Multiplus 2 AC Out 2 Relay with assistants cycling on/off

Been having a frustrating one with my static van setup and wondered if anyone else has run into this.

I've got a Multiplus II 2x120V (yes I know, long story) paired with a Cerbo GX, and I've been trying to use AC Out 2 as a managed load — basically to shed the immersion heater when battery SOC drops below a threshold. Set it all up using Assistants in VE.Configure and it seemed fine initially.

The problem is the relay appears to be cycling on and off repeatedly rather than holding its state cleanly. It's not a gradual switch — more like it's flickering every few minutes. Immersion heater is clicking in and out constantly which can't be doing the element any good.

A few things I'm wondering:

• Is there a hysteresis issue with how the Assistant thresholds are configured? I've got SOC set to drop AC Out 2 at 50% but wondering if it's hunting around that value
• Could this be a firmware interaction — I'm on fairly recent versions but not the absolute latest
• Has anyone successfully used the Generator Start/Stop or ESS Assistant logic instead of the dedicated relay assistant to control AC Out 2 more stably?

My Fogstar 48V battery has its own BMS talking to the Cerbo via CANbus, so SOC readings should be reasonably solid — it's not like the figure itself is bouncing around wildly.

Would really appreciate hearing from anyone who's got AC Out 2 relay control working reliably. What's your Assistant setup actually look like?

Hey @YorkshireCamper, the 2x120V unit does throw a few curveballs when it comes to assistants - worth mentioning which firmware you're running on the Multiplus II as there were some known relay cycling bugs in older versions that Victron quietly fixed.

One thing I'd check first is whether your AC Out 2 load is causing a voltage dip that's triggering a low battery condition, which then drops Out 2, load disappears, voltage recovers, Out 2 re-enables... and round it goes. Classic feedback loop.

What's your battery voltage doing during the cycling? If you've got the Cerbo logging it should be easy to spot the pattern. Also, have you got any conflicting assistants loaded? Sometimes the ESS assistant and a custom relay assistant will fight each other something rotten.

What assistants are you actually running?

Seen this exact thing on a standard 230V MultiPlus II setup actually. AC Out 2 relay cycling is almost always the assistant logic fighting itself — usually when you've got the Generator or Grid setpoints clashing with a keep-batteries-charged assistant running simultaneously.

What firmware are you on? Pre-500 had some nasty bugs with relay oscillation. Worth checking in VE.Config whether your AC Out 2 is being controlled by more than one assistant at once — that'll cause exactly this behaviour.

Also @YorkshireCamper — the 2x120V variant has different default relay behaviour anyway, so whatever fix you find online for the EU units might not translate directly. Victron's own assistant documentation is vague at the best of times.

Cerbo logs will show the relay state changes — pull those first before guessing.

Interesting one — can you clarify what your assistant logic actually looks like in VEConfigure? Specifically:

• What's the trigger condition for the AC Out 2 relay?
• Is it using SOC, voltage, or a DVCC signal as the threshold?
• What's your hysteresis set to?

Asking because on my garden office setup I had a similar cycling issue and it turned out my hysteresis window was too narrow — the relay was toggling at almost exactly the battery voltage measurement interval. Widening the hysteresis by about 0.5V stopped it completely.

Also worth checking whether your Cerbo GX firmware matches your Multiplus II firmware expectations — mismatched versions can cause assistant states to behave oddly. What versions are you running on both?

Not directly related to the assistant logic, but worth ruling out — what's your battery voltage doing during the cycling? I had something similar on my shepherd's hut build where the relay was chattering because the SOC was hovering right on the threshold I'd set, causing the assistant to flip back and forth repeatedly.

Ended up adding a hysteresis gap in VEConfigure — so it wouldn't re-enable until SOC was a few percent above the cutoff point, not just at it. Completely sorted it.

Also, are you monitoring this on the Cerbo's VRM data? The logging granularity should show you whether it's voltage sag or a genuine assistant logic issue triggering the relay. Might help narrow it down before digging deeper into the 2x120V specifics @SmartSolarMaster raised.