Charging a LiFePo4 battery after a few years? - Page 1
Forum section: electronics / general

author: MaxSimmonds
author_rank: Contributor
timestamp: November 22, 2020, 03:28:05 pm
content: Hey guysI have an old ebike battery I'd like to use for a DIY ebike controller I'm designing. It's been left for a few years - would it be safe to attempt to charge it?It was made by Vpower.hk, who I believe have now gone bust. It came with a 6A charger, and it's a 48V battery (13 cells, I think?). I used it for a uni project about 3 years ago, I probably only charged it once in that time, at the beginning, and then left it. Given my huge lack of knowledge on batteries, I'm a bit worried to simply plug the battery into the charger and charge it, in case it catches fire (I live in a rented flat, top floor, so slightly concerning).The open circuit voltage is around 41V, I switched it on (it has a isolation switch on the outside) for a few seconds to measure it, again, concerned it may overheat and catch fire.Am I being too cautious? Will it be fine to attempt a charge? I'm fairly confident the battery might be dead, given how long it's been left, but is it safe to give it ago?Sorry I can't give any more info on the battery, there's no websites or anything now to find the data on it, I know it had current limiting, and there's some electronics inside (hopefully undervoltage protection?).Thanks!

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 22, 2020, 04:10:47 pm
content: Charge it slow and check that all the cells are roughly in balance.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 22, 2020, 05:06:57 pm
content: I'm assuming it has a BMS.Assuming good cells and non-broken-by-design BMS, there is absolutely no concern. Just plug it in.OTOH, assuming crappy cells and/or broken-by-design BMS, it may blow up; but this situation hasn't changed from initial. If it is crap now, it was crap already back then, and could have blown up then as well.

author: tunk
author_rank: Super Contributor
timestamp: November 22, 2020, 05:35:57 pm
content: Open it and check the voltages of each cell.The nominal voltage of LiFePo4 is 3.2V, so there should be 15 cells.

author: MaxSimmonds
author_rank: Contributor
timestamp: November 22, 2020, 06:56:09 pm
content: Okay I think I'll open it up and see what the cell voltage. What would it mean if one cell is much lower than the others?Thanks guys

author: sandalcandal
author_rank: Unknown
timestamp: November 23, 2020, 02:41:08 am
content: Quote from: MaxSimmonds on November 22, 2020, 06:56:09 pmIt means a series group has cactus or less likely but still problematic the BMS is faulty.Quote from: tunk on November 22, 2020, 05:35:57 pmIt might not be LFP for an ebike battery. If you count 14 or less in series it will be non-LFP assuming the 48V rating is accurate. If voltage is zero as it could be due being drained by the BMS or faulty cells then I'd consider not using it or do some very cautious recharging and checking. Otherwise as long as voltage is above 3.0V it should be safe or as a safe as a battery pack from a defunct Chinese manufacturer can be...Edit: Since you've got decent voltage it should be ok but would be prudent to do a cycle test (drain it under some dummy load then recharge) and check voltage of cells as you go with some fire safety on hand.

author: MaxSimmonds
author_rank: Contributor
timestamp: November 23, 2020, 11:22:49 am
content: I think it was sold as a LFP battery pack - but I'll measure the cell voltages out of curiosity. I opened up the case a few weeks back and saw some electronics, and also all the cells wrapped up in tape so I decided to stay away from them, I might carefully cut the tape and measure the voltages.What's the best defence against a lithium fire? My thought's is something to suffocate the flames, like a tin box or something?Thanks again!

author: Siwastaja
author_rank: Super Contributor
timestamp: November 23, 2020, 12:57:15 pm
content: LARGE container of water where the whole pack fits. Preferably made of metal. Preferably with wheels so you can push it out of the door. Preferably street-level door...Or, as you suggest, just a metallic box is already better than nothing, at least it prevents direct torch effect from immediately hitting your curtains. But smoke isn't fun, and you can't "suffocate" li-ion fire by removing source of air, it has internal source of oxygen (in case of LiFePO4, it's in the form of phosphate, which isn't released too easily, but it's still possible). So the metallic box, if good enough, may save your house, but you still need immediate evacuation and the fire brigade to handle it as a potential house fire.Water container has the ability toactuallystop the fire within some minutes (depending on how well the water penetrates the pack casing and starts actually cooling the cells).And remember that it isn't lithium fire. Completely different thing, completely different mitigations and actions. Be careful with the terminology, because lithium fireisa real thing and the actions required are the opposite. If you call the emergency services with "I have a lithium fire", they get wrong instructions which doesn't help.