Bad charger killed my battery pack :(

i did a while ago a battery pack using 12x 18650 trustfire 2400mah (the flame one) in 3s4p conf.

using for a year in a video light, that pull about 0.5C from each battery. all working fine, and batts seems healthy with great run-times.

but a month ago, i noticed the last 2 series of batteries having a lower voltage, like 4.2v, 4.0v, 4.0v, right of the charger (the pack have a led voltmeter)

until last night the light went off about 30% of the normal run-time. the protection circuit of batteries has tripped off.

trying to find the cause, disassembled the pack and measured each battery. most of them looks like they got a high internal resistance, im getting only 600mah from some of them (discharging at 1A). after fully discharged, the voltage goes up, but more than usual, like 3.8v, wich i believe tell it have developed as imagined a really high internal resistance.

as i did other packs with the same type/model of batteries, and all of them are working fine, i wondered if the charger was to blame.

as at the time i didn't have a proper hobby charger (my partner was using, not me), i used the only one i had in hands, a small e_sky charger/balancer that came with my RC helicopter. it charges at 0.8A. very low, i know, but i didn't have options back then.

at closer inspection, i opened the charger and guess what? 2 IC's and one diode where blown up!



well, better the charger be the problem, as i like the batteries

so, to sum up, my questions:

how the charger could kill them so fast like this, even if all batts had protection circuit?

Protection circuit is only the last failsafe between you and exploding/venting cell!! Remember that - people tend to handle protected liions like ni-cd - discharge to zero V (protection cutoff) and charge directly from USB 5V - It has protection circuit right? So what could happen?

It shuts down at 2,7V and 4,35V if I remember correctly (i have the same batteries). And 4,35V can kill liion battery quite fast. But stragne is, all batteries are affected.

malow said:

how the charger could kill them so fast like this, even if all batts had protection circuit?

Click to expand...

Sorry to see the misfortune with your charger and batteries.

However protection circuits are only there to save the batteries from catching fire. They cannot prevent bad charging from causing damage.

example of discharge... 578mah...



its not a discharge curve, its a discharge "free fall" ;P

I wonder how that charger charges now with blown diodes and, what are those scorched ICs?

I also own that same charger. It must have pretty tiny margins, as the manual strictly forbids connecting to car electrical system with engine running.

i tried to find datasheet for those IC's, found absolutely nothing.

the heat melted a hole in the bottom part of the charger. the weird part? looks like there's a LM35 (temperature IC) on the board ;P

i'm testing the rest of batteries, some got only 70mah at 1A discharge... 70mah!!!!!

at least now i got a bunch of protection circuits...