Can i set the Cerbo GX to turn on the inverter when the batteries are fully charged

This is something I've been tinkering with on the boat actually, so it's close to my heart.

The Cerbo GX absolutely can do this via the Generator Start/Stop logic, but what you're really after is using it to trigger the inverter rather than a genny. The relay outputs on the Cerbo can be configured with custom conditions — battery State of Charge thresholds being one of the most useful.

What I ended up doing was using a VE.Bus Smart Dongle setup with a scheduled assistant on the Multiplus, combined with SOC-based conditions. Essentially:

• Inverter enables when SOC hits 95%+
• Cuts off again when SOC drops below 80%

This stops the fridge from draining the bank overnight when the solar's doing nothing. The hysteresis is the critical bit — without it you'll get the inverter chattering on and off as it teeters around the threshold.

The Victron ESS Assistant is worth looking at too if you haven't gone down that route. It handles this kind of logic quite elegantly, though it's a bit overkill if all you want is to power one appliance opportunistically.

One thing to watch: some compressor fridges — even dual-fuel ones — don't love being switched mid-cycle. Worth checking whether yours handles the handover gracefully or throws a wobbly.

Has anyone here done this with a non-Victron inverter talking to a Cerbo via the relay outputs? Curious whether the same logic holds or whether you end up having to bodge it with something like a Shelly relay in the middle.

@BoatIan interesting one — does the Generator Start/Stop logic introduce any noticeable delay between the batteries hitting 100% and the inverter actually kicking on? I'm thinking about this for EV charging at my place, where I want to dump excess solar into the car once the bank is full rather than let it sit idle.

Also, is there a minimum SOC threshold you can set so it cuts the inverter back off if clouds roll in and the batteries start draining back down? That would be the critical part for my use case — don't want to be pulling from the bank mid-charge without realising it.

Running a Victron Multiplus II here if that's relevant to how the logic behaves differently vs a boat setup.

Jumping in here — @OakSoul raises a fair point about delay, but in my experience with the Node-RED flow editor on the Cerbo it's worth considering as an alternative to the Generator Start/Stop logic. You get much finer control over the triggering conditions and can add hysteresis properly so the inverter isn't constantly chattering on and off around the threshold.

The Generator Start/Stop route works but it was really designed with, well, generators in mind, so some of the labelling and logic can feel a bit clunky when you're repurposing it for inverter control.

@BoatIan — are you triggering purely on SOC percentage or are you using voltage as the condition? On a boat with potential voltage sag I'd lean toward SOC if your battery monitoring is solid.

@BoatIan on my narrowboat the Cerbo's Modbus TCP route is what actually saved me from all that Generator Start/Stop faff — you can just write directly to the inverter's switch register and trigger it on any condition you like, including 100% SOC. Dead reliable, no weird relay logic involved. @Squib19's Node-RED approach works too but fair warning: every VRM firmware update has at least a 40% chance of quietly breaking your flows at the worst possible moment.

Good thread. I've been down this rabbit hole on my narrowboat.

One thing nobody's mentioned yet — if you're using Victron's VE.Bus system, you can set the MultiPlus switch state directly via the Cerbo using VE.Bus System Configurator. Combined with a simple SOC condition in the GX settings, this gives you clean inverter on/off control without needing Node-RED or Modbus TCP at all.

The key question I'd ask @BoatIan — what's actually driving the need for this?

• If it's load management, there's arguably a simpler path via scheduled charging and AC output assistant rules
• If it's genuinely SOC-triggered, the above approach works reliably in my experience

What MultiPlus version are you running? The older 24/3000 behaves slightly differently to the newer units with the firmware that supports remote switching properly.

@ExFirefighter genuinely curious what Vic-word you're about to drop on us — feels like being cut off mid-prophecy.

That said, from my cabin setup: Assistants in VEConfigure is the unsung hero here — specifically the Programmable Relay assistant lets you trigger outputs based on SOC thresholds without needing Node-RED or Modbus faff. Pair it with a Cerbo relay and you're basically done before your tea goes cold.

@SophieHill @ExFirefighter knowing this forum it's either VictronConnect, VEBUS, or "Vic from the pub who wired his narrowboat with Christmas lights and a prayer" — all equally valid solutions in my shepherd's hut experience.