Postmortem - Ebike pack

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Oct 30, 2019
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My very first ebike battery pack (14s5p from used laptop batteries) has had declining performance over the summer. Pull on it hard and the 45A BMS trips due to low voltage. I was going to put a 20A BMS on it for the remainder of its old age but when I opened it up I saw extreme cell leakage in eight different places and was more than surprised. Voltage is at 54.4V which should be about 75% charge. First wondered if it happened on charge (suspected but the BMS appears fine) or discharge. Then again, the electrolyte is at the top of the pack and the only time the pack was upside down was in storage. Things that make you go hmmm.....

pack1.jpg
 
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To be flat out honest - that looks extremely dangerous. Especially knowing there is leakage, I would immediately discharge it before fire happens...

It's generally not a good idea to mix random cells like that on high-drain applications such as an eBike. You end up with some cells working harder than others, thus getting hotter, degrading faster, etc. If you build another, consider buying or borrowing a spot-welder and also putting the adhesive insulator discs on the positive side for extra insulation.
 
4-5years is alot i would say. especially if you have pushed it as hard as you have. Note that laptop cells arent made for high current drain. Especially not if been used allready.

I use 2nd hand cells like this to but rarely get more than 1 year out of them when pushed. They basically die hard like you seen now.
 
daromer said:
I use 2nd hand cells like this to but rarely get more than 1 year out of them when pushed. They basically die hard like you seen now.
Click to expand...

Well then I feel pretty good about them. They were on a "guest" bike after the first year so wasn't ridden often but the rides were 20-25 miles each time. I guess the term applies they were rode hard and put away wet - heh!
 
I feel bad for that old pack. :cry: It got me started in ebikes. I use a 65 watt (110v) incandescent light bulb for discharge and here it is 24 hours later still glowing away out in the shed (@28°F). It appears that pack was a great first effort of mine. RIP heh....
 
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