Help! What to do with waaaay overcharged cells?

[noenegdod]

So should I discharge them even lower? Bring them down to 3.4v??
They are currently sitting at 3.654v and not moving anymore.

If you had top balanced up to 3.65v held it there until current dropped off and not much was going in (relative to how big your pack is) and then disconnected, over the course of several hours/days the cells will drift down to somewhere around 3.4v

I honestly dont know what is best for you to do in the situation you are in right now. My gut says discharging them further is not a good idea. I think dipping below the "knee" runs the risk of unevenly discharging cells and ruining the balance.

I would not argue with @ Supervstech on his recommendation, it seems perfectly reasonable. Get it put together and in service.

 

[Smokin]

Leave the cells sit disconnected for 28 days. They will settle down to 3.3 volts. Then check them
In the early days of LFP they charged them to 4.2 volts. They didn't know anybetter. They discovered they was no advantage in doing so. It didn't add any more power. So someone decided that if you stop at 3.65 the battery was happy and there was alot less chance of inducing a phase change in the electrolite. YO, what he said,

 

[Smokin]

I watched at least 30 minutes of the video starting at 49:00 and don’t see anything relevant?

I really really hope I’ll be ok.
It took about an hour to get the voltage back down to 3.6v. That’s where they are currently sitting at and slowly rising since we removed the load.

start at 47:00 He explains it really well. You have to listen.

 

[TommyHolly]

If you had top balanced up to 3.65v held it there until current dropped off and not much was going in (relative to how big your pack is) and then disconnected, over the course of several hours/days the cells will drift down to somewhere around 3.4v

I honestly dont know what is best for you to do in the situation you are in right now. My gut says discharging them further is not a good idea. I think dipping below the "knee" runs the risk of unevenly discharging cells and ruining the balance.

I would not argue with @ Supervstech on his recommendation, it seems perfectly reasonable. Get it put together and in service.

Ok cool. My cells go down from 3.65v to 3.1 or even a few at 2.98v after just 10 days. They are 6 years old though and slightly abused.

I’ll put them back in. Glad to hear they are not dangerous or worthless

 

[noenegdod]

Ok cool. My cells go down from 3.65v to 3.1 or even a few at 2.98v after just 10 days. They are 6 years old though and slightly abused.

Do they do that just sitting there? No load, not connected to anything?

 

[TommyHolly]

Do they do that just sitting there? No load, not connected to anything?

Correct.
I posted my results above for a 10-day standing test after a full top balance by parallel connecting all of them.

After 10 days, the cells dropped from 3.65v to as low as 2.98v with no load, not connected to each other or anything.

The capacity tests mirrored the standing resistance tests. The capacity of the cells ranged from 91Ah to 83Ah.

 

[Horsefly]

After 10 days, the cells dropped from 3.65v to as low as 2.98v with no load, not connected to each other or anything.

Yikes. I think - independent of what we have all been saying in this thread - you have a problem. Those cells are damaged. I'm so sorry man.

 

[noenegdod]

Correct.
I posted my results above for a 10-day standing test after a full top balance by parallel connecting all of them.

After 10 days, the cells dropped from 3.65v to as low as 2.98v with no load, not connected to each other or anything.

The capacity tests mirrored the standing resistance tests. The capacity of the cells ranged from 91Ah to 83Ah.

Someone else please chime in but they should not drop that far that fast. Have you charged them, let them sit for 10 days and then done a capacity test?

 

[TommyHolly]

Yikes. I think - independent of what we have all been saying in this thread - you have a problem. Those cells are damaged. I'm so sorry man.

Correct. The cells are damaged. They are 6 years old and had no BMS on them or any kind of monitoring system when I purchased the boat. There was a leaky hatch above them dripping on them and they were sitting in 3” of water as well.

I top balanced, and then capacity tested all 48 of them over the course of 5 weeks. In the other thread here, we determined that they are still in useable condition. The capacities ranged from 82.9Ah to 92.1Ah. The average was about 85Ah. Well below the nominal 100Ah but still above the cutoff of 80Ah that everyone mentioned as considering them no longer useful.

 

[TommyHolly]

Someone else please chime in but they should not drop that far that fast. Have you charged them, let them sit for 10 days and then done a capacity test?

I performed the standing resistance test after top balancing them in parallel. Then connected them all together in parallel after the test was over and re-top balanced them again to prepare for the capacity test.

I performed the capacity test immediately after top balancing them in parallel. After that was finished, I top balanced them again getting ready for the final re-install when this accident happened.

 

[noenegdod]

I performed the standing resistance test after top balancing them in parallel. Then connected them all together in parallel after the test was over and re-top balanced them again to prepare for the capacity test.

I performed the capacity test immediately after top balancing them in parallel. After that was finished, I top balanced them again getting ready for the final re-install when this accident happened.

It they are being cycled every day I guess it is possible that they may be ok but here is the issue. Some where around 70-90% of all the energy storage lives in the 3.3xx volt range of the cell so if over the course of 10 days the cells go from 3.65 to 2.9, you have lost basically all of energy you have put in them.

They have no value other than pounding a bunch of energy into them during the day and withdrawing it over the course of the night.

With the rate that they are self discharging it is a wonder that you even managed to "top balance" them with only 20 amps.

 

[TommyHolly]

It they are being cycled every day I guess it is possible that they may be ok but here is the issue. Some where around 70-90% of all the energy storage lives in the 3.3xx volt range of the cell so if over the course of 10 days the cells go from 3.65 to 2.9, you have lost basically all of energy you have put in them.

They have no value other than pounding a bunch of energy into them during the day and withdrawing it over the course of the night.

With the rate that they are self discharging it is a wonder that you even managed to "top balance" them with only 20 amps.

Oooops, sorry I have so much going on, that I gave you the wrong readings. (I posted the correct ones above though.) The bad readings I gave you were from two bad cells that we took out of the system.

After 12 days, the majority of the 48 good cells I tested in the standing resistance test went from 3.65v down to 3.600v with the worst being 3.598v. So they only lost 0.05v after 10 days.

Sorry about the confusion.

 

[Horsefly]

Oooops, sorry I have so much going on, that I gave you the wrong readings. (I posted the correct ones above though.) The bad readings I gave you were from two bad cells that we took out of the system.

After 12 days, the majority of the 48 good cells I tested in the standing resistance test went from 3.65v down to 3.600v with the worst being 3.598v. So they only lost 0.05v after 10 days.

Sorry about the confusion.

Ok, that is much better. It didn't make sense that you were getting 80% Capacity out of cells that dropped on their own to below 3.0V.

So I think we are back to your cells are probably fine, and you shouldn't need to do anything more to them before putting them in service.

 

[Shale MacGregor]

Oooops, sorry I have so much going on, that I gave you the wrong readings. (I posted the correct ones above though.) The bad readings I gave you were from two bad cells that we took out of the system.

After 12 days, the majority of the 48 good cells I tested in the standing resistance test went from 3.65v down to 3.600v with the worst being 3.598v. So they only lost 0.05v after 10 days.

Sorry about the confusion.

That is surprisingly high after 12 days, sounds good to me. I would have expected them to be down in the 3.4 range.

People will shout you down but these cells can take 4.2V as a maximum charge, there just isn't much benefit to going beyond 3.5V At 4.27 you might have started breaking down some of the electrolytes but I would keep on trucking at this point.

 

[Shale MacGregor]

Oh and to chime in, once you get up much over 3.5 and amps start dropping, don't waste days trickling it, I have done multiple tests and unless I slap them on the capacity tester right at 3.65 I can't even measure a difference. Fractions of a percent aren't worth worrying about.

 

[TommyHolly]

That is surprisingly high after 12 days, sounds good to me. I would have expected them to be down in the 3.4 range.

People will shout you down but these cells can take 4.2V as a maximum charge, there just isn't much benefit to going beyond 3.5V At 4.27 you might have started breaking down some of the electrolytes but I would keep on trucking at this point.

Hey thanks! That’s really good to know.

I’ve since reinstalled the LiFePo4 cells in thier new 3P-4S configuration. Each 300Ah battery having its own overkill Solar BMS and onff switch.

They’ve passed the stress test with flying colors!! I’m so happy this nightmare on my boat is finally over with. I was able to stress test with a portable air conditioner, a George Forman grill, multiple fans, an ice maker, charging laptop and more. I ran all of those for an hour and barely noticed anything. The inverter 350A fuse got up to 64°C and that was it. Everything works solidly. No stress no worries and totally dependable.

Originally I couldn’t even run the single air conditioner by itself. The cells were all damaged, sitting in 6” of water, no BMS or any kind of monitoring.

I was worried about the 12 hours of over charging up to 4.27v but because it was such a momentary thing at such a low 0.2A per cell charge, it didn’t cause any noticeable damage.