Inverter only / charger only while feeding to the grid + genset

Been thinking about this a lot lately after a chat with a fellow motorhome owner who runs a proper home backup setup too.

So the scenario I keep coming back to — has anyone here run a Victron Quattro (or similar) in a configuration where it's acting purely as an inverter from batteries/solar when the grid quality is rubbish, whilst simultaneously keeping a genset in the loop for charging only?

My situation isn't quite at the "two 10kVA Quattros" level 😄 but I do run a modest backup setup at home alongside my motorhome rig, and I've noticed the grid here can be absolutely filthy — voltage spikes, weird harmonics, the lot. Some of my more sensitive electronics have clearly taken a battering over the years.

What I'm wondering is:

• Can you configure a Quattro to ignore the grid for output (so your sensitive loads only ever see clean inverted power) whilst still letting it feed back excess solar, and use a genset purely in charger mode?
• Has anyone actually done this in a UK residential setup? I imagine the G98/G99 export rules throw a spanner in the works

I've had a poke around in VictronConnect and the ESS settings but it's doing my head in a bit. Would love to hear from anyone who's cracked this — installers or DIYers both welcome. Fogstar cells, Victron kit, UK grid connection... surely someone here has wrestled with exactly this?

@ExTrucker73 yes, running a Quattro in inverter-only while simultaneously charging from a genset is literally what the Quattro is designed for — it's not a hack, it's a core feature. The transfer switch handles the genset input on AC-in-1, your grid export goes out AC-out-2 (if your DNO allows it and you've got the right G98/G99 cert sorted).

Worth noting though — grid feedback via AC-out-2 needs ESS configured properly in VE.Configure, and your installer needs to set the grid code correctly for UK regs. Got this running on my shepherd's hut setup with a Fogstar Drift LiFePO4 bank behind it.

The bit most people trip over is the anti-islanding requirement — Victron's ESS handles it but your DNO will want paperwork. What's your battery chemistry?

Great thread this. @ExTrucker73 to add to what @BatteryWez is getting at — the Quattro's real party trick is that Input Current Limit feature, so you can throttle back what it draws from your genny while still letting the inverter side top up any deficit from the batteries. Dead useful when you're running a smaller genny that can't cope with full charging current plus your loads simultaneously. Worth having a proper poke around in VEConfigure if you haven't already, specifically the "PowerAssist" settings. Makes the whole thing feel quite seamless in practice. One thing I would flag — if you're also thinking about grid feedback, double-check your DNO situation first. Some are still a bit sticky about it depending on your connection agreement.

Good points from @BatteryWez and @DontPanic44 already. Worth adding: if you're running a Quattro in a grid-tied scenario with a genset on AC input 2, pay close attention to the PowerAssist limits on each input independently. I had mine configured wrong initially on my narrowboat setup — the transfer switch logic was pulling from the wrong input under load, which confused the BMS no end.

Also worth noting: VE.Configure lets you set different current limits per input, so your genset (say, a 3kVA unit) won't get overloaded when the Quattro decides to top up the batteries mid-cycle. The Quattro won't export to the grid from AC input 2 by default either, which is the behaviour most people actually want. Check your ESS assistant configuration carefully — that's where most of the gotchas live.

Great thread. To build on what @FenlandSolar mentioned about grid-tied scenarios — the bit people often miss is PowerControl and PowerAssist working together here. When grid is present but weak (think shaky rural hookup or a wobbly genset), the Quattro won't just passively charge; it'll dynamically limit its AC input draw so you never pop the supply breaker. Crucial if you're EV charging simultaneously — my setup pulls hard from the inverter side while the Quattro politely throttles back its grid appetite.

Also worth flagging: ESS Assistant configuration in VE.Configure is what unlocks proper grid-feedback behaviour. Without it correctly set, you'll get unexpected relay behaviour. Victron's ESS documentation is dense but genuinely worth an afternoon with a brew. The Victron Community forum has some cracking worked examples for exactly this topology.

Really useful thread this. Quick question building on what @DailySolar mentioned about PowerControl — does that behaviour change at all when you've got a genset on Input 1 and grid on Input 2 simultaneously?

Asking because on my boat I've occasionally had both connected (harbour shore power plus a small Honda), and I was never quite sure whether the Quattro was genuinely prioritising intelligently or just defaulting to whichever input it detected first.

Also — for a tiny house emergency backup scenario, is there a practical limit to how frequently you can switch between inverter-only and charger-only modes without stressing the unit? Wondering if frequent switching is something to avoid or whether the Quattro handles it without complaint.