Help w/ Severely Discharged Cells

[zeke_the_geek]

Long story short, I have (4) Eve 280K cells that were taken down to .4, .6, .7 and .9 volts. None of them are bloated - but they are in a compressed fixture. Sides/tops don't show signs of bloating.

Is there any hope of recovering these? I have a power supply that I can give them a specific voltage/amperage to see if they recover. Is this a lost cause? Recommendations?

 

[SomethingAppropriate]

We want the story.

 

[MrSparkle]

How long time have the cells been sitting below minimum recommended voltage?
Day, week, month, year?

 

[zeke_the_geek]

Cells have been that low for the past 4-8 weeks. I'm not sure of the exact time this happened. Basically, I "temporarily" connected a few things to the battery after the BMS - killing it and draining the cells.

 

[yabert]

taken down to .4, .6, .7 and .9 volts... Is there any hope of recovering these?

Sure. I've recovered LFP cells at 0.1V height years ago and they still work today.
Charge them slowly (1-2A) and they will came back over 2V in a short moment as there is almost no energy in LFP cells below 2V.

 

[zeke_the_geek]

Sure. I've recovered LFP cells at 0.1V height years ago and they still work today.
Charge them slowly (1-2A) and they will came back over 2V in a short moment as there is almost no energy in LFP cells below 2V.

What voltage to start? 3.2v / 1A?

 

[robby]

Is your bench power supply like this one.
Amazon
Set the current limit CC on the bench supply to 1 Amp and voltage limit CV to 3.2V
The voltage will start off low and eventually get up to 3.2V the current will start to drop off after many hours.
When it drops off close to 0 Amps and you can disconnect it, because it's charged to about 20%.
I have never had to do this for a dead LFP battery so maybe someone who has can give you some advice on getting it fully charged because 1 Amp @ 3.6V on a 280A battery would take an eternity.
You need to know the cell is still good and holding the charge before moving forward with a higher charge current and getting up to about 3.6V
Rinse and repeat for all four cells.

 

[Rednecktek]

but they are in a compressed fixture.

12v and 8a and just leave it assembled. Once it stops drawing current you should be good to connect the BMS back up, kick up the charging voltage, and let the BMS do its thing.

 

[Frank Blue]

I second robby for the bench power supply, good to have it.
Set current limit to a couple of amps (I use 1/100C) voltage limit 3.4V per cells just in case you forget everyhitng, raise current only when the cells left alone for 1 hour stay over 2.5V. It needs luck but may work and I am not aware of a best way to do that.

 

[fnnwizard]

Man, I just made a post today about completely shorting out some Lifepo4 batts years back. I only have data for the A123 smaller cells currently, but pretty sure they apply to "generics" also.

Anyway, after 1 year of continuous zero voltage (leads were soldered to batt to create dead short). After 6 months the cell SOH ~83% and after 1 year, 73%SOH. I can't remember if after 2 years or was it 3 that they were <%50 SOH. No temp control, they just sat in a garage for all that time. I'm going to see if I can get some of the pics. think it was around 2008 though.

I think the cells will be fine if not sat long. The first charge back is very high resistance so cells will heat more than normal. But I did my recharge at .5C back then. anything around .2C should be fine.

 

[zeke_the_geek]

Thanks everyone. I do have a bench power supply like robby mentioned. I just started w/ the first cell. 1A @ 3.2v. It's at 1.77v after about 3 minutes and rising slowly. I'll report back after the 4 cells have all gone through the process of getting them to 3.2v. Appreciate the assistance!

 

[MrSparkle]

Just a thought.
If all goes well and you are able to charge every cell up to 3.4V, leave all the cells for... I don't know, 3-4 weeks, but maybe even longer to check how big/small the self-discharge rate is?
After that, charge them all back to 3.4V discharge down to 3.0V to see how much capacity is left in them compared to when they were new?

 

[zeke_the_geek]

Update. After 29 hours - the first cell is still going. The power supply is at 3.2v and amperage has dropped to .525. Planning on pulling this one off when the power supply gets close to 0A. Slow going but hopefully this works.

 

[fnnwizard]

Update. After 29 hours - the first cell is still going. The power supply is at 3.2v and amperage has dropped to .525. Planning on pulling this one off when the power supply gets close to 0A. Slow going but hopefully this works.

A .1C charge rate (28A) won't hurt them and to save time just take them to 3.65V but stop when current gets to ~15A.

I'm about to do some test on 4 of the EVE LF280K (V3). I'll start a new thread after getting some data.
Initial charging right now.

I can't be on location so have to quickly setup a remote way to monitor and start/stop the charge.

 

[SirRoryO]

Hi All

I have just recently joined, as i have come into possession of some used Volvo BEV Li-Ion cells. I have very little information on the battery packs. but they are 6.5Kwh, 12s configuration and In want to guess they are 48v?

well currently reading them all together the packs are at 7.3v total, each cell roughly around 1.1v to 1.3v. I cannot remove the cells inside, they are prismatic but they are welded quite well to one another at the top.

My question is - If I use the same logic you have given for one cell, can I scale that to the whole pack? and by that I mean hitting it with around 42v at 6A? (3.5V per cell at 0.5A each?)

 

[rodrick]

Li-ion is more dangerous than Lifepo you might want to do this outside in a safe environment

have just recently joined, as i have come into possession of some used Volvo BEV Li-Ion cells. I have very little information on the battery packs. but they are 6.5Kwh, 12s configuration and In want to guess they are 48v?

12s typically would be 36 volt I would think double check everything you definitely don’t want to do something to cause a problem

 

[MrSparkle]

12s configuration and In want to guess they are 48v?

12s typically would be 36 volt

I object!
Li-NMC nominal ~3.65V, working range ~3.0V-4.2V (per cell).

12s - nominal 43,8V (usually labeled 44V).
Working range 36V-50.4V

NMC configuration for nominal 36V systems (30V-42V) is 10s
For nominal 48V systems would be 13s (39V-54.6V)
14s might be to high? (42V-58.8V)

Charging 12s NMC to 42V would only fill it up to half (50%) SoC.

 

[SirRoryO]

Thanks for the replys guys. Yes, I have went down a rabbit hole in the mean time and looks likely to be NMC. They are prismatic which seems to be made by CATL in china making these Geely cells.

Whats the likely hood if i was careful enough, getting these things back running? I want to side on the glass half full side, in my naive mind with these being EX Vehicle batteries they would be more robust? hahaha.

 

[wpns]

I have just recently joined, as i have come into possession of some used Volvo BEV Li-Ion cells. I have very little information on the battery packs. but they are 6.5Kwh, 12s configuration and In want to guess they are 48v?

well currently reading them all together the packs are at 7.3v total, each cell roughly around 1.1v to 1.3v. I cannot remove the cells inside, they are prismatic but they are welded quite well to one another at the top.

Well, if you are sure you want to mess around with them, do it outside or in a detached building. I'd get a variable power supply and limit the current to about an amp, set the voltage to 50V and see if the cells (very slowly) charge up and eventually get to the same voltage. Yes, it'll take around a week, but take it slowly and if one of the cells diverges more than about 25% from the others I'd stop and revise.

My question is - If I use the same logic you have given for one cell, can I scale that to the whole pack? and by that I mean hitting it with around 42v at 6A? (3.5V per cell at 0.5A each?)

Voltage adds in series, current adds in parallel, so that would be 42V at 0.5A, still perfectly safe numbers to get started with, though it may take a couple of weeks, and you'll still want to check them regularly.

 

[SirRoryO]

Thank you! For all the advice... I may have jumped to conclusions earlier... And I'm really scratching my head now... I decided to take the top off.... And it's not 12s...

 

[MrSparkle]

Yes, looks like 6s2p (2p6s? I have still not figure out what way is customary).
You could measure individual cells with multimeter (right on top where bus bars are welded) and write here all individual voltages?

 

[SirRoryO]

I will do exactly this tomorrow when I am back around that pack Im hoping for great news hahahaha

 

[user1385]

I will do exactly this tomorrow when I am back around that pack Im hoping for great news hahahaha

Hello Sir. I PM you can You please check. Regards

 

[SirRoryO]

Sorry to be a little late... But out of 20 packs.. I chose 2 packs to measure for this reply. It is correct that these packs are 2p6s I followed the Multimeter around showing when polarity was wrong. I expect these might be 24v packs in this case. And would have ran 2 in series to get the 48v system.

Here are the packs measured in the same way.

Overall,4.32v
From positive terminal back:
0.667
0.667
0.813
0.812
0.781
0.782
0.756
0.756
0.711
0.712
0.597
0.597

Overall 7.16v

1.216
1.218
1.221
1.221
1.268
1.268
1.153
1.153
1.032
1.032
1.280
1.280

 

[wpns]

Sorry to be a little late... But out of 20 packs.. I chose 2 packs to measure for this reply. It is correct that these packs are 2p6s I followed the Multimeter around showing when polarity was wrong. I expect these might be 24v packs in this case. And would have ran 2 in series to get the 48v system.

Here are the packs measured in the same way.

Overall,4.32v
From positive terminal back:
0.667
0.667
0.813
0.812
0.781
0.782
0.756
0.756
0.711
0.712
0.597
0.597

Overall 7.16v

1.216
1.218
1.221
1.221
1.268
1.268
1.153
1.153
1.032
1.032
1.280
1.280

What happens if you put an amp of current into them from a bench supply?