Hi,
Yesterday and today, I experience several "Low voltage alarms" reported on the CerboGX web page (Multiplus II 48/5000/70-50, Pylontech batteries 4.8 kWh, connected to grid and SMA solar inverter). The latest alarm occurred at 23:14, which corresponds to the last hole in the voltage and current curves.
The same holes can be found on the SOC curve:
Any idea of what is going on?
Thanks in advance.
Can the Pylontech's BMS disconnect the battery? If it can, then that would also lead to Cerbo shutting down (so gaps in monitoring) even during the day since there is no MPPT to power the DC side. Just a guess. I might be completely off-track on this.
Some (or nearly all) of the gaps that can be seen during the past days are disappearing when zooming in. This is probably a minor bug in VRM display. Today, I had another alarm a 2.32 pm and by chance I was in front of my Victron at that time. That's the first time I notice it, the red led (low battery) was on, Cerbo was off (all leds switched off), last battery SOH a few minutes before at 100%, no particular load active, battery was still on (according to the battery leds). Afterwards, I regret to not have measured manually the voltage at battery output (to check your guess). The system restarted itself without any manipulation. This time the gap is much larger (30 minutes before the alarm) and it does not disappear when zooming in. Does the BMS reports a wrong value to VE.bus? Or is it a voltage measurements on DC input within the Multiplus?
Low battery LED on Multiplus and Cerbo turning off do point towards a disconnected battery.
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When the system is working normally, measure the battery voltage with a multimeter and compare it to the reported value.
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Do you have DVCC on in Cerbo? It should be on.
You might need to reduce the Absorption voltage (at least for testing).
From the graph it seems that you now have it set at 52.4V. That's not particularly high for LiFePO4, as long as the cells are well matched and well equalized (same charge level). You can reduce it to 52V and see if it helps.
Alarms occur even if the solar power is around its maximum. It never occurs when the battery is under charge, always when it is discharging or idle. Usually Cerbo GX reboots (why? Internal firmware error or short battery disconnection?), it is not available for a few minutes and upon start-up an alarm is thrown. When the Cerbo GX is not available (I've no idea of its state because it does not respond on its web page), the measured DC voltage is fine (manually measured).
DVCC is Forced on, the Absorption voltage is configured at 52V. In the graphs, it oscillate around 52 V. I don't know if it is normal, but I guess so.
The first alarm in this sequence started from August 13th at 6.49 pm. On August 13th in the morning, I modified DVCC settings to limit charging power to 0 W until noon (I needed power to charge the car and I did not want to spend power charging the home battery) and then to 500 W (10A, instead of 1700 W in configuration, there is so much sun power available during Summer that battery gets to 100% in all cases). This limit of 500 W remains until now. There is a so high correlation between these alarms and the modification of DVCC settings that I will revert to the configured limit, at least for testing. I'll see if alarms continue to occur.
