Problem with 280Ah pack - did I toast these batteries?

[400bird]

2. take them mostly apart (by removing the BMS)

I think you need to look at your BMS and settings, it should never have allowed that cell to reach 3.97 volts.

 

[time2roll]

If the active balancer is added the rest is probably redundant. At some point need to accept it is what it is.

 

[Corbury]

For many installs, when the batteries won't be used for months at a time, everything gets disconnected from the battery. That would include both the BMS and any active balancer.

Interesting. I was hoping that these battery modules would be pretty much like an SOK or similar - no need to disassemble when storing.

I think you need to look at your BMS and settings, it should never have allowed that cell to reach 3.97 volts.

I posted the settings at the start of this thread - cell overvoltage trigger setting is 3650mV and cell full voltage is 3400mV. I think these are the right settings?

 

[HRTKD]

Interesting. I was hoping that these battery modules would be pretty much like an SOK or similar - no need to disassemble when storing.

A BMS that isn't doing anything doesn't draw much and could be kept in place. I'm talking specifically about the Overkill Solar (JBD) BMS. There were numbers published that showed that it doesn't draw much. If you have an active balancer, I have no experience with that.

 

[Corbury]

If the active balancer is added the rest is probably redundant. At some point need to accept it is what it is.

it this what I'm looking for? I'm just concerned this is too small?

 

[Fpoet]

When I reassembled my packs last month (mainly to replace the busbars), I decided to skip the step of reconnecting the cells in parallel to top balance, and do this operation solely with the active balancers. I was able to bring all the cells between 3.60 and 3.65 volts, using the Xiaoxing app (I have JBD BMS's) to interrupt and restart the charging.

- connect the active balancers (my Heltec are externally mounted, so I can manually disconnect them)
- turn off BMS balancing
- connect a low amp charger (I use a NOCO 10 A charger)
- monitor the charging closely using the app
- when one cell reaches 3.60 or so, stop the charging using the app
- let the active balancer work for some time
- when the gap between cells has decreased some, restart the charging from the app
- repeat until all cells are between 3.60 and 3.65V.

I am happy with how the cells stayed together since then, even when using the induction cooktop (about 135A discharge, 65A per battery).

It may not be the best to sollicitate the BMS like this, but this is the most convient way for me to rebalance without having to take the batteries out of the vehicle. I assume that with a very low charge rate, intervention using the BMS to stop and restart charging would be minimal.

I now disconnected the active balancers and reactivated BMS balancing. I will see how the BMS alone can keep the cells balanced.

 

[Fpoet]

it this what I'm looking for? I'm just concerned this is too small?

This is indeed what I have been using.

I mounted them externally to my battery cases to have the possibility of connecting and disconnecting them if need be. There is a way to add a switch, but you need some PCB soldering skills to do it. (I did try and actually ruined one balancer...)

 

[time2roll]

it this what I'm looking for? I'm just concerned this is too small?

Have one on each of my batteries. Never did a top balance. Works good.

Are the cells perfectly in balance at 3.600 volts? No. However my regular charge to 3.45vpc is within 8 mv.

 

[llubi]

You put the cells in parallel and top balanced to 3.65v and then seperated the cells and 1 cell is still higher than the rest?

Yes, I put them in parallel, charged to 3.65 (max according to spec sheet) to make the 3 lower voltage cells go to the highest cell. Then get they at 3,65 for 2 hours. As I wanted to see if the highest cell was broken, I then disconnected the parallels and measure every 3 hours the voltage without loads. The highest one is not moving from 3,62v (36 hours resting) when the others are at 3,49v.

When in use, I get not a real BMS, just 2 Victron battery protects and a Healtec 4S active balancer that I connected manually every month for 3 days and a ISDT BG-8S to check voltages and make minor balancing.
Every time I checked cells were around 5-10mv at any SOC, but from this Saturday is as high as 500mv, and I’m worried because of that.

Thanks!

 

[llubi]

I don't think there is much that can be done except to replace cells. What happens at the low end when deeply discharged?
Consider an active balancer as these cells may need more balancing than the BMS can provide.

I want to wait some days to see if they stop in a rest voltage and then will do the deep discharge test. Just did once and according to what I wrote delta was 50mv.
Would you change the highest cell or the 3 lowers?
Thanks!

 

[llubi]

Ok

At that state of charge is only takes a few amp hours.
try using a resistor to lower the high cell to the same as others or if one is low use
a lap power supply to bring it up the others
When above 3.4 volts very small changes in charges make a large difference in voltage.
At 3.5 volts it is even smaller.
I get mine to be close at 3.45 and leave it be. The amount of amp hours difference is in the low single digits when about 3.45

Ok, so charging just to 3,45 and see if they 4 charge equal?
Thanks!

 

[time2roll]

I want to wait some days to see if they stop in a rest voltage and then will do the deep discharge test. Just did once and according to what I wrote delta was 50mv.
Would you change the highest cell or the 3 lowers?
Thanks!

If the high cell is also the low cell then it would seem to indicate diminished capacity and subject to replacement.

 

[400bird]

I posted the settings at the start of this thread - cell overvoltage trigger setting is 3650mV and cell full voltage is 3400mV. I think these are the right settings?

Those settings look fine, but if your BMS was working it should have disconnected long before your cell reached 3.97 volts.

 

[Corbury]

Those settings look fine, but if your BMS was working it should have disconnected long before your cell reached 3.97 volts.

I know - that's what's worrying me. As well - now the BMS is showing 100% at 243Ah - instead of the 271Ah it used to show. This was part of my concern about toasting the batteries. Why did the BMS show this "new" and diminished max capacity - when I did not change any BMS settings?

 

[400bird]

I'd recommend either testing the BMS, to verify the low/high cell voltage functions, or throw it away and get a replacement, and test that one.

You could set you max cell voltage to something safe, like 3.3 volts. And your min to something higher, like 3.2 volts. If the BMS doesn't stop the charge/discharge by disconnecting the battery, you've got to figure that out first. The BMS's #1 job is to protect the cells from things like over voltage.

 

[Fpoet]

Those settings look fine, but if your BMS was working it should have disconnected long before your cell reached 3.97 volts.

I know - that's what's worrying me. As well - now the BMS is showing 100% at 243Ah - instead of the 271Ah it used to show. This was part of my concern about toasting the batteries. Why did the BMS show this "new" and diminished max capacity - when I did not change any BMS settings?

Corbury, did one of your cells actually reach 3.97 volts? I do not see you mentioning that in the thread.

 

[DonPhillipe]

This is indeed what I have been using.

Just finished almost an identical setup, 2 x 280 for redundancy and the JBD units and I left the settings default while my initial test bank (4S) charged up to around around 3.43 volts and then as the SOC was approaching in the high 90% range one of the cells headed for 3.55 and the JBD went into a cycle mode of up/down. Otherwise in my case, it's the microwave (165A) that saddles them with the rest of the time a small load.

I just finished installing all this 2 days ago for testing.

Did you change the default settings on your BMS and where did you find the values? Thanks!

*** Have added a Heltek 5A balancer to see if it helps out or not. Will have to wait for the freezing weather to change before testing continues.

 

[Corbury]

Corbury, did one of your cells actually reach 3.97 volts? I do not see you mentioning that in the thread.

Good point - to my knowledge - the answer is NO. Max I can see from my screenshots is 3.616. Maybe the 3.97 is from another poster?

But coming back to the max capacity for the battery - has anyone seen the BMS (overkill solar) "reset" capacity to a lower number - by itself?

thanks, C

 

[MisterSandals]

But coming back to the max capacity for the battery - has anyone seen the BMS (overkill solar) "reset" capacity to a lower number - by itself?

How many charge cycles since the reset?
You screenshots showed just a couple; from what i recall 2 and 5 charge cycles. These would be my guess at minimal cycles to start getting good capacity and SoC numbers.
FWIW, while i have Overkill BMSs (2 in continuous use), i do not pay attention to these numbers. I think the BMSs safety features are what they are build/designed for and the capacity/SoC calculations are VERY rough, at best.

 

[Corbury]

How many charge cycles since the reset?
You screenshots showed just a couple; from what i recall 2 and 5 charge cycles. These would be my guess at minimal cycles to start getting good capacity and SoC numbers.
FWIW, while i have Overkill BMSs (2 in continuous use), i do not pay attention to these numbers. I think the BMSs safety features are what they are build/designed for and the capacity/SoC calculations are VERY rough, at best.

Thank you! Interesting - so I also have a Victron BMV - battery monitor - I was thinking that the BMV indication was less accurate than the BMS - but maybe I'm wrong?

BTW - full charge cycles are very low - like 5-7 cycles - these batteries are basically brand new.