Anyone else had grief with a Victron MultiPlus 12/3000 tripping on overload when running a microwave?

Right, so I've been pulling my hair out with this for the past week or so. I've got a MultiPlus 12/3000/120 running off a 200Ah lithium (LiFePO4) bank, and every time my other half bungs a jacket potato in the microwave — a bog-standard 800W Tesco own-brand job — it trips the overload alarm within about 30 seconds. The MultiPlus is set to shore power assist mode and we're connected to a 16A hookup at the mo, so it shouldn't even be leaning on the inverter that hard.

I've had a poke around in VictronConnect and the dynamic current limiter is switched on. From what I can tell the microwave is actually pulling closer to 1,100–1,200W at the wall (measured with a cheap plug-in energy monitor), which I know microwaves tend to do, but that's still well within the 3,000W continuous rating. The DC voltage looks stable — sitting around 13.1V under load — so I don't think it's the battery sagging and triggering a low-voltage cutoff.

Has anyone seen this with the 12V version specifically? I wonder if it's a surge/inrush thing that's catching it out rather than sustained draw. I've seen some chat about tweaking the PowerControl settings in VEConfigure but I'm wary of poking around in there without knowing what I'm doing. Any pointers gratefully received.

@Spud17 classic issue this. Microwaves are notorious for pulling 2-3x their rated wattage on startup — a "700W" microwave can spike to 1,800W+ for the first few cycles of the magnetron.

Few things worth checking:

• VE.Configure — what's your overload trip delay set to? Default is quite aggressive. Bumping it slightly gives those inrush spikes room to breathe
• Shore power input current limit — irrelevant here but confirms your config isn't corrupted
• Battery cable gauge and connections — a 12V/3000W system pulls 250A+ at peak. Undersized cables cause voltage sag which the MultiPlus interprets as overload

My shepherd's hut setup had identical grief until I ran proper 70mm² cable all the way to the battery with Anderson connectors. Instantly resolved.

Also worth checking the PowerControl and PowerAssist settings in VE.Configure — PowerAssist can supplement from battery during spikes even when grid-tied.

Hey @Spud17, worth checking your MultiPlus transfer switch settings too — specifically the "PowerControl" and overload trip threshold in VEConfigure. By default the overload response can be quite aggressive. You can sometimes soften this by adjusting the UPS function setting, which affects how the unit responds to sudden load spikes.

Also, what's your battery cable setup like? Even decent lithium cells can't compensate for undersized or lengthy cabling — voltage sag under that initial surge can cause the inverter to panic and trip before the battery's actually hit its limit. I'd want to see 70mm² cable minimum on a 3000W unit, ideally kept as short as physically possible.

What firmware version are you running? There were some known quirks in older builds around overload detection sensitivity.

Hey @Spud17, one thing worth checking that nobody's mentioned yet — have a look at your DC side. A 200Ah lithium bank is fine on paper, but if your battery cables are undersized or have a dodgy connection, voltage will sag under that microwave surge and the MultiPlus can interpret that as an overload condition rather than a battery issue. Also worth checking what BMS you're running; some LiFePO4 units have a fairly aggressive overcurrent threshold that'll disconnect momentarily, which the inverter then sees as a fault. What gauge are your battery cables and how long's the run? I've seen people cured of exactly this problem just by going up a cable size or properly torquing their terminals. Sounds daft but it's surprising how often it's the basics! 🔧

My van's MultiPlus threw a tantrum over a 900W microwave until I bumped the overload trip delay up a notch in VictronConnect — buys it just enough time to survive the startup surge without nuking the session mid-jacket-potato.

Slightly different angle here — has anyone looked at the battery cable gauge and length running to the MultiPlus? I went through something similar with my setup and it turned out my 25mm² cables were just a touch too long, causing enough voltage drop under surge that the inverter was seeing a false low-voltage condition and tripping out rather than a true overload.

Worth checking your Victron CCGX or GX Touch logs if you have one — it'll tell you exactly why it tripped (overload vs low DC voltage) rather than guessing. The fault codes are genuinely useful here.

@FEE_Solar makes a good point about the bank size too — what BMS are you running? Some cheaper units will throttle current hard on any spike.

Hey @Spud17, good shout from @RogerJackson on the cabling — worth eliminating that first. One thing nobody's touched on yet though: have you checked the PowerAssist settings in VE.Configure? If your shore/generator input is connected at all, PowerAssist can sometimes interfere oddly with peak demand handling. Also, microwaves are notorious for having a magnetron startup spike that's considerably higher than the rated wattage — your 800W model might be pulling 1400-1600W for that first second or two. Worth checking the actual wattage printed inside the door rather than going by what's on the box. Some cheaper microwaves are genuinely horrible for this. What brand/model is it? That might help narrow things down. 🙂

Been through exactly this on my narrowboat with a 750W sharp microwave — drove me absolutely spare.

What nobody's mentioned yet: check your battery BMS discharge current limit. My Fogstar cells were perfectly healthy but the BMS was set conservatively from factory at around 80A continuous. A microwave's startup surge can briefly demand 250A+ from a 12V bank — BMS sees that, panics, disconnects, and the MultiPlus reads it as an overload.

Log your battery voltage during the fault with a Victron MPPT or BMV if you've got one. If it's collapsing below 11V for even a fraction of a second before tripping, your BMS is the culprit, not the inverter.

Ran into this exact nonsense on my static caravan last summer. The bit nobody's mentioned yet — check your PowerAssist settings in VEConfigure. If it's misconfigured, the MultiPlus won't pull from the battery fast enough when the microwave's magnetron kicks in and demands surge current. That split-second gap is enough to trip the overload protection before PowerAssist even wakes up.

Also worth knowing: microwaves lie about their wattage. A "700W" machine can pull 1,100W+ at the wall. Measure it with a clamp meter before you go chasing ghosts elsewhere.

@RustyCaptain replied:

@Spud17 worth checking your PowerAssist settings in VictronConnect if you haven't already. The MultiPlus can pull from the shore/generator input to supplement the inverter during heavy loads — if that's misconfigured or disabled entirely, it's all falling on the inverter alone. Also, what's your low voltage cutoff set to on the LiFePO4? If the BMS is momentarily sagging under that microwave surge and triggering a protective disconnect, the MultiPlus will see that as an overload event. Stick a battery monitor on it and watch the voltage during the fault — that'll tell you a lot straight away.