Multiplus II goes off during NODE-Red switching from Inverter mode to Passthrough

Q&A and troubleshooting DESS
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Hello,

I would like to ask for advice regarding the behavior of a Victron MultiPlus II inverter/charger during mode switching.

Installation is : Multiplus II 48/5000+CerboGX+SEPLOS 2.0 BMS ( 16x EVE cells = 16kWh capacity ), 3x MPPT Smart Solar

System description:

  • MultiPlus II

  • Grid Code: None

  • UPS function: enabled

  • System operated without ESS

  • AC loads supplied via AC-out

  • Mode switching is controlled via Node-RED

  • Battery SoC-based hysteresis:

    • SoC ≤ 30% → switch from Inverter to Passthrough

    • SoC ≥ 35% → switch from Passthrough to Inverter

Observed behavior:

  • The transition from Passthrough → Inverter works without any noticeable interruption. This transition appears seamless.

  • However, the opposite transition, Inverter → Passthrough, causes a short interruption:

    • The inverter output briefly switches off

    • After a short delay, the internal transfer switch closes and Passthrough mode becomes active

    • This results in a short power interruption to the house loads

Question:
Is there a recommended way (configuration or operating mode) to ensure that the transition from Inverter → Passthrough is handled purely by the internal transfer switch without any interruption of AC supply to the loads?

In other words, is it possible for the MultiPlus II (in UPS mode, Grid Code = None, no ESS) to perform a seamless transition from Inverter to Passthrough, similar to how the reverse transition already behaves in my setup?

Any insight into whether this is:

  • a configuration limitation,

  • a firmware design choice,

  • or something that can be improved with specific settings,

would be greatly appreciated.

I would more easily understand the problem occurring during the transition from Passthrough to Inverter. What is interesting is that when I look at the Advanced tab in the VRM portal, I can see that even while the MultiPlus II is in Passthrough mode, it still has real-time information about the AC In frequency (i.e., the utility grid). Because the inverter does not have to (or does it?) be running continuously even in Passthrough mode?

Thank you in advance for your time and support.

Best regards,
Marek