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marekp avatar image
marekp asked

MP-II jumps SOC value from 20% to 100% when 2 signal BMS said "do not charge"

Hi,

My 3 phase system build on 6 x MP-II/3000 uses Lithium battery with BMS that connects to the system through 2 signals (4 wires). One signal is for preventing charging the other discharging.

ESS assistant has "2 signal BMS" selected.

Recently I had a situation when battery was discharged down to 20% and BMS sent the signal "charging not allowed". As a result MP-II set the SOC of the battery to 100% and charging mode to float. In reality, the battery was practically discharged.

The reason the signal was sent, was not that the battery was full (obviously), but temperature of one cell dropped below 5C.

Does anyone have a solution to this problem?

Regards,

Marek

screen-shot-2021-04-24-at-31009-pm.png


bms-tmin-error.jpg

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marekp avatar image marekp commented ·

Hi,

Do anyone have any suggestion how to deal with this problem?

This morning again MP-II set the SOC to 100% but my BMS reports SOC at 17%.

Again minimum battery temperature at 6AM fell below 5C.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

There is an option during the setup of the two-signal-BMS assistant. "Set SOC to 100% if cell is high" or something like that.

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marekp avatar image marekp commented ·

Hi @Matthias Lange - DE,

I do not remember seeing this during the ESS setup.

There is "force to Float when BMS signals battery full...."

This is not saying that the SOC will be set to 100% but maybe "Float" is synonymous to SOC=100%.

But this signal from BMS was not about battery being full but the temperature of the battery was below Tmin=5C.

When I turn of this "force to Float..." option, what will happen when battery will get to full charged state and BMS would send the signal "do not charge"?

Do you know of any other way to get battery's SOC, that would not react to the BMS's signals?

Regards,

Marek

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