Anyone else had grief with their Victron MultiPlus tripping on high loads — 12v 3000VA model?

Been scratching my head with this one for a few days now. Running a Victron MultiPlus 12/3000/120 in my off-grid cabin setup, fed by a 400Ah LiFePO4 bank (4x 100Ah 12v cells in parallel). Everything's been rock solid for months, but lately it's tripping on overload whenever I try to run the kettle and the microwave at the same time — roughly 2800W combined. The inverter should handle that fine in theory, shouldn't it?

The weird thing is it doesn't trip immediately — it runs for maybe 20–30 seconds then shuts down with the overload LED flashing. Battery voltage looks healthy at around 12.8–13v under load according to the BMV-712, so I don't think it's a low-voltage cutoff situation. Cables are 70mm² from battery to inverter, maybe 80cm run, so I'd hope that's not the bottleneck.

I've had a poke around in VictronConnect and nothing obvious is jumping out at me. Wondering if the inverter temperature has anything to do with it — the unit is mounted in a fairly enclosed wooden cabinet. Has anyone else seen this kind of behaviour, or managed to narrow down whether it's a thermal issue, a cell balance problem, or something in the settings I've missed?

DodgySpanner | Posts: 847

@Chunk66 Classic symptom with that unit on 12v — you're asking a lot of current from the battery side. At 3000VA output you're potentially pulling 300A+ from a 12v bank, and that's before inverter inefficiency. Your BMS is almost certainly the culprit; most LiFePO4 batteries have overcurrent protection set conservatively from the factory, sometimes as low as 100A per cell.

Check what your individual battery BMS units are rated for and whether they're daisy-chained in any way that could cause one to trip and cascade. Also worth checking your busbar connections and cable gauge — voltage sag on undersized cabling can look identical to an overload trip.

What's the actual load you're running when it drops out? Kettle? Shower pump? Knowing the spike vs steady draw would help narrow it down considerably.

MarkGibson | Posts: 312

Had almost identical grief last winter with my garden office setup — same unit, similar battery config. The penny dropped when I checked my cable run: I'd used 70mm² cable but the connections at the battery terminals were the weak point. Volt drop under surge was enough to trigger the low-voltage cutoff before the battery actually needed it.

Worth logging the DC voltage right at the MultiPlus terminals during the trip using a Victron BMV-712 or similar. If you're seeing it dip below 10.5v momentarily, your cabling or terminal resistance is the culprit rather than the inverter itself.

Also check your BMS discharge rate limit — some cheaper LiFePO4 cells will throttle hard under surge even when showing 90% SOC. Fogstar Drift cells are decent for handling that kind of instantaneous demand, for what it's worth.

HarbourKev | Posts: 1,204

@Chunk66 worth checking your battery interconnects before anything else. I had the same drama on my narrowboat — turned out the parallel busbars were undersized and the voltage was sagging just enough under surge load to trigger the low-voltage cutoff on the MultiPlus. Looked fine on a multimeter until I actually loaded it up and watched the BMS panic.

Grabbed a proper clamp meter and measured each cell's contribution under load — one connection was doing almost nothing. Single dodgy crimped lug, that was it.

Also worth logging via VictronConnect during the trip — the history screen will tell you whether it's overcurrent, low voltage, or overtemp shutting it down. Saves a lot of guesswork. Those 12v units are hungry beasts; at 3000VA you're pulling 300+ amps from the bank and every milliohm matters.