Help! What to do with waaaay overcharged cells?

[TommyHolly]

I was ready to re-install my CALB LiFePo4 system. I had the cells all top balancing for the last 2 weeks charging at 3.65v and all 48 cells connected in parallel. They were already at 3.65v for over a week now.

My wife loaded up the storeroom with cases of water where the batteries are and bumped into the voltage knob. It got cranked up to 9v!!! She didn’t know. We just caught it now.

My variable voltage charger only goes to a maximum of 10A luckily. It spent 12 hours charging at 9v with 10A. Aaaaargh

The cells are now all testing at 4.27v with a multimeter. The max rating for CALB is 3.65v.
I immediately put a 6v heater on it to draw down the power. Also I have my 180w capacity tester which draws a max of 30A on there as well. We got them down to 3.82v after 30 minutes (testing with a load on them)

My important questions are:
1. Are these batteries still useable and trustworthy or are they done? Again, they were only overcharged for 12 hours.

2. Is it ok what I’m doing lowering the voltage with a 30A 180w capacity tester and a 6v heater tester?

3. Do I need to capacity test all of these cells again? It took me 2 months the last time. I don’t want to do that again if possible.

 

[Smokin]

You should be ok.
47:00

 

[Horsefly]

1. How many cells did you have in parallel? Looks like a ton of them. Divide the number of cells into 10A, and that is how much was going into each cell.
2. Was the 4.27V measured right after you discovered the problem, or had they been disconnected for a while?
3. I see two of the 30V 10A power supplies. It sounds like you were only using one of them?
4. Are the cells swollen?

Depending on the answers (and going only on what it looks like) I think there is a pretty good chance you are OK. LFP is pretty tolerant of over-charging. If you really do have lots of cells, when the voltage suddenly went up to 9V the power supply probably went into constant current mode and was raising the voltage slowly over that 12 hours. If the current per cell was in the 10's of mA, the voltage wasn't going up very fast.

It is possible that you might have lost a little bit of cycle life, but probably not much.

 

[TommyHolly]

We got the voltage down to 3.7v after 40 minutes. Keep in mind this is with the load attached.

I plan to first disconnect the 6v heater battery tester when we get closer. Then leave the 180w capacity tester connected set at a 30A load (80w). I have it set to stop at 3.6v

Then I plan to let the cells sit for 24 hours and see what happens.

 

[TommyHolly]

1. How many cells did you have in parallel? Looks like a ton of them. Divide the number of cells into 10A, and that is how much was going into each cell.

I had 48 cells connected in parallel. So 10A divided by 48 cells equals 0.208A going into them for 12 hours.

1. Was the 4.27V measured right after you discovered the problem, or had they been disconnected for a while?

The 4.27v was measured the second I discovered it an hour ago. I immediately hooked up a load to bring them down. After over an hour I got them down to 3.685v and I’m going to let them sit at that for a while.

1. I see two of the 30V 10A power supplies. It sounds like you were only using one of them?

Only one of the variable voltage chargers got turned up. When that happens, the other immediately kicks off because the other was correctly set at 3.65v.

1. Are the cells swollen?

The cells were already swollen before this happened. So no change. They aren’t hot and don’t look different.

Depending on the answers (and going only on what it looks like) I think there is a pretty good chance you are OK. LFP is pretty tolerant of over-charging. If you really do have lots of cells, when the voltage suddenly went up to 9V the power supply probably went into constant current mode and was raising the voltage slowly over that 12 hours. If the current per cell was in the 10's of mA, the voltage wasn't going up very fast.

It is possible that you might have lost a little bit of cycle life, but probably not much.

That’s great news!!

 

[TommyHolly]

You should be ok.
47:00

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.

 

[MurphyGuy]

Fire up the video camera on the back lawn and keep charging...

 

[noenegdod]

They were already at 3.65v for over a week now.

Why would you leave them at 3.65 for a week. When they reach 3.65, they are done. Disconnect and move on.

 

[Horsefly]

Why would you leave them at 3.65 for a week. When they reach 3.65, they are done. Disconnect and move on.

I would say it is OK - even good - to leave it at 3.65V until the current has dropped down significantly. But I do agree that would happen pretty quickly, and certainly would not take a week.

 

[noenegdod]

I would say it is OK - even good - to leave it at 3.65V until the current has dropped down significantly. But I do agree that would happen pretty quickly, and certainly would not take a week.

Ya, I guess that wasn't crystal clear. I assumed (which I shouldnt do) that everyone knows that at this point. With 48 cells though even once current has dropped to 5 amps I would tend to think your there.

 

[TommyHolly]

Why would you leave them at 3.65 for a week. When they reach 3.65, they are done. Disconnect and move on.

Because there was always amps still being drawn. To top balance just one cell, it usually took about 4 hours to get that final 3.64v turn into a 3.65v, there was 0.017A still going into the batteries. It slowed down once it got down to 0.250A.

I would keep the charger on until it would show 0.000A. And when you leave the cells without a charge, they slowly go down because of internal resistance.

Before I did a capacity test, I did a standing resistance test and after a week the batteries went down from 3.65v to 3.61v in just a week!

 

[TommyHolly]

What do you guys think about this plan?
Now that the cells are around 3.55v after putting a load on them, let them sit for a day or two, then recharge them back up to 3.65v?

Sound good?

 

[Horsefly]

I would keep the charger on until it would show 0.000A. And when you leave the cells without a charge, they slowly go down because of internal resistance.

I think what @noenegdod and I are agreeing on is that you don't need to get it all the ways to 0A.

Once fully charged, they will "settle" down to something like 3.4V (depends on the cells), but are still fully charged. It isn't because of the internal resistance. The self-discharge of something like 1-2% per month is due to internal resistance.

 

[noenegdod]

Because there was always amps still being drawn. To top balance just one cell, it usually took about 4 hours to get that final 3.64v turn into a 3.65v, there was 0.017A still going into the batteries. It slowed down once it got down to 0.250A.

I would keep the charger on until it would show 0.000A. And when you leave the cells without a charge, they slowly go down because of internal resistance.

Before I did a capacity test, I did a standing resistance test and after a week the batteries went down from 3.65v to 3.61v in just a week!

Ya my friend, you were done a long time ago (days).

Its not internal resistance, its voltage difference that is slowing the process down. At 10mv difference between charger and cells there simply isnt that much current that can flow into one cell. But if you multiply that 0.017a by the 48 cells you are charging you are still seeing 0.816a going into the whole pack.

What do you guys think about this plan?
Now that the cells are around 3.55v after putting a load on them, let them sit for a day or two, then recharge them back up to 3.65v?

Sound good?

Sure, but dont hold them there until 0 current. As said above, personally, Id stop when current hits 5 amps? maybe 2. In truth, you are "top balanced" well before you get to 3.65 volts (Like at 3.60).

 

[Supervstech]

What do you guys think about this plan?
Now that the cells are around 3.55v after putting a load on them, let them sit for a day or two, then recharge them back up to 3.65v?

Sound good?

No…
I would connect the parallel set, and arrange your BMS connect to load, and put them in service.
I would NOT charge them back to 3.65

Hey all made it up to full, and they all dropped to 3.55 which is a fine top balanced goal.
Just assemble them and get them working.

 

[TommyHolly]

I think what @noenegdod and I are agreeing on is that you don't need to get it all the ways to 0A.

Once fully charged, they will "settle" down to something like 3.4V (depends on the cells), but are still fully charged. It isn't because of the internal resistance. The self-discharge of something like 1-2% per month is due to internal resistance

They don’t settle at 3.64v
They continually drop at a steady rate.
Here is the results of my “Standing Resistance Test”, after charging the batteries for a week to 3.65v until the Amps read 0.000A, and then simply disconnecting them all from each other and recording the results:

DATE and TIME results taken in order:
12AUG 15:30
13AUG 11:20
13AUG 15:40
14AUG 09:30
16AUG 8:10
16AUG 15:15
17AUG 08:45
18AUG 09:15
18AUG 15:50
19AUG 09:50
20AUG 08:50
20AUG 15:15
21AUG 09:30
23AUG 08:15

First I list the battery number: (in this example Cell number #16 was first reading at 12AUG at 15:30 was 3.64v) *I didn’t start recording 3 digits until the 3rd reading.

16 3.64 3.64 3.64 3.639 3.632 3.630 3.628 3.624 3.623 3.621 3.618 3.616 3.614 3.608
36 3.64 3.64 3.637 3.632 3.620 3.617 3.614 3.608 3.606 3.602 3.598 3.596 3.593 3.584

32 3.64 3.64 3.639 3.636 3.627 3.625 3.622 3.617 3.616 3.613 3.609 3.608 3.606 3.598

4 3.64 3.64 3.638 3.634 3.624 3.623 3.620 3.615 3.614 3.611 3.608 3.607 3.604 3.598

5 3.64 3.64 3.638 3.634 3.624 3.623 3.620 3.615 3.614 3.611 3.608 3.606 3.604 3.598

15 3.64 3.64 3.637 3.632 3.622 3.620 3.617 3.612 3.611 3.608 3.604 3.603 3.600 3.594

10 3.64 3.64 3.637 3.633 3.623 3.621 3.618 3.613 3.612 3.609 3.606 3.604 3.602 3.596

6 3.64 3.64 3.638 3.634 3.625 3.623 3.621 3.616 3.615 3.612 3.608 3.608 3.605 3.599

34 3.64 3.64 3.637 3.634 3.624 3.622 3.619 3.615 3.614 3.611 3.608 3.606 3.604 3.598

31 3.64 3.64 3.635 3.630 3.619 3.617 3.614 3.608 3.608 3.604 3.600 3.599 3.596 3.590

22 3.64 3.64 3.637 3.633 3.623 3.622 3.619 3.614 3.614 3.610 3.607 3.606 3.604 3.597

46 3.64 3.64 3.639 3.635 3.625 3.623 3.620 3.614 3.614 3.610 3.606 3.604 3.602 3.594

1 3.64 3.64 3.638 3.635 3.625 3.623 3.621 3.616 3.615 3.612 3.609 3.608 3.605 3.599
18 3.64 3.64 3.638 3.634 3.624 3.623 3.620 3.616 3.614 3.612 3.608 3.607 3.604 3.598

12 3.64 3.64 3.637 3.633 3.623 3.622 3.619 3.614 3.614 3.611 3.607 3.606 3.604 3.598
24 3.64 3.64 3.639 3.635 3.627 3.625 3.623 3.618 3.618 3.615 3.612 3.611 3.609 3.603
3 3.64 3.64 3.637 3.634 3.624 3.622 3.619 3.614 3.613 3.610 3.606 3.605 3.603 3.596

2 3.64 3.64 3.637 3.633 3.623 3.621 3.619 3.614 3.613 3.610 3.607 3.605 3.603 3.596
23 3.64 3.64 3.638 3.634 3.625 3.623 3.621 3.616 3.616 3.613 3.609 3.608 3.606 3.600

47 3.64 3.64 3.636 3.631 3.621 3.619 3.616 3.611 3.610 3.606 3.603 3.602 3.599 3.592

40 3.64 3.64 3.638 3.633 3.624 3.622 3.620 3.614 3.614 3.610 3.607 3.606 3.603 3.597
7 3.64 3.64 3.637 3.633 3.622 3.620 3.618 3.612 3.612 3.608 3.604 3.603 3.601 3.594
39 3.64 3.64 3.636 3.632 3.621 3.619 3.616 3.610 3.609 3.606 3.602 3.600 3.598 3.591

14 3.64 3.64 3.637 3.632 3.622 3.620 3.617 3.612 3.611 3.608 3.604 3.603 3.600 3.594

28 3.64 3.64 3.638 3.635 3.626 3.625 3.622 3.618 3.617 3.614 3.611 3.610 3.608 3.602

37 3.64 3.64 3.64 3.639 3.632 3.631 3.629 3.625 3.625 3.623 3.620 3.619 3.617 3.612

35 3.64 3.64 3.639 3.636 3.627 3.626 3.623 3.619 3.618 3.616 3.612 3.612 3.609 3.604
29 3.64 3.64 3.639 3.637 3.629 3.627 3.625 3.621 3.620 3.618 3.614 3.614 3.611 3.606

30 3.64 3.64 3.634 3.629 3.618 3.616 3.612 3.607 3.606 3.602 3.598 3.597 3.595 3.588
17 3.64 3.64 3.637 3.632 3.622 3.620 3.617 3.612 3.611 3.608 3.604 3.603 3.601 3.594

39A 3.64 3.63 3.626 3.618 3.600 3.597 3.592 3.584 3.582 3.578 3.572 3.629 3.645 3.614

40A 3.64 3.63 3.624 3.615 3.595 3.592 3.587 3.579 3.577 3.572 3.567 3.47 2.960 3.641
45 3.64 3.64 3.635 3.630 3.619 3.617 3.614 3.609 3.608 3.605 3.601 3.600 3.597 3.590
13 3.64 3.64 3.636 3.631 3.620 3.618 3.614 3.609 3.608 3.605 3.601 3.600 3.598 3.590

25 3.64 3.64 3.638 3.634 3.625 3.623 3.621 3.617 3.616 3.613 3.610 3.609 3.607 3.601
38 3.64 3.64 3.639 3.636 3.627 3.626 3.623 3.619 3.618 3.616 3.613 3.612 3.610 3.604

26 3.64 3.64 3.637 3.633 3.623 3.622 3.619 3.614 3.614 3.611 3.607 3.607 3.604 3.598

48 3.64 3.64 3.64 3.638 3.629 3.628 3.626 3.622 3.621 3.618 3.615 3.614 3.612 3.606

19 3.64 3.64 3.637 3.633 3.623 3.621 3.618 3.614 3.612 3.610 3.606 3.605 3.602 3.596

43 3.64 3.64 3.636 3.632 3.621 3.619 3.616 3.611 3.610 3.607 3.603 3.603 3.600 3.593

11 3.64 3.64 3.637 3.633 3.623 3.621 3.619 3.614 3.613 3.610 3.606 3.606 3.603 3.596

44 3.64 3.64 3.637 3.632 3.621 3.620 3.617 3.612 3.611 3.608 3.604 3.603 3.600 3.594

8 3.64 3.64 3.637 3.633 3.623 3.621 3.619 3.614 3.612 3.610 3.606 3.606 3.603 3.596

42 3.64 3.64 3.638 3.634 3.625 3.623 3.620 3.615 3.614 3.611 3.608 3.607 3.604 3.598

33 3.64 3.64 3.639 3.636 3.627 3.625 3.623 3.619 3.618 3.615 3.612 3.612 3.609 3.603

27 3.64 3.64 3.639 3.635 3.626 3.625 3.623 3.618 3.618 3.615 3.612 3.612 3.609 3.603

41 3.64 3.64 3.639 3.635 3.626 3.625 3.622 3.618 3.617 3.614 3.611 3.610 3.608 3.602

9 3.64 3.64 3.639 3.636 3.627 3.625 3.623 3.619 3.618 3.616 3.613 3.612 3.610 3.603

21 3.64 3.64 3.639 3.635 3.627 3.625 3.623 3.618 3.618 3.615 3.612 3.611 3.609 3.603

20 3.64 3.64 3.639 3.636 3.627 3.626 3.624 3.619 3.618 3.616 3.613 3.612 3.609 3.604

 

[TommyHolly]

Ya my friend, you were done a long time ago (days).

Its not internal resistance, its voltage difference that is slowing the process down. At 10mv difference between charger and cells there simply isnt that much current that can flow into one cell. But if you multiply that 0.017a by the 48 cells you are charging you are still seeing 0.816a going into the whole pack.


Sure, but dont hold them there until 0 current. As said above, personally, Id stop when current hits 5 amps? maybe 2. In truth, you are "top balanced" well before you get to 3.65 volts (Like at 3.60).

Good to know. They are currently resting at 3.654v after discharging them from the dangerous 4.32v I found them at this morning. I got them down to 3.621v but after removing the load they went back up. I kept putting the load back on until they wouldn’t go back up over 3.65v and they still went up a little bit over.

I’ll just let them sit there for now and they should go down over the next day or so from normal internal resistance.

 

[noenegdod]

They don’t settle at 3.64v
They continually drop at a steady rate.

Once fully charged, they will "settle" down to something like 3.4V (depends on the cells), but are still fully charged. It isn't because of the internal resistance. The self-discharge of something like 1-2% per month is due to internal resistance.

3.4. Not 3.64

 

[TommyHolly]

No…
I would connect the parallel set, and arrange your BMS connect to load, and put them in service.
I would NOT charge them back to 3.65

Hey all made it up to full, and they all dropped to 3.55 which is a fine top balanced goal.
Just assemble them and get them working.

Ok, I have an appointment for Wednesday to have an electrician come help me assemble my LiFePo4 cells back into my system. For now I’m letting these cells sit there where they currently are. 3.654v

After I wrote this original post, I was able to get them down to 3.231v and they actually went back up to 3.71v after removing the load and letting them sit for an hour. So I’ve been checking on the occasionally and anytime they get too high by themselves, I put the load back on to lower them. I’ve needed to do that less and less and they seem to be resting at 3.654v without moving.

 

[TommyHolly]

3.4. Not 3.64

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