ESS Minimum SOC jumps to 98% under high load – bug ? unexpected behavior?

[TheRealStefan]

Hi everyone,

I’m running a Victron ESS setup with the following configuration:

• CerboGX at v3.70~25 (upgraded from 3.64 final) both versions are showing the behaviour

• 3x Multiplus-II 5000 in 3-phase setup

• 4x 16kWh batteries

• ESS mode enabled

• Minimum SOC set to 20%

Under normal conditions (e.g. ~1kW load), everything works as expected: the system maintains the minimum SOC at 20%, and the batteries discharge accordingly.

However, when I switch on my EV wallbox and the load increases to ~12kW, the system suddenly stops discharging the batteries. I noticed that the ESS minimum SOC jumps to 98% without any manual change. As a result, the batteries stop discharging because the new minimum SOC is reached.

Once I turn off the wallbox, the minimum SOC drops back to 20% and the system resumes normal behavior.

Interestingly, if I manually reset the minimum SOC back to 20% while the wallbox is active, the batteries discharge as expected again.

Has anyone experienced this behavior? Is there a setting or logic in ESS that dynamically adjusts the minimum SOC based on load? Or could this be a bug or misconfiguration?

BTW, I never set the minimum SOC to 20%. It came during my tests when it dropped back from 98% to 20%.
I had set it to 8% initially.
Also the min SOC under load seems to match the actual battery SOC. (I just tried again with a SOC of 95%).

Thanks in advance for any insights!

As this sound very crazy I tried to create a video.

~10 sec load turned on
~30 sec minimum SOC Change to 98$
~38 sec load turned of
~40 sec minumum soc returned to 20%

[Janvi]

What kind of batteries and wallbox do you have and how they are coupled with the ESS?

[TheRealStefan]

Not sure how relevant it is…

It is a Sungrow Wallbox only logically connected to the ESS System (on the AC-In path).
I have an EM24 LAN Powermeter to measure the load. This meter is configured with the EV-Charger Role.
The Wallbox itself sits on the AC-in path.

Main ESS Meter is a Victron VM-3P75CT directly after the “official” grid meter.

Batteries are DIY presented via Battery Safety Controller (via CAN).
Batteries can deliver far more power than the 3x5Ks can pull as an inverter.

There are no loads on AC-Out other than a few small PSUs.
However a couple of micro inverters sit on AC-Out.

No DC Solar. Main Solar is on the AC-In Path.

The question is what changes the ESS Minimum SoC from the value I set it to the actual battery SoC when there is a certain load and why is it then set back to 20% (instead of my value) when I turn of the load.

When I “overdrive” the min-Soc to lets say 10% when this bad-magic happens ESS#1 turns off and the inverter delivers 250+A from the batteries.

[TheRealStefan]

I just figured out that it was my fault.

It is related to the EVCC settings (should have mentioned that I use EVCC to controll my wallbox).
There is a small switch to dissallow discharge of the battery under certain conditions.

This seems to be done via manipulating min ess soc.

Stupid me