Well my first built pack almost died in a flame

nethern

1 mW
Joined
Feb 3, 2018
Messages
18
I finish riding from work. The juice was almost out. I took It out to meter each cell to see is any one had problem because i realize there had been a sudden power lost during the ride.

I put It on the table, taking multimeter to test the first group cells. I realised the first group that connects the positive output. So, i started with the first group. First one was dead, second one also dead. When i touched the third one, there was a spark. I was surprised a bit, then resumed measureing. I Did not know when i Did wrong when i have one of the probes touch the third cell again, The nickel strip started to turn red. A small flame went off. I quickly took It outside and back to grabed the Fire extinguisher. The Fire was off when i came back. I carefully cut the wire Than is still connect to the group.

i wonder where went wrong?i have tested the cell many times before, no problem. Why This time?

Please help me. I dont want This happen next time
IMG_20180320_181611.jpg
 
Could be a lot of things, including the damaged BMS and possibly cells you presumably still haven't repaired from here:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=92683
(since you never came back to that thread, we have to assume nothing else was fixed so the pack is still damaged).

A common problem with DIY packs is not putting insulators under the nickel where it crosses the edge of the positive ends of cells. Without those, pressing on the nickel strips with your probes could cause them to touch damaged areas of shrinkwrap and then the actual cell itself, shorting across teh cell (and thus the whole parallel group).


BTW, if cell groups are actually dead, then you need to replace them. Then you need to either fix or replace the BMS that is allowing them to die, and/or modify your riding style and distance to not kill them, or you'll end up replacing them often, which will get expensive.
 
Yeah, the battery pack worked good to me after the initial drain from that post.

Looks like i need to rebuild the battery with insulator and new bms. I need to do It anyway because 1)i need to fit in a different shape of bag - rectangle one. 2) the current bms has separated charge/discharge port with i dont like.

And Yes, i Did push Hard to 30a a few times. So, It will normally kill the first group in the series?

Is It possible to test if other cells are damaged? Like maybe resistance?
 
It s 15s4p. Planned to build two of them and parrallel connect to 8p.

I uses vtc6. not sure if genuine but looks like genuine - with quality packing for each cell. not cheap for the two packs
 
amberwolf said:
A common problem with DIY packs is not putting insulators under the nickel where it crosses the edge of the positive ends of cells. Without those, pressing on the nickel strips with your probes could cause them to touch damaged areas of shrinkwrap and then the actual cell itself, shorting across teh cell (and thus the whole parallel group).
from memory It seems the only cause i Can think of. The green wrap of cell might damaged from heat and allowing contact with nickel strip when i press probe on it.
i will put on the insulator next time. Good learning time
 
Bummer dude. Those look like Sony cells? Sounds like you'll be able to salvage the battery or cells at least.
 
Must have been a short of course. Possibly when you pushed on the strip, it contacted and spot welded itself.

A hot enough pack could melt the shrink, allowing a short on the positve end of a cell. Shorting the positive to the negative can of the same cell. I have a suspicion this is how my battery burned my house. While charging a cell got hot, melted the shrink, and once contact was made, the shorted cell overheated starting the battery fire.

Most likely this scenario was initiated by a bms fail that allowed the overcharge, heating the cell. I'll never know, but that is a plausible reason why a perfectly good pack suddenly decides to burn my garage down.
 
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