2700 mAh worth of Li-Po batteries inside my JG AUG (big pics)
 

As anyone who owns an AUG knows, the battery compartment is TINY. With standard cells, there's room for a 1500 mAh 9.6V, but that's about it.
I used to have a large 3300 mAh 8.4V NiMh battery strapped to the side of the gun, but I hated that. It was really heavy.
So the obvious solution (and the one potentially involving the most fire) was to go the Li-Po route!

The batteries I used are intended for an RC helicopter. I got them here:
http://www.dealextreme.com/details.dx/sku.7621
Using the "bulkrate" coupon brought the price down under $7 each.

I wired them in parallel. Since each is 900 mAh, this means I have a total of 2700 mAh. Mind you, it's only 7.4 volts but these things are powerful. ROF was much higher than with the stock 8.4V mini. It was on par with the 8.4V large battery, or a 9.6V mini, both of which I've tested in my gun.

Here's a pic of all 3 after I soldered on the deans connectors:
http://img.villagephotos.com/p/2007-7/1267121/all.jpg

This pic blows my cover as an american :D
http://img.villagephotos.com/p/2007-7/1267121/one.jpg

It fits! I made a harness to split my AUG's single deans connector into three. This way I can still use a single battery if I want.
http://img.villagephotos.com/p/2007-7/1267121/fit.jpg

The rubber buttplate goes on fine. No bulges!
http://img.villagephotos.com/p/2007-7/1267121/stock.jpg

I'm really happy with how this turned out. I was keeping my fingers crossed that the ROF would be acceptable, and it definitely is. Plus, you can't argue with 2700 mAh INSIDE an AUG.

Any questions? :cool:

Ahhhh!
I've been waiting for such a solution for some time.
You, sir, definitely deserve congratulations :)
It's also nice to know the ROF is correct.
good job! :)


ps: the whole thing would even be smaller with banana plugs.awesome.

Thanks!
But what do you mean by banana plugs? The only banana plugs I know of are bigger than deans connectors...

http://www.onlybatteries.com/

there I got a battery mounted with gold plated banana plugs that are really small.

What do you have in mind for a low battery cutoff circuit?

Lipos don't like being discharged too much.

I guess I figured the gun wouldn't turn over once it got down to 6V, and I'd just stop firing when that happened :p
Is this a bad idea? I could always put together a simple circuit I suppose, at least until my uber-custom microcontroller-based mosfet project is realized :D

Aren't you worried about....oh I don't know.....fire or exploding?

Also, relating to this, was this just a slip of the mouth, or intentional?

Yep. I've been opening it up after every time I fire it, making sure the batteries aren't warm or swelled. I'll be less nervous after they've proven themselves in a few skirmishes. :p
The parallel configuration does increase the risk slightly. I figured I could keep the potential for explosion minimal by using the same brand/size cells. Plus I check the voltages with a multimeter before I plug them in.
Li-Po is the future! :cool:

grab these http://projectwolfdragon.com/Products/LiPO-PCB.htm, and why not also grab one of these http://extreme-fire.com/SW-COMPUTER.html.
after that, you'll be peachy

I was planning on eventually building my own custom sw-computer (I'm studying electrical engineering and it'd be a cool project). I hate the AUG's trigger feel, and if I added some wires and some programming to the SW-computer, I could remove the huge clunky trigger linkage that runs through the gun. Maybe this summer when I have some time...
...Anyway, I think I'll take my chances for now. The first couple of battery cycles I'll keep a close eye on the voltage, to find out how much warning I get before it's down to 3.0V per cell. If I discharge one too much, it's a $7 mistake :p

Not a good idea
 

Hey get a cheap led or other warning device for those lipos. You have two issues fire a very real danger and tanking the cells. I fly rc helis in my spare time,(when not playing airsoft). A more than few people have had on board fires or killed the batteries. A small warning LED under your sights would save you a world of grief.

That's a good idea. I just may make a circuit to do that, and post more pics.

You want some thing like this
 

Any hobby shop that carries LIpos and Rc Helis should have these but if not this is a good choice, I use it on all my heli's.


http://helihobby.com/html/lithium_batteries.html


Lightning Power Onboard Battery Monito




Stop flying while guessing when will your main pack run out. With this inexpensively little gadget you can fly with confidence. Simply hover in front of you and read out the bright LEDs. If one of the LEDs turn RED you know its time to land, its that simple. Designed for one to three cell Lithium batteries and plugs directly to the balancing plug.



9.99


PART#LP-E0201

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- Instructions:
- Match up the positive to positive and negative to negative terminals. In the event that positive and negative wires are mixed up, the Lightning Power Onboard Battery Monitor will not light up. No damage to the unit or battery will occur. just reverse the connection.
- Each cell is at or above 3.3 volts when the corresponding light is green ( ex. 3S Lithium Polymer pack @ 10 volts equals three solid green lights on the monitor)
- Whenever any cell drops below 3.3 volts, a red light will turn on. Tthe battery monitor will work only if the battery is under load ( ex. hovering the helicopter).

- The kit includes the following:
- Battery monitor
- Two 4.5 inch wire extensions (Thunder Power/ Flight Power and Lighting Power compatible)
- Double sided foam tape

Flaming RC helicopters? Sounds like something I'd make.

Unfortunately since I have 3 packs, I'd have to get 3 of those monitors, or just make one that alerts me when the overall voltage goes below 6.6 or so. Which is probably what I'll do. Like I said, one dead pack is not an expensive mistake, plus my airsoft gun doesn't need to hover.

lol @ the logo for your LiPo batteries, "Mystery" .. and its in flames hehe

A bit disconcerting, to say the least.

im using 11.1v Li-Po batteries now and i love them.
im running a PGC M130 spring (430FPS) with insane ROF (had to reduce motor speed by 40% to prevent stripping thanks to the SW-computer from ExtremeFire). the batteries hardly get warm, they stay cooler then the NiCads and NiMH i used befor. that and they last longer then nicads and nimh of the same mAh rating. my 1200mAh Li-Po out lasts my 1650mAh nimh battery easy.
as long as you dont do anything "stupid" with the Li-Po batteries, they should be as safe as any other battery.

Guys you DO need the cutoff circuit to prevent a fire. The batteries can heat up way faster than NiCAD or NiMH and heat isn't a good pre-fire warning. Also if they do catch fire, the smoke that comes off of them is really nasty toxic stuff that you really don't want to be handling without proper training and equipment, not to mention the possibility of burns.

Buy the protection circuit.

ok
and what would a mosfet do ?

Mosfet isn't a LiPo protection circuit. The protection circuit is a very specific circuit. I would not run without one.

hum...where would we put that on a AUG ? inside?
pinching holes in the buttplate?

...a transparent buttplate would be good for that :)

You could also try something like this:

http://www.hobbycity.com/hobbycity/s...idProduct=2160

It's not that big, and makes a noise when your cells drop below 3v.

I built a modified one of these:
http://www.reuk.co.uk/12-Volt-Batter...ator-LM741.htm
And stuffed it in there. I stuck the LED out of the right side sling mount hole. It lights up when the battery's voltage goes below 7.0. It also flashes every time I pull the trigger. Makes my gun look high tech :p

I just ordered a couple of these from RSOV.com; we'll see how they work out. They plug right in to the JST port on the battery:

http://www.rsov.com/product/105_133/...rm-buzzer.html

http://www.rsov.com/images/bat_0045.jpg

http://www.rsov.com/images/bat_0045_1.jpg

Li-Polymer battery cells voltage monitor and alarm buzzer for 3-cells Polymer battery equipped with reverse-polarity protection.

- The green LED indicate the battery cell condition is good (3.8-4.2v).
- The red LED indicate the battery cell need to be charged to maintain the performance (3.5-3.8v).
- The red LED will turn on and alarm buzzer will sound when the battery cell is either under or over voltage ( <3.5v or >4.2v ).

The PCB is protected by heat-shrink insulation sleeve so you can stick the indicator to the Polymer battery on your AEG or RC plane for easy battery monitoring.