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Old 02-27-2021, 09:13 PM   #11
Pat911
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Default Re: Emergency Dead Lithium Help

Why can’t you get identical cells?

I think the bigger question though is why the BMS didn’t protect your pack unless it was the BMS itself that drained it, although that is unlikely as the BMS current drain should be minuscule.

Cheers
Pat.
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Old 02-28-2021, 12:06 PM   #12
Silenttrouble
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Default Re: Emergency Dead Lithium Help

The answer is I'm not sure.

The BMS was properly setup and should have protected it.

I need to double check my wiring again because the only answer to this question I can come up with is that I screwed up and put a load on the battery side of the contactor. I didn't Think I did but I'm going to verify again before I reinstall another battery pack. The other option and less likely, is that the BMS was shut off with a load.

As far as identical cells. I can't find these cells, they weren't a great or ideal setup anyway it was an absolute nightmare to build with the short tabs that had been cut from the original bar. Not to say I wouldnt be able to or willing to do it again, but honestly if I found a better solution for similar price i'd go that route.
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Old 02-28-2021, 05:46 PM   #13
Pat911
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Default Re: Emergency Dead Lithium Help

Hi Silenttrouble,

With all the warnings and caveats given earlier in this thread, it is possible to try and revive your existing setup if you want to give it a go. I would definitely NOT try to revive the entire pack at once, your cells are too far out of balance and too much heat may be generated.

You will need a laboratory style power supply with adjustable voltage and current. 3 amps will be enough. This will be a slow process.

Take the pack out of the cart and put it outside where it is clear of anything combustible, just in case. Disconnect/remove the BMS. If possible, disassemble the pack into individual cells.

Set your power supply to 3.2v and 1A maximum. Charge each cell one at a time until the charge current drops to around 0.5A. Monitor the temperature of the cell. It may become warm, which is ok, but if it becomes too hot, especially to touch, or swells, then stop. That cell will be too dangerous to reuse and should be discarded.

If that process goes well, increase the voltage to 3.7v and current to 2A. Charge until current drops to 0.5A and continue monitoring as before. If all is still good, increase the voltage to 4.2v and current to 3A. Charge until current drops to 0.5A and continue monitoring as before. If this last stage goes well, then let that cell sit and check it’s terminal voltage every few hours. It shouldn’t drop much.

Repeat the above for all 14 cells. Once the process is complete, the terminal voltage of all cells should remain fairly balanced. If this is the case, the pack can be reassembled and reinstalled into the cart. Check performance hasn’t deteriorated too much.

The danger you risk now is possible fire when recharging in the future, especially the first few times. Discharging isn’t a problem. Since you monitored the cell for heat during the revival process, the risk of fire is reduced, but not eliminated.

I would never charge that pack indoors, and preferably never unattended. What current is your existing charger? As an extra safety measure, it would be wise to charge slower than before. I would also investigate why your BMS failed to protect the pack.

Caveat Emptor.
I have given you all the warnings and the process I described above will minimise the risk in reviving your pack but will not eliminate it. Your pack will never be 100% safe to use, but the more successful recharges the pack goes through, the more confidence you can have in it. In fact, if practical, it would be wise to remove the pack from the cart, keeping the BMS connected, and place it outside the first few times it’s recharged until you gain confidence in it. The first 5 or 10 times at least.

Good luck
Pat.
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Old 03-01-2021, 01:56 PM   #14
emoney
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Default Re: Emergency Dead Lithium Help

Probably best to use a Benchtop Power Supply to attempt this on each cell? Something with CC/CV that you can control the amt of amps going to the cell like Pat911 laid out.
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Old 03-01-2021, 02:09 PM   #15
DaveTM
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Default Re: Emergency Dead Lithium Help

I just have to comment on any attempt to revive a pack that has obviously gone well below the minimum voltage on every cell in the pack.

I get the "want" to just fix the existing pack as that is far less costly, and more importantly far less work to fix it.

However, these batteries simply have a very high probability of "goin south" when this type of incident occurs. Even if you revive the pack and proceed with caution on charging it outside the garage\home, you still have a high probability of a catastrophic event.

Isn't it less costly to replace the damaged pack with a working good one? If the batteries reach thermal runaway, you not only lose the pack, but you will also likely lose the entire cart! You have a lot of $$$ sitting there in a controller, tires, wheels, seats, BMS.

I can't see any long term safe benefit of reviving a set of toasted lithium batteries.

MHO
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Old 03-01-2021, 04:22 PM   #16
Pat911
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Default Re: Emergency Dead Lithium Help

Hi DaveTM,

I absolutely agree with you. I gave plenty of warnings prior to and in my post and I seriously considered not publishing the information, but I thought that as there is a lot of misinformation around, I should probably describe a process that would make the revival procedure safe and give the best possible chance of a long term successful outcome.

Monitoring the cells temperature and physical appearance during the first charge is critical. Silenttrouble’s LG cells are pouches without any casing, so checking for swelling is very easy for him.

Cheers
Pat.
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Old 03-02-2021, 08:10 AM   #17
bronsonj
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Default Re: Emergency Dead Lithium Help

There are so many options available now that if it were me I'd just build a new pack. There's these cool lithium modules out of the Fiat 500e, the Ford Escape hybrid lithium cells (they come in two sizes, 5amp and 26 amp) the 26 amp would make a cool 14S4P pack. There's the coolest ones, the newest Gen 3 leaf cells (2019 and newer I think) that are incredibly compact and powerful.

I have heard (rarely, but does happen) that the BMS can fail and when they fail they often fail in a shorted state = to the balance current drain. So if it tries to balance the cells with a 1 amp drain, then when it fails it will put a 1 amp drain on the cell. I have no idea if that's the cause of your parasitic drain, but if it were me I'd look at a pack disconnect to protect it from future drain situations. $0.02
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Old 03-08-2021, 11:28 AM   #18
Silenttrouble
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Default Re: Emergency Dead Lithium Help

I've decided not revive. I'm struggling to find a suitable replacement now though. It was a custom pack that fit nicely into the cart. I cant seem to find those cells anymore and honestly I wasn't that happy with the pack build anyway.

Now to find cells that will work.
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Old 03-08-2021, 01:09 PM   #19
DaveTM
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Default Re: Emergency Dead Lithium Help

I think that's a wise choice.
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Old 03-09-2021, 03:45 PM   #20
Bama Brad
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Default Re: Emergency Dead Lithium Help

Quote:
Originally Posted by DaveTM View Post
I think that's a wise choice.
I second that! Move on without worries! Few years from now, just a faded memory--better than a catastrophic event like losing your cart (or house, or life).
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