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roger-1 asked

Sporadic very inaccurate low battery voltage warnings from Multiplus II

Hi, I’m new to the Community and installing an ESS System with a Multiplus II 48/5000/70-50 connected to 3 x rack mounted 120Ah LiFePO4 unsupported batteries with a two wire (? Dont ask ) CAN BUS output. I have an existing grid tied 6kW SolarEdge SE6000 6kW E/W array which I have left as is.

The Cerbo GX does read the battery BMS but thinks they are LG Chem Resu so I probably will need to build a custom battery. Currently, tho, I have disconnected the BMS from the Cerbo and am using the Multiplus battery monitor. System is set to optimised without battery health. Scheduled charging at night, discharge during the day. Discharged yesterday down to circa 50V on a SOC limit of 10% before the red low voltage led came on solid accompanied by low voltage warning which kept repeating every 10 mins or so. At the scheduled charging time, 2300, no charge, red led still on. Waited 20 mins, nothing other than more low voltage warnings. Reset the Multiplus and started charging. Completed charging on reaching an indicated 95% (as set) and started discharging at 0600 as scheduled.

So the question is I don't understand what triggers the low voltage warning when the low voltage limit is not reached. Also early this morning I had another warning during the charging schedul indicating a low voltage of 42.34V which it clearly could not be as it started charging when the batteries were at 50.70?

a5c847fd-593f-42cd-b24b-26306c9e5f90.png


Will the charger not start charging if the low voltage led is on?

battery charging
a5c847fd-593f-42cd-b24b-26306c9e5f90.png (1.1 MiB)
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Alexandra avatar image Alexandra ♦ commented ·

@roger@lindleyhome.uk

You will find the battery bms is diasbling discharge or charge. Maybe at the lower level there is one or two cells lower than other due to imbalance so it is protecting itself.

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roger-1 answered ·

Hi Alexandra, thats definitely possible as all the cells are not exactly balanced. However, during the period illustrated the Can bus from the batteries was disconnected from the cerbo gx so the Multiplus could only see the combined pack voltage which was around 50V. So where Did it get the 42.34V from? That seems to me a glitch?

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Alexandra avatar image Alexandra ♦ commented ·

Do your batteries have a relay? Sometimes thise open in protection. Some bms can switch off and on again by itself in protection. It does not need comms to the system to affect the voltage to the victron. While the log shows high or acceptable voltage, the victron may have 'noticed' an interuption.

I had a supported battery do this, the bms never reported an issue. But the inverter did notice.

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