Battery fire that should have happened

[Diggs]

I've repaired computers for many years. (It was my business.) There was a time period when almost all laptops had the removable rear battery pack. That pack unusually consisted of six 18650 cells and a little BMS board. It wasn't uncommon for one or two cells to fail which shuts down the pack after a few minutes of run time. I replaced these packs for customers all the time so I had boxes of them. Back when I went to build my first e-bike battery those old computer packs were a free source of cells. I tore them apart, cycled them and then sorted on capacity. I soldered together my first 14s5p pack to use with a 1,000 watt generic hub motor and had a blast of a summer. Even though I rode it only a dozen or so "long" rides I noticed capacity was dropping by end of the summer. I stored it at half voltage for the winter. I got it out the next summer and even with a full charge it would die after 5 miles or so. I opened it up and this is what I saw -



Electrolyte was leaking from multiple cells across multiple cells. I'm actually surprised it didn't do much worse. I feel like I missed a bullet - whew! Thinking through things a bit more I had 2400mah cells paralleled with 1800mah cells (but both tested at 1600mah). Cells for computers need to be long and slow drain which is not the way I used them. Maybe soldering helped to weaken them although I have one more soldered pack still in service after 4 years (but with identical Panasonic cells) and doing well. I have switched to welding. I turned the pack in at the local county recycling facility. They had no idea what to do with it even though they accepted all batteries. That was the first Li e-bike battery they had seen and it was bare and leaking.

Anyways - I thought a few here may be interested in my beginners mistakes and what not to do.

 

[harrisonpatm]

Thank you for sharing. You are correctly (in my opinion) noting the three main mistakes you've since learned from: soldering instead of spot welding, unmatched parallel groups, and using low-drain cells for high drain application. Good to share so that others can hopefully learn.

 

[Diggs]

BTW - That local county recycling center had a fire that leveled several of their buildings a year or two later. They're not sure what caused it but are blaming it on lithium batteries.

I suppose the real bullet I dodged at the time was that my nephew had a CitiCar I could have. I think it ran on five lead-acid batteries (that of course were long since dead). Being in the computer repair business I could tap the supply of used computer battery packs from my friends and colleagues in the industry and convert it to run on 1,000+ 18650 cells. Making computer repair house calls with it tagged with my business logo would be good advertising. It's a project that never came to fruition and now I'm very glad it didn't.

 

[offGridDownUnder]

They had no idea what to do with it

That local county recycling center had a fire that leveled several of their buildings a year or two later

Hmmm.

 

[99zip99]

Drain the battery all cells to 2.0v with a headlight bulb a hair dryer. I'm trying to dead and check each cell group
Then you can take it to a recycling place AKA Staples home Depot ect. First Dead.

 

[Diggs]

Drain the battery all cells to 2.0v with a headlight bulb a hair dryer. I'm trying to dead and check each cell group
Then you can take it to a recycling place AKA Staples home Depot ect. First Dead.

I had drained it to 0.0 using a 120 volt 150 watt spotlight bulb. The pack was dead when they got it and this WAS the recycling center for all electronics especially batteries for the county. But like I said, this was quite a few years ago (and their fire was years later).

 

[neptronix]

Knowing what fails is as important as knowing what succeeds.
Thanks for sharing this with us, pardner!