10s3p LGABHE41865 with 1 low parallel set

[d3drturner]

I have a battery of 10s3p LGABHE41865 2500mAh 20A.
Cells come from a 60v Greenworks lawnmower that was used one time and failed to charge after that.
Suspecting a bad BMS I took the battery apart and tested each cell which tested nearly identically.
I re-welded these for 36v 10s3p using BMS SP15SV0001-LLT from lithiumbatterypcb.com
Used lightly for a couple years in my grocery getter.
Parallel set 2 is lagging behind the others; at full charge it shows 3.9 vs 4.2 for the others
I thought I might replace the #2 set with 3 new LGABHE41865
However, I can't find them for sale anywhere.
What should I do about this? Junk the whole battery? Use some other equivalent cells to replace the low set?
Is this BMS failing to balance the #2 set?

 

[docw009]

I'm not going to look up your SP15SV0001-LLT BMS., but I do see that some of the 10S units sold by your BMS vendor aren't balance BMS. It may depend on whether you have a balance BMS. If you do, it means your low group is no good.

I would expect a balance BMS to be able to equalize the pack, even with one group using new cells. Another set of 2500 mah cells would probably work. The battery will probably need a balance charge on every charge though. The new group will probably recharge first, and then the BMS will bleed it while the other nine groups catch up. That could take a while. And since we can't model it, you won't know how long it takes til you try it.

The other complication is how long will the other 27 cells last? I don't think it's worth it, unless you have the time to spend on this experiment.

.

 

[d3drturner]

Hi,
This has been going on for a while.

On Apr of 2023 I asked the vendor about the seeming lack of balancing.
Q: "I have 9 sets at 3.99 and 1 at 3.94; why does it not balance"
A: "Hi , as 3.94V , the difference was not big , it does not matter actually"

Then on Aug 2023
Q: "diff is 3.8 vs 4.0; why does it not balance?"
A: "Hi , as for this case , the voltage difference are too big , whats the real voltage of number 2 cell
BMS balance performance will not work ideally if the difference are too big
you can use other methods to balance your battery without problems , such as active balance module"

At which point I asked if it doesn't balance when the difference is too small or too big, when does it balance?

A: "if the voltage difference are too big , the balance function will not work as well, it is passive balance with 30mA ~40mA balance current"

I'm not clear if the "balance" part does any balancing. I did manually balance a couple of times and it seems clear there is something wrong with one or more cells in that group 2. I can get them even with the others but they revert to lagging within a few uses.

"The other complication is how long will the other 27 cells last? I don't think it's worth it, unless you have the time to spend on this experiment."

The other 27 cells probably are good for many years. My guess is that it has less than 50 complete cycles worth of charging. I have only used this battery for short rides and keep the charge level between 30 and 80% in the normal course of usage. I have time as it's not my primary transport and I also have another battery for it. I'm treating it as a learning experience.

Thanks for your input. Scouting around for reliable vendors of BMS and 18650 cells. Is there a list of vetted vendors somewhere?

 

[docw009]

In the US. the two cell vendors I have used are liionwholesale.com and 18650batterystore.com. I consider both reliable.

A US BMS source is srikobatteries.com which has a chicago shipping center and sells both cells and BMS. I bought a pair of Daly BMS from them, but haven't used them.

My overall BMS results have been mixed/problematic, I chalk it up to problematic vendors and also bad handling on my end. Static discharge damage is quite real, and I'm too lax on my part.

 

[d3drturner]

Thanks, I will probably get 3 Samsung 25R 18650 2500mAh 20A Battery for $10 + $10 shipping. I actually have a jiabaida BMS that I went to all the trouble to connect just to test whether the other BMS was defective. Behavior was the same. I know about static; killed a Bosch powertube 625 with it. One zap when plugging in the charging cable and that $1000 battery was toast.