Quattro: Second input is not supported correctly

Been running a similar-ish setup on my narrowboat for a while now, and this particular quirk of the Quattro has had me scratching my head more than once.

My situation: shore power on AC-in-2, a small Honda generator on AC-in-1, and a Fronius Symo feeding into the AC side. What I've noticed is that when the Quattro switches between inputs — particularly when the generator kicks in — the system doesn't always cleanly prioritise things the way you'd expect from reading the manual. The Fronius occasionally throws a fault and drops off entirely, which rather defeats the point.

My suspicion is that the ESS assistant isn't fully accounting for AC-in-2 as a "valid" input in certain edge cases, especially when there's AC generation already present on that bus. Has anyone else seen this?

A few things worth checking if you're troubleshooting:

• ESS assistant version — older versions had known quirks around dual-input handling
• AC input current limits set correctly for both inputs in VEConfig
• Grid code settings — UK G98/G99 compliance can interact oddly with the Fronius depending on firmware

I've been digging through the Victron community forums and there are threads going back years on this, but nothing that feels like a definitive fix for UK installations specifically.

Would be really interested to hear if anyone here has cracked it — particularly those running a Quattro in a mobile or off-grid context where generator + shore power switching is a daily reality rather than an occasional thing.

@WattAMess25 — you've hit on something that caught me out badly during my first winter on the cut.

The Quattro's AC-in-2 is fundamentally a "generator input" in Victron's logic, even if you're feeding it shore power. It doesn't support PowerAssist on that input — only AC-in-1 does.

What sorted it for me was reassigning AC-in-1 as my marina shore connection and treating the small genny as secondary. Sounds backwards, but the input priority and assistant behaviour follows the physical input designation, not whatever label you give it in VictronConnect.

Worth checking your ESS or generator assistant settings in VEConfigure too — there are specific tick-boxes that gate which input gets "intelligent" treatment. Took me an embarrassing amount of forum-reading and one very flat LiFePO4 bank before I pieced that together.

@WattAMess25 worth checking your AC input current limiter settings for AC-in-2 specifically — the Quattro treats the two inputs quite differently in terms of priority and PowerAssist behaviour.

On my shepherd's hut setup I found that AC-in-2 doesn't support PowerAssist at all, which catches people out when they're expecting the inverter to top up a weak shore supply. If your generator or shore connection is marginal, the Quattro may simply reject it rather than assist.

Also worth verifying in VEConfigure whether Overruled by remote is ticked for the input current limit — without that, some external controls (Cerbo GX etc.) can't actually adjust AC-in-2 limits dynamically.

What's your AC input current limit set to on that second input?

@WattAMess25 the Quattro's AC-in-2 is deliberately hobbled — it's passthrough only, no inverter support, so if your generator drops out you won't get that seamless UPS-style switchover you'd get on AC-in-1. Caught me out in the motorhome when I had shore power wired to the wrong input and wondered why the batteries weren't charging properly from the genny. Swap your shore power to AC-in-1 and generator to AC-in-2 if seamless backup matters less, or flip them entirely depending on your priority. Also worth checking in VEConfigure that AC-in-2 is actually enabled — it defaults to disabled on some firmware versions, which makes the whole thing look broken when it's just asleep on the job.

@MarineGeoff has nailed the core issue — passthrough only is the key thing people miss. Worth adding though: if your shore power on AC-in-2 drops out even briefly, the Quattro won't seamlessly bridge the gap from inverter the way it would on AC-in-1. Found this out the hard way when my marina supply got flaky one winter.

If you can rewire to put shore power on AC-in-1, do it. Yes it means juggling your generator priority settings, but at least you get proper UPS-mode behaviour.

If rewiring isn't practical on the boat, make sure your transfer switch delay is set as low as possible in VEConfigure — won't fix the fundamental limitation but reduces the glitch window somewhat.