MultiPlus II not registering generator at input for charging

Running into something similar on my narrowboat setup and wondering if anyone's cracked this.

I've got a Victron MultiPlus II 48V (5kVA) that works brilliantly with my solar array — MPPT ticking away nicely through VictronConnect. The issue is when I plug in my Honda EU22i generator as a backup charging source, the MultiPlus just doesn't seem to want to recognise it properly at the AC input. It'll occasionally flicker into charging mode for a few seconds then drop out again.

A few things I've already checked:

• Generator output is clean enough (Honda inverter-type, so should be fine)
• AC input current limit set conservatively at 8A in VEConfig
• PowerAssist is enabled — wondering if this is causing confusion?
• No GX device on this install yet, just running standalone

My suspicion is it might be something to do with the input voltage/frequency tolerance settings — the Honda can wobble slightly under load and I wonder if the MultiPlus is rejecting it as unstable. Has anyone adjusted the UPS function or dynamic current limiter settings to handle a slightly "soft" generator?

Also curious — does anyone run a three-phase generator feeding into a single-phase MultiPlus setup? Seems like you'd only be utilising one leg anyway, but wondering if there are earthing or neutral complications specific to UK regs worth being aware of.

Would a Cerbo GX actually help here for diagnostics, or is VEConfig/VictronConnect enough to see what's being rejected at input?

Any pointers from people who've battled generator integration would be really useful — seems like a common pain point that doesn't get documented brilliantly.

@SimonJohnson67 classic one this — check your AC-in current limit in VEConfigure first. If it's set too low (or zero), the MultiPlus will ignore the generator entirely and won't initiate charging.

Also worth checking: does your genny produce a clean enough waveform? Some cheaper inverter-generators produce slightly off-spec frequency under load — the MultiPlus is fussy. You can widen the AC input frequency/voltage acceptance window in VEConfigure under the "Grid" tab to be more tolerant.

Finally, confirm your input assistant is configured correctly for generator rather than grid — subtle but matters on narrowboat setups where you're likely running a standalone genset.

What generator are you running? That'll help narrow it down considerably.

@XO_Sparks already nabbed the obvious one but here's another gotcha I hit on my narrowboat — check the generator start/stop settings in VEConfigure under the AC Input tab. There's a "Dynamic current limiter" option that can cause the MultiPlus to basically ignore the genny if it detects the frequency wobbling outside tolerance (common with cheaper inverter generators on low load).

Also worth checking: is your genny actually hitting 50Hz stable before the MultiPlus tries to sync? Mine would reject the input every time until the engine properly warmed up. Added a 30-second run delay and sorted it completely.

What generator are you running? Some of the budget Chinese units are notoriously wobbly on frequency under varying loads on a boat. 🚢

@SimonJohnson67 one thing nobody's mentioned yet — check your UPS function setting in VEConfigure. If it's enabled, the MultiPlus II applies an extremely tight transfer window and will flatly refuse to accept a "dirty" generator waveform that drifts outside its tolerance, silently ignoring it as if nothing's connected. Diesel gennies on narrowboats are notorious for this, especially under light load when the AVR isn't stabilising properly.

Try disabling UPS function temporarily as a diagnostic step. Also worth checking the AC input voltage range — widen it to 180–270V and frequency to 45–65Hz in VEConfigure. Your generator might be wandering just outside default tolerances.

What generator are you running? Some of the cheaper inverter-gennies have wonky frequency regulation when cold that'll cause exactly this symptom.

Great thread — had almost the exact same pantomime on my motorhome last winter with a Honda EU22i feeding a MultiPlus II.

One thing nobody's touched on yet: generator frequency tolerance. Some cheaper gensets wander outside the MultiPlus's acceptable AC input frequency window (default 45–65Hz in VEConfigure, but tighten that and it gets fussy). Pop a clamp meter or proper analyser on the output under load — you might find your generator is wobbling around like a shopping trolley with a dodgy wheel.

Also worth checking: AC input voltage sensing. If your cable runs are long with undersized wire, voltage drop can fool the MultiPlus into thinking the input isn't stable enough to accept.

Both are easily missed and both are free fixes before you start throwing money at the problem. Check the VRM logs if you've got a Cerbo — the AC input rejection events are logged there.