Battery fellas are dying early

[lifeisajarnie]

We have a 48V system with 16 cells in series and an Overkill BMS. For some reason, we have cells that die earlier than the other cells.
Cell 2,4,11,12 seem to hold less charge. Screenshots of 100% and 0%.
Not sure if there is a balancing issue or if cells need to be replaced.

 

[lifeisajarnie]

Current settings

 

[Drunkin Solar]

That looks wildly out of balance.
Your balance start configuration is wrong and needs to be set at least 3400mv.
Try reducing your charge voltage in absorption to 56v and hold it there. Check to see if balancing is occurring after reaching 3400mv per cell.
It will take time but I think eventually you should be able to get that pack straightened out. And then readjust your settings later.

 

[mikefitz]

some reason, we have cells that die earlier than the other cells

Did you carry out a top balance before building the battery?
The ballancer configuration in the BMS need changing, set 'start balance ' to 3400mV, set 'delta to balance', to 30mV.
Many ofthe protection values are wrong and may have caused damage. Did you receive the BMS with these values?
Cell min volts at 1400mV is not good, as is charging down to -10C.

 

[ScrodusGargleRotten]

Someone please start the popcorn. We going to be here for a bit.

 

[42OhmsPA]

Take it all apart and top balance it properly or buy a high amperage active balancer and add it.

Increase cell under voltage to 2.5V minimum.
Increase charge under temp to 0C minimum.

Post photos of the build.

 

[ScrodusGargleRotten]

We have a 48V system with 16 cells in series and an Overkill BMS. For some reason, we have cells that die earlier than the other cells.
Cell 2,4,11,12 seem to hold less charge. Screenshots of 100% and 0%.
Not sure if there is a balancing issue or if cells need to be replaced.

Cells 1,3,5, and 7 are your problem. These cells are prohibiting the rest from charging.

 

[OzSolar]

Battery Fellas? I'll show myself out.

 

[ScrodusGargleRotten]

Battery Fellas? I'll show myself out.


View attachment 279273

Did you hear they are dying early?

 

[OzSolar]

Did you hear they are dying early?

It's a dangerous lifestyle.

 

[lifeisajarnie]

Initially when the pack was assembled it was top balanced but it’s been a while. I implemented the changes you guys were talking about and I think it’s way better.

 

[ScrodusGargleRotten]

Initially when the pack was assembled it was top balanced but it’s been a while. I implemented the changes you guys were talking about and I think it’s way better.

Whatever you were doing, you are only about half done. The gaps will be much greater at 3.48v

 

[yabert]

I think it’s way better.

No. Cells at 3.21V are at the bottom of SOC and other cells are a bit over 50% SOC.
You have to bring all cells at 3.4V and over to have a balanced battery.

 

[lifeisajarnie]

Is there a way to do that without disassembling the pack? I think cell 1 keeps hitting the max threshold for voltage. Is it also possible certain cells are degraded?

 

[740GLE]

where did you buy the cells?

And did you check the BMS cell voltage readings against an actual meter to verify actual cell voltages?

 

[42OhmsPA]

Is there a way to do that without disassembling the pack? I think cell 1 keeps hitting the max threshold for voltage.

Yes, multiple.
Bleed of the high, charge up the low, add an active balancer are all options.

Is it also possible certain cells are degraded?

Do the same cells hit empty and full first?

 

[lifeisajarnie]

where did you buy the cells?

And did you check the BMS cell voltage readings against an actual meter to verify actual cell voltages?

Chinese reseller, pack was verified when we assembled it but prob need to check again

 

[lifeisajarnie]

Yes, multiple.
Bleed of the high, charge up the low, add an active balancer are all options.

Do the same cells hit empty and full first?

What the best way to bleed or charge those? Any recommendation for active balancer?

Yes, consistently 1,3,5 are hitting the top of the range and 2,4,11,12 are dying early.

 

[42OhmsPA]

What the best way to bleed or charge those? Any recommendation for active balancer?

Yes, consistently 1,3,5 are hitting the top of the range and 2,4,11,12 are dying early.

Resistors would work to bleed them, so would an incandescent light bulb.
Bench power supply for charging.
Active balancers I see mentioned here often are Enerkey, Neey, Heltec.

I suspecting they aren't degraded since the same cells aren't hitting full and empty first.

 

[ScrodusGargleRotten]

I suspecting they aren't degraded since the same cells aren't hitting full and empty first.

This is key. My thoughts exactly.

A terrible cell would be first to charge to 100 AND first to be at 0

 

[Frick]

This is key. My thoughts exactly.

A terrible cell would be first to charge to 100 AND first to be at 0

I had exactly this happening on one cell, shut it all down to swap it with my spare, turned out it was a single loose bus bar nut. It is a 24v 8s2p, and my number 8 pair was not so much connected well with its partner. Just fixed it today and everything is slowly balancing back to normal. I had it quit at 40% charge with cell 8 hitting under volt shut off and also hitting over volt spikes at end of charge before the others were totally full,

 

[lifeisajarnie]

Thanks for the help all, think it’s finally good to go!

 

[740GLE]

I’d call that good enough to not worry about it.

 

[ScrodusGargleRotten]

Thanks for the help all, think it’s finally good to go!

What did you eventually do? and for how long?

 

[lifeisajarnie]

What did you eventually do? and for how long?

Tried the manual strategy, was taking a while. So I just installed a EnerKey active balancer and charged up the pack slowly. It worked like a charm