Batteries keep blowing up!

[FNinjaP90]

I'm was making this pack for my Airsoft gun consisting of 8 Sanyo KR-1700AU 1700mah NICD A cells that I got from batterystation. After I finished the pack, I put it on my gun. The two terminals accidentally touched the aluminum mechbox for a few seconds and one of the middle cells started to heat and fizz up and got destroyed.

I thought all the other cells were fine so I ordered another one. After I completed the pack again, I discharged and charged it. After I ran the pack on the motor, another cell(not the cell I just ordred,) got destroyed. This is sooo annoying! How sensitive are these cells to short circuiting? I have been charging them at 4A, so I don't think that is tooo much.

I bought the first 8 cells at Batterystation for $23 to save money from the $48 that a premade airsoft pack would cost. Add another $5 for the individually shipped cell and we are only $20 away. I'm just wondering, if this has happened twice so far, are any of the other cells damaged? If so, I would have to either order 8 more cells or just get a $48 premade pack. I can either save money and risk blowing more cells or just spending a little more and getting a premade pack. This is really really annoying...

 

[6pOriginal]

Is it possible there's a bad cell somewhere? /ubbthreads/images/graemlins/thinking.gif

I remember batterystation also offer ready to use custom packed battery packs at pretty good price. I have been thinking about using this RC Li-poly battery on my CAR-15, yes, the voltage is a little off (either 7.4 or 11.1) but it's small and light and I have been using a 7.2v NiCd pack on my CAR-15 for many times, it runs just as well.

 

[FNinjaP90]

The first 8 I ordered were overstock cells that were like $1.50 each. Batterystation guidelines say that overstock cells can't be made into packs. I would then have to order $3 normal cells.

Kevin said that after I ordered them some dude ordered the rest of them, so when I was ready to order the cell that replaced the cell that blew up, they were already out of stock. I had to buy that cell individually at $3.5, plus shipping, which adds up to like $6 or $7.

I'm pushing a PDI190% with normal gears, so I don't think the 8.4V of the existing cells would work.

 

[unnerv]

It could be a combination of things, but those cells are not meant to be charged at more than 2.6 amp. More than that and you really risk overheating them. Shorting is really bad too if it happened for more than a few seconds again, because of the heat. If you wanna take a look at the spec sheet here is a link to it on Sanyo's Web Page .

If I were you, I would disassemble the pack and charge each cell individually and then discharge individually with a moderate load like 2 amps and see if any of the cells seem way out of line. Discard any cell that is out of the ordinary and rebuild the pack. I would use the newest cell as a baseline if possible. Also when soldering, try to make the joint as quickly as possible, otherwise the heat will damage the cell.

BTW, I love my P90 for indoor games. It works so well for CQB. Can't beat the size and ergonomics.

 

[kitelights]

Not only can Kevin build the pack for you, but he can tack weld the straps on each cell for you so that you can do the final assembly safely yourself.

I know a lot of people do it with no problems, but soldering is not the intended method for joining cells. Your problem could be from the soldering, the short, or the charging. And now there's no easy way to find out what's damaged......

Good luck.