Instructables
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.
 
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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.


Hardware
-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)
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Gelfling63 years ago
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.

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.
Wally_Z3 years ago
Lol. "...DC is what comes from batteries (don't worry, it can kill you too)"

I couldn't help but laugh.
hbell Wally_Z3 years ago
yes, I was worried about not being killed by my 12v battery . . glad this has cleared things up :)
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.
zcshiner (author)  alien2000496553 years ago
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.
EvilMarker3 years ago
Where did you buy the battery?
zcshiner (author)  EvilMarker3 years ago
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???
zcshiner (author)  theatre_tech_guru4 years ago
The lid has to be open when you plug something in.

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.  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?
account3r24 years ago
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.
zcshiner (author)  account3r24 years ago
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
A: the batery would stop working
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
Wally_Z3 years ago
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.
ilongsworth3 years ago
how long do the back up power last
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.
tbt10f3 years ago
You should put up an instructible on how perpetual motion/energy is impossible.
account3r24 years ago
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
EvilMarker3 years ago
can i use a 25 amp switch
zcshiner (author)  EvilMarker3 years ago
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
zcshiner (author)  EvilMarker3 years ago
Then that's perfectly fine. ~16.6 amps is well under a 25 amp rating.
EvilMarker3 years ago
where do you get the 1/8 carriage bolts
zcshiner (author)  EvilMarker3 years ago
Hardware store.
EvilMarker3 years ago
Do i have to have that charger thing
zcshiner (author)  EvilMarker3 years ago
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?
zcshiner (author)  bmrodgers33654 years ago
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.

It goes like so.  The battery powers the inverter.  The inverter powers the battery charger. The battery charger charges the battery.  Wash. Rinse. Repeat.

However, things get hot.  That energy has to come from somewhere.  Specifically this energy comes from the inefficiencies in the inverter and charger.  Inside the manual itself it has under the specs: "Efficiency (full load, 12V).. > 83%".

That means that it looses 17% of its energy in the conversion between 12v and 120v alone.

So to answer your question in short:  Yes it is possible to plug it in, but it still has to be charged via other means (grid, vehicle, solar, renewable... etc.)
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?
zcshiner (author)  bmrodgers33654 years ago
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.

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.  The more batteries you have the larger your reserve is, and the longer you will last.
thats a clean looking setup there.
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