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

[smoothJoey]

Wonder why the cell delta shows as 0.

 

[Andre Magro]

Wonder why the cell delta shows as 0.

I think is related in the screen of my mobile phone, the delta value have 3 decimals, on my screen only shows 2 of them.

 

[Andre Magro]

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?

 

[upnorthandpersonal]

It's all good - take the pack into service. You also don't have to charge that high anymore: 3.45V or 3.5V per cell (27.6V to 28V) is fine.

 

[smoothJoey]

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?

Why?
They are as top balanced as they are going to get.
I suggested to put them in service so we can see if the BMS can maintain the top balance.

 

[RCinFLA]

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.

 

[time2roll]

What is the expected in service charging voltage?
Time for the mad scientist part to end and put these cells to work.

 

[Andre Magro]

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]

What is the expected in service charging voltage?

Sorry, but I don't understand this question?
The voltage of the inverter to charge the batterie, is that?

 

[Andre Magro]

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]

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]

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.

 

[Niz76]

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.

100% agree