Victron Multiplus on JK BMS - Balancing

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Matthias Pallhuber asked Feb 25, '24

Victron Multiplus on JK BMS - Balancing

I am using one of the new inverter JK BMS with 16 x EVE 280 Ah cells. Works fine also due to the support received from Andy@offgridgarage. My settings are as per recommendation of Andy.

One of the observations what I can see is that my cells seem to be drifting apart even that I have balancing activated starting at 3.45 V.

I seem to reach an optimum of balance after 15 minutes of 100% reached.. Its always the same 6 cells which are drifting down in the lower voltage block. Victron tries to stay on 55.2 V so we see one block moving up and one block moving down.

I am wondering why the active balancer is not able to mange that? Any ideas?

BMS

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Answer 1 · 2024-02-25T20:19:40Z

Alex Pescaru answered · Feb 25 at 08:19 PM

Hi @Matthias Pallhuber

Probably a thing that has to do with internal balancing algorithm.

See if it's any change if you try to keep a pack voltage of 56V (3.5/cell) and start balancing from 3.36V per cell?

These voltages are from Pylontech experience/settings.

Alex

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Answer 2 · 2024-02-25T20:20:51Z

thanar answered · Feb 25 at 08:20 PM

Most probably cell voltage measurement error. Every cell voltage is calculated by the BMS based on another voltage value in the battery, heck it could even be the BMS temperature that's playing a role here in deciphering the exact voltage of a cell. You're into too-much micro-management here, imho.

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Answer 3 · 2024-02-25T22:58:54Z

klim8skeptic answered · Feb 25 at 10:58 PM

@Matthias Pallhuber I seem to reach an optimum of balance after 15 minutes of 100% reached.. Its always the same 6 cells which are drifting down in the lower voltage block.

I have 4 winston cells and see the same thing when the charge current bottoms out. I never really looked into this and have just accepted that some cells have slightly different "full" charge voltage. Or perhaps more likely that the active balancer (deligreen) is a bit different at the top cells vs the bottom ones. Cells within 10mV at the start of absorp, going up to within 30mV at the end of absorp at 20 mins, 3% tail current.

Given you have noticed that optimal cell balance is about 15 mins into absorp, and around the same time the charge current bottoms out, it would be safe to suggest that the absorp period can be reduced down to 15-30 minutes.

Additional thoughts. Do check the cell voltages at both the cell and at the balance leads at the BMS.

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