Anyone else had grief with low voltage cutoff on a Victron MultiPlus when running heavy loads?

Been scratching my head with this for a couple of weeks now. I've got a MultiPlus 12/3000/120 paired with a 200Ah lithium (a Fogstar Drift if it matters) and a 40A Victron SmartSolar MPPT. When I kick on my kettle or the induction hob — anything pulling over about 1500W — the inverter trips out on low voltage even though the battery is sat at a healthy state of charge. Talking 80-90% SOC, so it shouldn't be anywhere near the cutoff floor.

From what I can tell, it's the voltage sag under load that's triggering the protection rather than the actual capacity being low. The MultiPlus is set to cut at 11.0V and I suspect the internal resistance of the battery plus the cable run (about 1.5 metres of 70mm² from battery to inverter) is dragging the voltage down just long enough to trip it. I've bumped the cutoff down to 10.5V as a test and it does seem to help, but I'm a bit wary of going much lower and stressing the cells.

Has anyone dialled in a sensible low voltage cutoff setting for a similar 12V lithium setup, or is there a way to add a short time delay before the cutoff triggers? I know VEConfigure lets you tweak some of this but I haven't had a proper dig into it yet. Wondering if I'm missing something obvious.

@BatteryDoug — classic MultiPlus gotcha, this one. Had almost identical grief with my motorhome setup last summer.

The thing people miss is that under a heavy load, the voltage at the battery terminals can sag significantly even with a healthy lithium. The MultiPlus is seeing that sag on its sense wires and cutting out thinking the battery is flat — when it's nowhere near it.

Two things worth checking:

• DC cable sizing — undersized cables cause serious voltage drop under load. The 12/3000 can pull ~300A peaks.
• Low voltage cutoff settings in VEConfigure — the default values aren't always ideal for lithium. Your Fogstar Drift's BMS cutoff and the MultiPlus cutoff need to play nicely together, with the MultiPlus cutting first.

Remote voltage sensing cables direct to the battery terminals made a noticeable difference on mine.

Great thread, @BatteryDoug. Worth checking your DC cable sizing between the battery and the MultiPlus — even a short run of undersized cable can cause enough voltage drop under that 3000W load to trip the low voltage cutoff, even when your battery still has plenty left in it. The MultiPlus sees the terminal voltage, not the actual battery state.

I'd suggest logging with VictronConnect or VRM if you've got that set up, so you can see exactly what voltage it's reading at the moment it shuts down. My bet is you'll find it's a voltage sag issue rather than the battery genuinely hitting its limit.

Also worth double-checking your DC fuse and busbar connections are properly torqued — loose connections make this significantly worse under heavy load.

Seen this exact thing with my setup. The MultiPlus has dynamic cutoff enabled by default — it raises the low voltage threshold under heavy load to protect against voltage sag tripping the BMS.

Worth jumping into VE.Configure and checking your dynamic cutoff curve. If your Fogstar's BMS is also set conservatively, you're effectively getting a double-whammy — the inverter backs off before the BMS even has chance to react.

I knocked my dynamic cutoff values down slightly after logging with VE.Bus Smart Dongle and saw the actual battery voltage was nowhere near as low as the inverter was assuming. Made a noticeable difference on kettle/microwave spikes.

Also worth confirming @BarryCrane's point about cable sizing — even 10cm of undersized cable adds enough resistance to cause grief at 3kW draw.

@BatteryDoug — @PennineSolar is spot on about dynamic cutoff, and @BarryCrane's point on cable sizing is worth taking seriously too.

One thing nobody's mentioned yet: check your DC ripple voltage under load. With a 3000W inverter pulling serious current from a 12V system, you're talking 250A+ peaks. Even a well-specced cable run can show significant voltage sag at the battery terminals versus what VictronConnect is actually reading at the MultiPlus sense points.

Worth grabbing a decent DC clamp meter and measuring directly at the battery terminals while under load. If you're seeing more than 0.5V difference between there and your MultiPlus connections, that's your culprit rather than any settings issue.

Also double-check your battery's BMS discharge rating — some Fogstar Drift configs have conservative continuous discharge limits that interact badly with brief heavy loads.

Good shout from @PennineSolar and @BarryCrane — both valid points. One thing I'd add that caught me out on my own 12V MultiPlus setup: check your battery's internal BMS communication. If you're not using a VE.Bus BMS or at least a proper DVCC setup via Cerbo/Venus, the MultiPlus is essentially guessing at battery state. The Fogstar Drift has a decent BMS but without closed-loop communication, the inverter's acting blind under surge loads. Also worth looking at your DC fuse rating — I had a slow-blow fuse that was subtly current-limiting under heavy draw before it ever blew properly. Threw me off for ages. What loads are you actually running when it trips? Knowing whether it's a sustained draw or a startup surge would help narrow it down considerably.

What @Keith1981 and the others haven't mentioned — check your DC system voltage is actually reading correctly in VictronConnect. Had a nightmare on my shepherd's hut setup where the voltage sense was reading at the MultiPlus terminals rather than the battery terminals. Voltage drop under load meant it was seeing maybe 11.8V when the Fogstar itself was sat at 12.4V.

Easy fix — enable the remote battery sense if your Fogstar supports it (Drift should via the BMS), or run a separate sense wire directly to the battery terminals. Made a massive difference for me. Worth ruling out before you start fiddling with dynamic cutoff curves.