Low Battery voltage without reason

DIY
, , , , ,
1

Hello community!

I am getting frustrated with Cerbo GX, which now is beeping “Low Battery Voltage” at 48% SOC, seemingly without any reason.

I’ve even reset again the Multi RS to it’s factory settings and again set:

  • 280 Ah battery
  • 80 A charging current (conservative value, battery capable of 200 A)
  • Absorption Voltage: 56.8V (conservative, could go to 58.4 V)
  • Float Voltage: 54.4 V (conservative, could go to 55.2 V)
  • Low Voltage Alarm and Restart: 44.8 V
  • ESS: Optimized without Battery life
  • AC input to connect only at state of charge at 20%
  • Victron connect also shows it’s controlled by BMS
  • DVCC is enabled with only “Shared Current” option enabled, I think it was default.

The JK-BMS is giving me firm data about the battery, voltage holds perfectly at 52.53V which corresponds to 48% SOC, Charge is ON, Discharge is ON, cells are perfectly balanced. No warnings shown.

obrazek
obrazek329×581 73.6 KB

Two days ago the messages started to appear at 48% SOC and since then, basically the battery is in that state and it is neither charged or discharged. I even disconnected AC input yesterday and let it on solar only Today, but the battery is shown as “Idle” in the VRM and meaningles back-and-forth charging and discharging by like 25 W is shown in Victron Connect, only adding to my confusion.

Some insight for what could be a reason for that could be a custom widget I created in VRM, that shows this:

obrazek
obrazek306×378 39.3 KB

It doesn’t make any sense and doesn’t correspond with the reality, it seems to me. But if this is what the Multi RS is seeing, then it explains the warnings. This beeping came back even now, when the loads (and grid) are disconnected, only solar and battery is connected. So with no loads whatsoever.

The battery producer doesn’t know how to help me, they don’t yet understand the new Multi RS ecosystem and their instructions related to ESS aren’t helping much.

Looks like the problem is not with Multi RS and battery, but Cerbo GX. I wonder, if the DVCC settings is incorrectly set or what.

Any ideas appreciated :slight_smile:

2

This voltage is the voltage reported by the Multi RS to Cerbo and Cerbo is only collecting it and sending it to VRM.
Also based on this voltage, the Cerbo gives you the alarms.

Please check the battery to Multi RS connections. Also any power switches or fuses if you have ones.
If you have a bad connection (high resistance) this is how it looks.

Also can you plot the battery voltage reported to Cerbo and then to VRM by the battery BMS and compare it with the Multi RS voltage?
This if you connected the battery BMS to Cerbo on BMS CAN…

3

Tank you very much @alexpescaru,

It all makes sense, what you’ve explained.

Guided by your advice, I was able to plot BMS-reported voltage (bellow the Multi RS voltage):

Screenshot_20241023_094242_Opera
Screenshot_20241023_094242_Opera1398×2437 169 KB

I will inspect the connections to the battery, if I’ll be able to access the terminals at MultiRS, I will measure it at the battery, at the invertor and combinations (+ battery, -invertor and vice versa).

I suspect the 100A circuit breaker/fuse can be the problem; it was replaced once and looks “cheap”. I tried to buy better one back then, but they mostly look same “quality” and even appearance, but will try to buy from some good brand this time.

I need to replace it with higher rating anyway, since battery is capable of 200A, Multi RS theoretical maximum is ~125A, so I think I can buy 150A DC circuit breaker, set charge/discharge maximum to 120A and reality will be max 100A.

I will report how it went, for others future reference.