3.2V LFP module went up to over 270V

DeValency

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A strange issue. Built two 100A 4S LFP batteries. Each had a separate and different BMS. Both worked well on a bench for months without any discharge after a proper charge within the levels for each module and battery.

Few months later, after being disconnected from the chargers checked each module again and one was showing a strange 270V (now dropped to 241V)! The other three were just fine at 3.2-3.3V.

Happened with each 4S battery. One module in each, each had a different BMS, different charger and the batteries were not connected

Can anyone here explain this? Can it be repaired?
975C0836-79C2-40C0-AE83-93B98761957B.jpeg
 

DeValency

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That's 241mV, in other words 0.241V. You discharged them too far, or they were dead to begin with.
ooops. Thanks. You are right... :) but never discharged as explained below, they were all fine for few months and apparently one module died, the other three stayed at their nominal voltage...
 

upnorthandpersonal

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And the BMS didn't shut the battery down because that cell went low?

Edit: these are LiitoKala cells - there have been more than a few complaints about those; search the forum.
 

DeValency

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And the BMS didn't shut the battery down because that cell went low?

Edit: these are LiitoKala cells - there have been more than a few complaints about those; search the forum.
The BMS shut down the entire battery at some point, I didn’t check the battery for months as it was disconnected. Apparently this module continued to drop… Thanks for the info on this seller!
 

meetyg

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Seems like a bad cell, or maybe just not balanced.
I would try to slowly charge that one cell up, using a PSU at 2.5v, and no more than say 200-300ma.
When it reaches 2.5v, let it sit for a few (2-3) hours, see if it holds the charge. If it does, then charge it up to 3.4v, no more than 5A current.
Then again let it sit for a few hours, see if it stays above 3.35v. If so, you should connect all 4 cells in parallel and do a proper top balance.

Then put together your 4S setup, and do a slow discharge test, watching the BMS and cell voltages, to see if it's acting OK.
If not, check your connections, bus bars, balance leads etc...

If all is well but still the cell drops down to fast, it's probably a bad or weak cell, have it replaced.
 

DeValency

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Seems like a bad cell, or maybe just not balanced.
I would try to slowly charge that one cell up, using a PSU at 2.5v, and no more than say 200-300ma.
When it reaches 2.5v, let it sit for a few (2-3) hours, see if it holds the charge. If it does, then charge it up to 3.4v, no more than 5A current.
Then again let it sit for a few hours, see if it stays above 3.35v. If so, you should connect all 4 cells in parallel and do a proper top balance.

Then put together your 4S setup, and do a slow discharge test, watching the BMS and cell voltages, to see if it's acting OK.
If not, check your connections, bus bars, balance leads etc...

If all is well but still the cell drops down to fast, it's probably a bad or weak cell, have it replaced.
Many thanks for the detailed possible repair receipt! This is very helpful. As the cell (module) is of 100A capacity it could take a long time to reach 2.5V @ 200-300mA… no? But that’s ok. The battery was sitting here for about 8 months so could wait few more…
So far LitoKala are not even responding nor even acknowledging receipt of the message.

Thanks again!
 

meetyg

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Many thanks for the detailed possible repair receipt! This is very helpful. As the cell (module) is of 100A capacity it could take a long time to reach 2.5V @ 200-300mA… no? But that’s ok. The battery was sitting here for about 8 months so could wait few more…
So far LitoKala are not even responding nor even acknowledging receipt of the message.

Thanks again!
Because there is a high voltage difference and because there is hardly any charge below 2.5v, it should go up to 2.5v fairly quickly. After that it will take longer, yes.
But as far as I know, this is the safest way to bring back a "dead" cell to life without damaging it. Maybe I'm not exact about the numbers, but in general a very slow and low current charge is needed below 2.5v.
 

DeValency

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Seems like a bad cell, or maybe just not balanced.
Thanks again! I was able to recharge the cell to the rated voltage of 3.3V, it took three days.

Here is somewhat related question. I can see all the dedicated LFP 4S chargers are 14.4V and these are the charging voltages I see all around. However, if the four cells are well balanced at 3.3-3.35V, which is over 90% fully charged, the charging voltage can be 13.2-13.4V - correct? So why the standard chargers are of 14.4V?

Now, I have noticed that the Daly (and other) BMS, have the internal passive balancer and when checking simultaneously the cells voltage during charge and quite a long time after disconnecting the charge, they hardly been balanced and keep differences of over 20-30mV, and indeed the charge is maintained at higher voltage as I guess the BMS refers to the lowest cell voltage, while at the same time start to overcharge the highest cell (I have seen 3.75V). So I installed a small active balancer that can transfer up to 5A and the balancing turns perfect at no more than 8mV...

So went and preset a Victron programmable charger to max 13.5V and it looks like the battery is happy where are the cells are actively balanced while charging, it complete the charge very fast without any spikes at any of the cells. I have not yet checked the discharge capacity, but based on the cells parameters, I would hope to get the rated power.

Comments? - Many thanks!
 
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