Jk bms balancing issues

[GuyS]

How many amp hours or kwh did you get out of the battery when you saw the 0.5v difference?

I turned the battery off when I spotted it. At that point it was 280ah out of 320ah

 

[TimE]

Looking at your first image. You have an average cell voltage of less than 3.0v. Why are you balancing at these voltages? You don't want the balancer activating until 3.4v as a minimum. You can see the balancer is working in the image. You need to sort this out as you are not top balancing with this set up

 

[JJJJ]

I would try cleaning my bus bars. 3m light buff and alcohol wipe and dry. Double check torque settings with supplier. I like to go shy of permitted for safety.

Since different cells are responding the same and no significant difference in wire resistance that would be the first thing I would check.

 

[GuyS]

Looking at your first image. You have an average cell voltage of less than 3.0v. Why are you balancing at these voltages? You don't want the balancer activating until 3.4v as a minimum. You can see the balancer is working in the image. You need to sort this out as you are not top balancing with this set up

I'm not usually I only turned it on to bring that one back in line on this one occasion as the differences were large and I was worried it would damage the battery. I did a full top balance the day after this and turned balancer back to 4.5v.
First cycle after this it did the same thing

 

[RCinFLA]

The screen shot you posted shows zero current on battery. If it has been at zero current for a few minutes then it represents equilibrium open current voltage on cells.

That says the cells are mostly totally discharged with the 3.07v, highest voltage, cell having about 3% capacity remaining, while 2.6v, lowest voltage cell is about 1% capacity remaining.

Cells are likely just not perfectly matched for capacity. For example, if highest capacity cell was 315 AH and lowest capacity cell was 307 AH.

New 304 AH cells typically range from 304-320 AH initially, so if not specifically selected for matching AH's, the variance you are seeing is not out of the ordinary.

Realize running cells regularly from totally full to totally empty will stress the graphite negative anode due to graphite's 11% volume expansion between totally empty to totally fully charged. This will reduce cycle life of cells.

 

[TimE]

I'm not usually I only turned it on to bring that one back in line on this one occasion as the differences were large and I was worried it would damage the battery. I did a full top balance the day after this and turned balancer back to 4.5v.
First cycle after this it did the same thing

You can't get it 'back in line' with the balancer below 3.4v. At the top of the charge it will be out of balance regardless. Have you tried leaving the battery in absorbtion for an hour at 3.55v per cell with the balancer running?

 

[GuyS]

The screen shot you posted shows zero current on battery. If it has been at zero current for a few minutes then it represents equilibrium open current voltage on cells.

That says the cells are mostly totally discharged with the 3.07v, highest voltage, cell having about 3% capacity remaining, while 2.6v, lowest voltage cell is about 1% capacity remaining.

Cells are likely just not perfectly matched for capacity. For example, if highest capacity cell was 315 AH and lowest capacity cell was 307 AH.

New 304 AH cells typically range from 304-320 AH initially, so if not specifically selected for matching AH's, the variance you are seeing is not out of the ordinary.

Realize running cells regularly from totally full to totally empty will stress the graphite negative anode due to graphite's 11% volume expansion between totally empty to totally fully charged. This will reduce cycle life of cells.

So you wouldn't worry about 0.5v difference between cells? Bms says its pulled 280ah at this stage from a 320ah battery. Unless the cells I received were actually 280 and not 320?
I have set the inverter to stop discharging at 10% but it does seem to be going to 0% on the bms and my shunt.

 

[GuyS]

You can't get it 'back in line' with the balancer below 3.4v. At the top of the charge it will be out of balance regardless. Have you tried leaving the battery in absorbtion for an hour at 3.55v per cell with the balancer running?

I did a top balance with all cells getting to 3.63v using a power pack, rebuilt and plugged into bms, shunt and inverter and within minutes voltage dropped to 3.42v across the board, all within 0.05v. When plugged into the inverter the voltages never seem to get above 3.43v (even if I charge for days none stop)
Unless my inexperience is raising unnecessary alarm bells, but something just doesn't feel right

 

[TimE]

So you wouldn't worry about 0.5v difference between cells? Bms says its pulled 280ah at this stage from a 320ah battery. Unless the cells I received were actually 280 and not 320?
I have set the inverter to stop discharging at 10% but it does seem to be going to 0% on the bms and my shunt.

I did a top balance with all cells getting to 3.63v using a power pack, rebuilt and plugged into bms, shunt and inverter and within minutes voltage dropped to 3.42v across the board, all within 0.05v. When plugged into the inverter the voltages never seem to get above 3.43v (even if I charge for days none stop)
Unless my inexperience is raising unnecessary alarm bells, but something just doesn't feel right

There is more to this problem than a cell balancing issue.

 

[Checkthisout]

You have how many connections on cell 16?

 

[Berseker]

Strange case.
Try setting the cell cutoff/lvd voltage to 3v x nos of cells and upper cutoff/hvd to 3.45v x nos of cells on ur inverter.
Then set same on bms 2.9v and 3.5v.
Set balance trigger delta to be 0.02v and start voltage 3.3v

 

[740GLE]

Why set the trigger so high? 20mv? Did you mean .002v

Lowest I could get my 8s set to is .003v.

 

[Berseker]

Why set the trigger so high? 20mv? Did you mean .002v

Lowest I could get my 8s set to is .003v.

Since the trigger voltage is low, a high delta ensures balancing only happens when necessary.
User can set 0.01v instead

 

[scott harris]

The UK has a relatively damp atmosphere, even inside metals oxidise. So to be 100% sure of the connection use the 3M on both contact surfaces even if the battery has never been outside.

What is 3m cloth?

 

[hogback]

Emery cloth - cloth-like sandpaper.