Please help balance pack (batrium auto level for a long time)

[m1kkel]

Hi there

I’m trying to get my pack’s in balance. I have 3 or 4 cells that never reach same voltage level as the rest. It’s a difference on 0.12 volt.

I’m using batrium bums with Watchmon core and cellmon k9.

Its two new batteries build with eve 280 cells in a 16s configuration. So it’s 16s in two packs hence 32 cells total.

Pack 2 was too balanced for a really long
Time before being out into service, however from the time the battery was build, until it got into service 2 weeks went by, and apparently that’s enough for the cells to drift.

Batrium auto level is working it’s magic but not enough. I don’t quite understand the auto level function enough, so I hope someone here can help.

 

[m1kkel]

Stats.

 

[Zwy]

Hi there

I’m trying to get my pack’s in balance. I have 3 or 4 cells that never reach same voltage level as the rest. It’s a difference on 0.12 volt.

I’m using batrium bums with Watchmon core and cellmon k9.

Its two new batteries build with eve 280 cells in a 16s configuration. So it’s 16s in two packs hence 32 cells total.

Pack 2 was too balanced for a really long
Time before being out into service, however from the time the battery was build, until it got into service 2 weeks went by, and apparently that’s enough for the cells to drift.

Batrium auto level is working it’s magic but not enough. I don’t quite understand the auto level function enough, so I hope someone here can help.

I turned auto level off as it would attempt to bypass cells that didn't really need bypass to occur. It would continually take any cell that was at the Bypass Volt setting and discharge it with bypass. All that did was generate heat at the K9 without any real bypass occuring. The current flowing in by the SCC would be just changed to heat and cells never would get into balance.

Next, I increased bulk charging voltage. You have 3.45V for Bypass Volt so 3.45V x 16= 55.2V which is where the battery currently shows 100% SOC. This will not get cells in balance as the charge controller just sees the pack voltage and stops any real charging. What needs to occur is pack voltage needs to be slightly higher to force bypass to continue to occur bringing higher voltage cells down while the lower voltage cells slowly creep up.

I would increase charging voltage by 0.5V and limit the amps charged to about 20A. Run up to 90% SOC, set charging amps lower to 20A and increase the charging voltage including bulk by 0.5V. I have used 0.25V in float when cells are close to balance. This means that with 3.45V for Bypass Volt, the float should be 55.5V and bulk at 56.0V for 0.25V and for 0.5V it should be float of 56.0V and 56.5V for bulk.

 

[m1kkel]

I turned auto level off as it would attempt to bypass cells that didn't really need bypass to occur. It would continually take any cell that was at the Bypass Volt setting and discharge it with bypass. All that did was generate heat at the K9 without any real bypass occuring. The current flowing in by the SCC would be just changed to heat and cells never would get into balance.

Next, I increased bulk charging voltage. You have 3.45V for Bypass Volt so 3.45V x 16= 55.2V which is where the battery currently shows 100% SOC. This will not get cells in balance as the charge controller just sees the pack voltage and stops any real charging. What needs to occur is pack voltage needs to be slightly higher to force bypass to continue to occur bringing higher voltage cells down while the lower voltage cells slowly creep up.

I would increase charging voltage by 0.5V and limit the amps charged to about 20A. Run up to 90% SOC, set charging amps lower to 20A and increase the charging voltage including bulk by 0.5V. I have used 0.25V in float when cells are close to balance. This means that with 3.45V for Bypass Volt, the float should be 55.5V and bulk at 56.0V for 0.25V and for 0.5V it should be float of 56.0V and 56.5V for bulk.

Thanks for that explanation. But I’m running Victron equipment all over the place, so it’s not possible to define how many amp’s I want to charge with. It’s also not possible to define float, absorption and the other phase. Not as long as im running dvcc enabled and feeding in excess power to the grid.

However I can still try what you suggest, but I can’t guarantee how many amp’s will run into the battery. It’s probably not a lot.

 

[m1kkel]

I turned auto level off as it would attempt to bypass cells that didn't really need bypass to occur. It would continually take any cell that was at the Bypass Volt setting and discharge it with bypass. All that did was generate heat at the K9 without any real bypass occuring. The current flowing in by the SCC would be just changed to heat and cells never would get into balance.

Next, I increased bulk charging voltage. You have 3.45V for Bypass Volt so 3.45V x 16= 55.2V which is where the battery currently shows 100% SOC. This will not get cells in balance as the charge controller just sees the pack voltage and stops any real charging. What needs to occur is pack voltage needs to be slightly higher to force bypass to continue to occur bringing higher voltage cells down while the lower voltage cells slowly creep up.

I would increase charging voltage by 0.5V and limit the amps charged to about 20A. Run up to 90% SOC, set charging amps lower to 20A and increase the charging voltage including bulk by 0.5V. I have used 0.25V in float when cells are close to balance. This means that with 3.45V for Bypass Volt, the float should be 55.5V and bulk at 56.0V for 0.25V and for 0.5V it should be float of 56.0V and 56.5V for bulk.

Also the voltage targets you have defined, aren’t they a little high for Lifepo4 ?

 

[Zwy]

Thanks for that explanation. But I’m running Victron equipment all over the place, so it’s not possible to define how many amp’s I want to charge with. It’s also not possible to define float, absorption and the other phase. Not as long as im running dvcc enabled and feeding in excess power to the grid.

However I can still try what you suggest, but I can’t guarantee how many amp’s will run into the battery. It’s probably not a lot.

Use a separate charger if you have to. Any Victron charger I have allowed me to change charging amps thru the BT app. If you can't adjust amps, then adjust the voltages higher and monitor for any runners. If you can't get balance such as I have described, then you may have to put cells in parallel and top balance to 3.65V. If the cells still won't hold balance, then the cells are questionable.

Also the voltage targets you have defined, aren’t they a little high for Lifepo4 ?

No. Charging voltage should be under 3.65V. You need above 3.4V for effective balancing. Between 3.40V and 3.50V is where balancing should occur, this allows lower cells to move up to 3.4V and above. Once you get above 3.5V, you start to see runner territory.

There will also be voltage drop between the SCC and the battery due to wire resistance. If the SCC is set for 55.2V, the battery may only be receiving 55.0V.

In any case where you want to balance some cells that are considerably out of balance, you should monitor the progress to ensure if a runner does occur, you can keep the cell below 3.65V. This isn't daily cycling, you are trying to get cells in balance. Some will be much higher and some much lower and the SCC only sees the sum of the pack voltage unless you have BMS to SCC communication.

 

[m1kkel]

Hi again

I have had this enabled since July 28th. The strange thing is that your suggestions have helped. Voltage target is 55.3v. However it only helps in the beginning of the end. End in the end, the cells drop again. I think this is really strange. See attached screenshots.