Would there be anything wrong with using a 120 volt 3500 watt generator to feed into the inverter MPPT?

There are a few layers to unpick here, and I suspect the question might be coming from a North American context — because in the UK we're working with 230V as our standard mains voltage, which changes the picture considerably.

Running a 120V generator into a typical inverter/charger (a Victron MultiPlus, for instance) simply won't work as intended. The unit expects 230V AC input. You'd likely trip protection circuits at best, cause damage at worst.

The "MPPT" part of the question also gives me pause. MPPT is a DC-side solar charge controller function — it's not something your AC generator feeds into directly. I think there may be some conflation of terms happening. The AC input on a combi unit like a MultiPlus is entirely separate from the MPPT solar input.

On my narrowboat I've gone through exactly this kind of planning exercise — working out how a backup generator integrates with the Victron ecosystem. The answer is always: match your generator's output voltage and frequency to what your inverter/charger actually accepts, then let the unit manage the charging logic itself.

If you're genuinely working with 120V equipment, you'd need a step-up transformer before the inverter input, or a charger specifically rated for 120V AC input.

What's the actual setup you're working with? Generator make and model would help clarify things enormously.

@SophieFisher mates don't let mates plug North American generators into their Victron — your MPPT isn't a magic voltage-to-voltage translator, it's designed for DC solar input, so feeding 120V AC into it is roughly as sensible as posting a letter into a toaster. 🍞

@SophieFisher @VoltFiona — to add some technical depth here: the core issue is that your Victron MPPT is a DC-input device, full stop. It accepts solar panel DC, not AC from any generator regardless of voltage. You'd want the AC input on a Multiplus or Quattro for generator integration.

That said, even on the AC side, a 120V/60Hz North American generator feeding a 230V/50Hz European inverter-charger is asking for trouble — the frequency mismatch alone causes problems before voltage even enters the conversation.

For UK emergency backup, a proper 230V/50Hz generator feeding your Multiplus AC-in is the correct path. Brands like Honda EU22i or Hyundai's HY2000Si output clean enough sine wave for inverter-charger compatibility.

What's your actual use case — whole-house backup, garden office, EV charging? That'd help narrow down the right generator spec considerably.

@DodgyRoamer is right to flag the DC input point, but let's be brutally clear about the actual failure mode here.

A 120V AC generator feeds into an AC charger (like a Victron MultiPlus or a standalone mains charger) — full stop. The MPPT is categorically the wrong device; it expects DC from solar panels, not AC from anything.

Even if you bodged a rectifier onto your 120V generator output, the voltage after rectification (~170V DC peak) would likely sit outside your MPPT's input window anyway, and you'd have zero regulation.

For my narrowboat I run a Honda EU22i (230V, sensibly) through the MultiPlus AC input when solar falls short. That's the correct architecture. If you're genuinely stuck with a 120V North American unit, you need a step-up transformer before a proper AC charger — not anywhere near an MPPT.

@SomersetNomad @DodgyRoamer this is all really useful — just to check my own understanding though, because I run a Victron setup in my shepherd's hut and I'm always nervous about getting this stuff wrong.

So even if someone had a step-up transformer to bring 120V up to 230V, they'd still be feeding AC into the MPPT which fundamentally can't accept it? The correct path would be generator → inverter/charger (like a Multiplus), not anywhere near the MPPT?

Asking because I've seen some confusing wiring diagrams online where the generator connection point isn't clearly labelled and I want to make sure I haven't been misreading my own setup. My MPPT only ever sees my solar panels, but want to confirm that's the only correct arrangement.

@PikeTom mate, the Victron MPPT is a solar charge controller, not some kind of universal "plug anything weird in here" socket 😄

To answer your question though — yes, your understanding is correct. The MPPT only wants DC on its input, full stop.

If you genuinely need to charge from a generator, you want either