AEG LiPo battery fire - what's next

[mantakree]

Hey. So I had fun last week. Tested my M4 AEG, modded by some dude, it worked fine until wednesday.
So here's how it happens: I put on my LiPo 7.4 battery, fire a few empty shots, realize my trigger safety is shit and i fire one shot when in safe. don't think much of it, bring gun down to basement range.
before i can shoot, i see some smoke coming out of my battery holder (fake PEQ box, it wasnt closed completely since i was inside).
Before I can react, LOTS of smoke starts coming out.
Luckily, I'm prepared for most eventualities and have a pair of wire cutters nearby. I slice the wires (cutting also the deans which had melted from the heat), start my industrial fan (big into airbrushing) and leave the room, grab extinctor but it wasn't needed.

So blablabla, i throw out my ruined PEQ with battery still inside outside in the snow once the smoke literally clears.

Now, it might have been a punctured battery, over discharged, i don't know. What i want to know, is how do i make sure the gun wasn't harmed, is there anything I should check before getting new connectors and plugging another battery in?
Could it have been a poor contact due to my safety failing to be safe?

[Bakasaur]

1) are there shorts/nicks in the wiring anywhere on the harness?
2) Do you and a mosfet? If yes, are you sure the wiring is correct?
3) Wires solder points are heatshrinked?

[DeWee]

Did you install the deans connectors yourself?

Connector may have just short circuited...

[RainyEyes]

Do not plug in another battery.

Inspect the trigger contacts and the inside of the gearbox for any kind of defects. First and foremost, fix the faulty trigger safety. Replace it, etc.

Second, inspect the motor. Does it spin, short, cause sparks, etc.

Third, wiring. Look at the soldering job, if it touches anything it shouldn't. If there's a fuse, inspect that as well.

Do not connect a battery in anything until you are 100% satisfied that everything is in working order. In the off chance that the lipo bursted into flames by fluke, you're still better off confirming that it wasn't the wiring that caused it. The last thing you want is a repeated incident.

Lastly, what modifications were made, and what brand AEG is the m4? You could potentially hold the previous technician accountable for any faulty work that was done, if any.

[mantakree]

thanks for all the answer. to keep it brief:

- not originally my gun, bought it on a facebook trade group. used to work great until everything went to shit in one go
- not really good as disasembling m4's. last time i tried i messed up and somehow lost pieces, broke everything (another m4, unrelated)
- there didn't seem to be any wrong contacts with the wires but i might have missed it somehow

guess i'll have to find a gun doc and have him to a checkup then. anyone recommended in the general montreal area?

[pestobanana]

Get a multimeter, test your gun and make sure it was shorted. It most likely is shorted, so take your gun apart and fix that. "Modded by some dude" sounds like the culprit to me.

[lurkingknight]

if mosfet, check all wiring.

if no mosfet, check trigger contacts and wiring. I'm thinking you caused some sort of arc and jam. The way the safetys work in airsoft guns is a phsyical block of the gun trigger, not of the trigger shuttle. So if you defeat the block by whatever means, it's possible the trigger block can be moved into the contacts to fire the gun. having a saftey does nothing in this regard. The only true safety in an AS would be a kill switch at the battery.

So I'm thinking something went wrong inside your gearbox. If the gun was not shooting and it began to smoke, you could have had a mechanical jam that prevented the motor from turning but would still attempt to turn, creating a draw, this can potentially overdraw the battery if it's a shitty quality lipo on a big neo magnet motor. Even a shitty stock torque motor can overdraw a decent lipo.

This happened to me on a CA torque motor. The piston jammed on a cycle, on the very next sector it engaged the piston in the wrong spot and jammed the piston. At the same time the motor drew more power then there was a big arc at the contacts that melted the housing that fused the 2 contacts together, so even without the trigger block pulled forward, it closed the circuit and drew the max amps the motor could draw, the result was my 30C 7.4 1800mah pack started swelling. Luckily it was on my test bench and I was able to pull it apart.

But this is the exact reason people should have mosfets put in. The contacts will never arc and fuse together like that.

I'm thinking it's quite possible this happened to your gun.

edit

I am also wary of 'modified by some guy'
Find a good gun tech. If you were in ottawa I'd tell you to bring it to me, but unless you're willing to drive it into ottawa, you'll have to find someone more local. lol.