question

This is most likely caused by a cell imbalance in the Pylontech battery,

The procedure for how to manage this is described here (it says high voltage, but it is very similar)

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#high_voltage_warning_or_alarm_shown_on_battery_status

If you’re unable to resolve it with those directions, come back and we can investigate further.

@Guy Stewart (Victron Community Manager) thanks for the fast reply. I've just checked VRM and at the precise time this happened both the min and max cell voltages were identical:

Do you still think I should follow the Victron guide to balance the cells or is this issue likely to be something else?

Is there a way to make the multiplus pass power through from the grid when these alarms happen rather than take the house out?

Cheers!

Hi @pauldunn,

I had a closer look at the alarm and it appears to co-incide with the EV charging station starting.

A 7000 W load starts, and then whatever the underlying problem is revealed.

It doesn't appear to happen every time, so requires some combination of factors, most likley co-inciding with a low battery state of charge, and no voltage support from PV.

There is another element, there appears to be up to a 0.3V difference in the battery voltage between the two parallel MultiPlus-IIs. It really important for equal power distribution of large loads through these two units that they are very well balanced, otherwise one will be working harder than the other. And then again combined with the lower voltage situation, and large load spike, we see the alarm.

As there are several factors, there are several possible solutions.

1. Only run the EV charger when the batteries are quite full (say above 80% SOC), or the sun in shining on the solar panels
2. Check the battery conditions to make sure they appear ok visually, although I would say this is less likely the main cause now, it should still be inspected.
3. Reduce the charging power of the EV charger until it stops being such a large load, I would expect if it was under the capacity of a single unit (5000W) then there would be no alarm as well
4. Check all cable connections to the Multis, specifically the DC. If the cables are equally sized, and equally distant from the DC bus, then check to make sure connections are tight and fuses are intact, because there is a variation somewhere there.

Hi @Guy Stewart (Victron Community Manager)

The EV charger is upstream of the inverters and I don't use a CT clamp, the only loads the inverter knows about is out of AC OUT 1, so I assume we can rule that out of being part of the cause?

All cable lengths are equal both to the inverter and to the consumer unit on AC OUT 1 but I will double check the connections. Is there anything else that could cause the imbalance? The inverters were bought at different times not sure that could be an issue?

Four of the batteries are 1.5 years old and the other two are 1 years old and I cannot see anything visually wrong with them though it is hard to see without complete disconnecting and moving them. Is it worth doing that?

Cheers