you put the plugs on the outside of the box or do you have to have the lid open when you plug something in???<br>
The lid has to be open when you plug something in.<br> <br> Placing a GFCI plug on the exterior was originally in the plan, but I was worried about the heat buildup inside the box, especially when so close to the battery.&nbsp; So I ended up making a lid open during operation sort of setup.
Just install a high CFM PC case fan, thos are cheapon power useage, and chet to buy. the most exspensive one I've seen was about $5.
what if you add a small 12v computer fan i dont think .28 amps or so its too much to keep it cool? what do you think?
Yeah, 6 miliamps (mA) can kill you.
Actually 0.002 milliamps can stop a human heart, I learned that at MIT. During my first year of class.
I corrected my decimal places. I forgot a zero, and accidentally had 60mA. Thanks for pointing it out.
sorry if this pops up twice but that is highly improble the caceing wold be pritty screwd <br>A: the batery would stop working <br>B: the acid would boil and make the case burst and spit hot acid
actually 0.5 mA across the heart can kill a person.
really? ok thanks.
depends it could be 0.5 mA but a million volts that can kill you ac or dc
I read something about you using a fan, what you could do is cut mounting holes and slots in the top of the box to mount a fan, or maybe have externally mounted plugs for power and maybe an external retractable charging plug so the box almost never has to be opened.
how long do the back up power last <br>
That depend on the battery used and what its powering. Figure out how many amp hours (Ah) the battery is and how many amps are used to power your device. For example a 20 Ah battery can power a device that takes 1 amp for 20 hours. Its just division. Throwing the inverter in the mix might change that a bit, not sure. I've never used one.
You should put up an instructible on how perpetual motion/energy is impossible.
I heard that a car battery can get like 1000+ degrees
not sure that thats corect they usialy melt by then or burst and spray acid every whear
can i use a 25 amp switch
If you recall from the math section, 400 watts / 12 volts = ~33.3 amps. You can use the 25 amp switch if you want, but if you run the inverter at full load (which is easier than you think) you will melt your switch. Or worse, start a fire. So to be safe, you want at least a 40 amp (at 12v or greater) switch.
I will be useing a 200watt inverter
Then that's perfectly fine. ~16.6 amps is well under a 25 amp rating.
where do you get the 1/8 carriage bolts
Hardware store.
Do i have to have that charger thing
No, but this isn't much use without one. The whole idea of the project was to design a self contained power pack. You could use an 'external' charger, but if you forget to bring it and drain you battery, your done.
Very nice
Is it possible to plug the battery charger into the inverter while everything is turned on so that you don't have to recharge it from the grid?
Yes, it is possible, but impractical. What you are thinking of (if I'm following you correctly), is a form of perpetual energy, which is physically impossible.<br> <br> It goes like so.&nbsp; The battery powers the inverter.&nbsp; The inverter powers the battery charger. The battery charger charges the battery.&nbsp; Wash. Rinse. Repeat.<br> <br> However, things get hot.&nbsp; That energy has to come from somewhere.&nbsp; Specifically this energy comes from the inefficiencies in the inverter and charger.&nbsp; Inside the manual itself it has under the specs: &quot;Efficiency (full load, 12V).. &gt; 83%&quot;.<br> <br> That means that it looses 17% of its energy in the conversion between 12v and 120v alone.<br> <br> So to answer your question in short:&nbsp; Yes it is possible to plug it in, but it still has to be charged via other means (grid, vehicle, solar, renewable... etc.)<br>
Thanks for the answer. I am trying to build this for camping where thier is no electricity for miles and was wondering if i could plug it straight into the inverter or if i could use a second battery and a more powerful and efficient inverter so that while one battery is powering the inverter the other is charging. Wouldd that work instead of having just one battery?
You only have so much power no matter how you look at it. There is no way to pull energy out of nowhere. Once it is used powering something, it's gone.<br> <br> Your best bet, depending on how long you want to run, and how much power you need to draw, is to get many large batteries.&nbsp; The more batteries you have the larger your reserve is, and the longer you will last.<br>
thats a clean looking setup there.
Why thank you. That was my goal; something that I could load up, be rugged, and completely self contained.
Youve got a pretty basic idea here.. Is there anyway to make a hand crank for it instead of having to charge it on the grid power? If this hand crank was added this could be something that you could manufacture i would instanty buy one <br> <br>i built it it works great i just dont like the idea of having to &quot;Charge&quot; it <br> <br>Thanks anyways <br> <br>-CircuitBoy
A hand crank would work, it would just be impractical.<br> <br> Using this <a href="http://www.csgnetwork.com/batterychgcalc.html">charge calculator</a>, a 35000mAh battery charging at the 6000mA that my charger outputs should take 7 hrs (at 20% ~typical energy loss).<br> <br> Using a <a href="http://www.windstreampower.com/Human_Power_Generator.php">human power generator</a> and cranking by hand only produces 35watts ~typical.&nbsp; Thats ~3000mA.&nbsp; Running at that rate, it would take 14hrs to fully charge the battery.<br> <br> A hand crank is better suited for smaller scale power usage.<br> <br> <br> Also, you said that you built one yourself.&nbsp; I would love to see pictures of it.<br>
I will Attempt To i first have to buy a camera as my soildering iron fell into my lens whn i was testing infered LEDs
Well, I'm nearly done making mine. I had to put it inside of a small cooler, but instead of a wall charger, I used a solar panel and charge controller. All the electronics work fine and I'm charging it up now. Pics to follow once I put all the finishing touches on it.
The lid has to be open when you plug something in.<br><br>Placing a GFCI plug on the exterior was originally in the plan, but I was worried about the heat buildup inside the box, especially when so close to the battery.&nbsp; So I ended up making a lid open during operation sort of setup.
that makes sense i think if i am going to do this i will put in a bigger ammo box.<br>what size was your box?<br>

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Bio: Proud Eagle Scout & Engineer In Training.
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