Battery BMS not equal to Victron Smart shunt/Cerbo GX

[Statistical]

Originally Posted by jerrypeters

Thank you all for your feedback and ideas.

I understand voltage is not a reliable indicator of SOC but the difference between 20% and 99% SOC should show a voltage difference of almost 1 volt. Also the solar controllers are behaving normally with respect to voltage and current i.e. the solar controllers "believe" the battery bms SOC as indicated by their response to bulk, absorb and float settings.

The shunt peukert setting is 1.05 and the charge efficiency setting is 99%.

I do not have a BMV-172 installed.

If I had a DC load between the battery and the shunt, the shunt would not show that load and the shunt load would be less than the battery bms load. The opposite is true. I do have a clamp ammeter and I will try to measure against the shunt report. It's not easy to access and I'd prefer to do it without solar input - which is easiest at night. Perhaps I can measure tonight. (Unfortunately the shunt is under one of my guest's bunk )

Do you have a charge source like say solar going "around" the shunt.

There should be nothing as in absolutely nothing wired direct to the battery not going through the shunt. Anything that is well can't be recorded by the shunt.

[Statistical]

Originally Posted by CarinaPDX

The problem is that everyone here is still thinking like FLA batteries. With an FLA battery the current going into the battery during charging is the charge. With these integrated BMS+cells batteries the current going into the batteries is not all reaching the cells. There are at least two or three circuits used by BMS devices so it is hard to say exactly where the power is being lost, but consider this: there are 4 cells in each string, and when one cell in the string is fully charged it must be disconnected from the charge current, while the other cells continue to charge. One solution is to switch a parallel shunt across the charged cell, which of course would convert current to heat. I have to admit that I am no expert, and trying to work out the various BMS circuits is mind-numbing for my old (EE) mind, but suffice it to say that the charging circuits inside the case are taking some of that missing power. Whether there are other explanations I don't know, but I do know that just because it looks like a battery doesn't mean it acts like one when it contains a BMS.
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Greg

The energy consumed by the BMS and the energy "lost" in rebalancing is a rounding error of a rounding error. It is why you might be 0.2% maybe 1% off but not 10%+. If rebalancing lost you 10% of your energy nobody would do it.