Li-ion retirement?

[PaleAle]

Hi

Got here an older 18650 pack 3s4p.

When ballance charging the it does not get past 88%

S1 = 4.00v
S2 = 4.01v
S3 = 4.20v

Got a few options now: retire, use or open up pack and find the bad cells
to replace them (I got in fact 2 packs with simular issues so a could merge them)

My charger can show the resistance but i'm not sure if there is any point in doing
that, doesn't 1/Rv apply here?)
Anyway the results are 35 mOhm 19 mOhm and 25 mOhm .


But my question, better to retire the pack or use it a few more times?

 

[jonyjoe303]

Something you can do is get active balancers and continue to use the pack that way. I been using a 220ah 4s lifepo4 for almost 5 years with active balancers. Without the active balancers 1 cell was always full before the other 3 cells, with the active balancers they reach full at the same time. This is a picture of the active balancers I been using, these cost my 100 dollars, these are great for larger batteries.


But for a smaller battery you can use the cheaper balancers like these which are in the 25 dollar range. On youtube there are people who review the active balancers to see which ones actually work.

 

[docw009]

You said you're already using a balance charger and two banks are stuck at 4V? I would blame tired cells in those banks. If you like doing this kind of stuff, take it apart, test each 18650 separately and pullout the bad ones. On the other hand, twelve new cells aren't that expensive.

 

[jonyjoe303]

Some balance chargers will balance at too slow rate. I had an ISDT balance charger that balanced at 1 amp and it wouldn't balance my 220ah lifepo4, it would keep shutting down. I also tried the balance charger on a smaller 3s10p li-ion battery that was out of balance and it would also shut down. Balance charger only seems to work if the balance isn't too far off.
When the cells get too far off in balancing, they need to be brought back into balance with active balancers or with a balance charger (if you can get it to work) or take the battery apart and replace the weak cells.
In my situation my 220ah battery is made up of 160 cells, for me it was too much work to take it apart and check every cell. The active balancers allowed me to keep using the battery.

 

[PaleAle]

Ok, will take them apart , balancing is not working... it has been trying for more than 1.5 hr.
still the same voltages.

Then I can also check the resistances per cel. Luckily for me there are only 12 cells..

tnx for all the sugestions...

 

[Hillhater]

Before spliting the packs,..try “manual” ballancing of the groups by boosting the low voltage groups up to match the higher voltage groups, using a single cell charger. ( or drop the higher voltage cells back to match the others)
Then cycle them a few times to see if they still lose balance.
it would not be the first time that the BMS has been the cause of an unballanced, pack rather than the actual cells.
…? But 88% pack capacity is not exactly a huge problem !

 

[calab]

Balance charger only seems to work if the balance isn't too far off.

Otherwise it takes forever.

What is the charger the original post has?