Top Balance - JKBMS - drift voltage between pair and odd cells

Andre Magro

New Member
Joined
Jun 16, 2020
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30
What was your charge voltage?
I would say put the pack into service and see if the BMS can keep the cells top balanced.

Ok, so I will let them settle down, and give the final charge of 3.65*8 in series.
Can I assume after that, that they are top balanced?
 

RCinFLA

Photon Sorcerer
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Jun 21, 2020
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1,696
One thing I saw and forgot to mention.

Change the setup for start of balancing. You presently have it set to 3.0v. Change it to 3.4v.

Balancing in the flat portion of discharge curve will likely misbalance cells so you have a cell overvoltage shutdown problem when attempting a full charge absorb cycle

When you have a moderate amount of inverter discharge current, slight cell impedance variations and variation in battery terminals connection resistance will cause more or less voltage drop, enough to send the balancer balancing in the wrong direction.

Somewhere in the setup screens there is a balance variance setup. No benefit to set it any lower than 5 millivolts as that is about the real accuracy of BMS cell voltage determination. Setting it lower just causes balancing to thrash on and off more.
 
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time2roll

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Mar 20, 2021
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3,599
What is the expected in service charging voltage?
Time for the mad scientist part to end and put these cells to work.
 

Andre Magro

New Member
Joined
Jun 16, 2020
Messages
30
One thing I saw and forgot to mention.

Change the setup for start of balancing. You presently have it set to 3.0v. Change it to 3.4v.

Balancing in the flat portion of discharge curve will likely misbalance cells so you have a cell overvoltage shutdown problem when attempting a full charge absorb cycle

When you have a moderate amount of inverter discharge current, slight cell impedance variations and variation in battery terminals connection resistance will cause more or less voltage drop, enough to send the balancer balancing in the wrong direction.

Somewhere in the setup screens there is a balance variance setup. No benefit to set it any lower than 5 millivolts as that is about the real accuracy of BMS cell voltage determination. Setting it lower just causes balancing to thrash on and off more.
I followed the previous advice of @smoothJoey and already change to 3.425.
 

Andre Magro

New Member
Joined
Jun 16, 2020
Messages
30
Time for the mad scientist part to end and put these cells to work.
As a newbie I'm just following the experts advices: top balancing + capacity test before putting the cells at work.
I have more 8 cells to top balance, and then I will do a full 16 cell capacity test.
 

740GLE

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Apr 30, 2021
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1,095
I’d say top balance in parallel if you want but I’d almost say the BMS is doing its job and put it in service.

Proper top balance may get you another what 2% capacity? But the BMS should get you there after the first dozen cycles or so.
 

pierre

Somewhere down South
Joined
Dec 21, 2019
Messages
903
Time to cycle your battery a few times to test your efforts and then throw a Heltec 5A balancer into the mix.
I think we fuss too much about balancing to the last mV. Cell delta under 50mV is quite acceptable.
Purists , shoot me now.
 
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