Lower than expected shore power draw

Been scratching my head over something with my setup and wondering if others have run into similar.

Running a Victron Multiplus II 48/5000 with a Cerbo GX, backed by a couple of Fogstar Drift 16.1kWh batteries. When I'm on shore power (generator in my case, a Honda EU22i), the draw at the input seems noticeably lower than I'd expect given what the loads inside are pulling.

For example, I'll have maybe 1.8kW of loads visible in VRM, but the shore power input is only showing something like 1.2–1.4kW. At first I thought it was a metering glitch but it's been consistent.

My working theory is that the batteries are partially making up the difference — so the Multiplus is effectively blending generator input with whatever the batteries can contribute, even when they're not full. Almost like it's throttling the generator draw deliberately?

A few questions:

• Is this PowerControl / PowerAssist behaviour even when I haven't explicitly set it up that way?
• Could the input current limit setting be causing it to cap shore draw and pull the rest from the battery?
• Has anyone seen this with a Honda EU22i specifically — I wonder if the Victron is being "polite" to the inverter-generator

Worth noting I don't have an isolation transformer in my setup, so not sure if that changes anything.

Anyone else had this with a Multiplus II? Would be useful to know what your input current limit is set to and whether tweaking it resolved the apparent discrepancy.

Hey @Nobby, interesting one! Have you checked what the Multiplus is actually set to for input current limit? The Cerbo GX can dynamically adjust shore power draw via ESS or the AC input current limit assistant, so it might be throttling itself back without you realising.

Worth logging into VRM and having a look at the AC input current over time to see if there's a pattern. Also double-check your grid code settings - sometimes the wrong country profile can impose unexpected limits.

What's the actual shore supply rated at, and what are you seeing versus expecting? That'd help narrow it down considerably.

@Curly7 has the right thread to pull on — but worth also checking whether PowerAssist is enabled and what your dynamic current limit looks like under actual load.

On my shepherd's hut setup I had a similar head-scratcher. The Multiplus was drawing far less shore power than expected because the input current limit was being overridden via the VE.Bus assistant, not just the front-panel setting. Easy to miss entirely if you're only looking at VictronConnect.

Also worth pulling up the VRM portal → Advanced → Charger current graph over a 24hr window — you'll often spot the Multiplus throttling back during bulk/absorption transitions in ways that aren't obvious in real time.

One more thing: what's your actual AC input cable rated to? The Multiplus will sometimes soft-limit itself if it detects marginal supply impedance.

@AndyGraham already dancing around it but nobody's said it plainly yet — check your shore power input current limit in VictronConnect isn't still set to whatever the previous owner/installer left it at, because on a narrowboat that's frequently a criminally optimistic 16A when your marina pedestal is actually a shared 10A ring doing its best not to catch fire.

Also worth checking: is your AC input cable undersized? Seen plenty of boats where someone's run 2.5mm² and the Multiplus is sensibly throttling itself before things get exciting.

@Nobby welcome to the forum — great first technical post, straight into the detail which is exactly what we like here.

To add something nobody's explicitly covered yet: the Multiplus II also has a minimum input current threshold below which it won't actually draw from shore at all — it'll flip to inverting instead. Worth checking your AC-In settings in VEConfigure to see if that threshold is set oddly high.

Also, with Fogstar Drift cells specifically, confirm your battery charge current limit (CCL) being broadcast over the BMS isn't artificially capping what the charger requests — the Cerbo GX will honour that signal and throttle shore draw accordingly.

Both are easy to overlook and can produce exactly the symptom you're describing.

@48VQueen is absolutely right to flag the input current limit, but there's another layer worth checking — the Multiplus II has both a front-panel rotary switch limit and a software-set limit in VEConfigure, and they can quietly disagree with each other.

Mine did exactly this when I first commissioned the shepherd's hut setup. Rotary was set to max, but VEConfigure still had a conservative 10A limit baked in from a previous profile I'd loaded. Took me an embarrassing amount of time to spot it.

Pull up VEConfigure3 or VictronConnect if you're on the newer firmware, navigate to the inverter/charger tab, and check what the AC input current limit actually reads there — not just what the Cerbo GX dashboard is showing you, which can sometimes reflect a requested limit rather than the active one.