Victron Multiplus tripping on startup with my workshop lathe - any ideas?

Had the exact same issue when I first tried running a compressor off my Multiplus-II 3000. Induction motors are brutal on startup — the inrush can be 6-8x the running current, which catches the inverter completely off guard even if the running load looks fine on paper.

Few things worth trying:

• Check your assistant settings in VictronConnect — specifically the overload trip delay. You can sometimes tweak this to give it a bit more headroom before it throws in the towel
• PowerAssist — if you've got any grid or shore power available as backup, enabling this can help bridge that startup spike
• Soft starter — genuinely the easiest fix. Picked up a cheap one for around £40 and it transformed things. Fitted it inline with the motor and the startup draw dropped massively

Also worth knowing what your battery setup is. If you're on lithium (I run Fogstar cells) the BMS can sometimes be the culprit rather than the Multiplus itself — a sharp inrush triggers overcurrent protection on the battery end and the whole thing collapses before the inverter even reacts properly.

What size Multiplus have you got and what's the lathe motor rated at? A 5.5kW motor on a 3kVA inverter is just never going to work without a soft starter regardless of settings.

Others on here have had good results with the Victron ESS assistant tweaks too — worth a search through the old threads.

What's your current battery bank and cable setup like? Undersized cables can make this significantly worse.

@BatteryMark is right about the inrush, but worth also checking whether your Multiplus is set to the correct UPS mode vs standalone — I had mine misconfigured and it was far more sensitive to transients than it should've been.

Also, PowerAssist settings in VEConfigure are worth a look. If your AC input limit is set too conservatively it can cause odd behaviour under heavy motor loads.

What battery chemistry are you running? My LiFePO4 bank handles the surge better than my old AGM setup ever did — the BMS response time matters too, some cheaper units will disconnect under the spike before the inverter even has a chance to ride it out.

A soft starter on the lathe motor would probably sort this permanently though. Relatively cheap fix compared to the headache.

Soft-starter module — sorted mine when the Multiplus was having a meltdown every time my static van's aircon kicked in. Markon do a decent one, or if you're feeling fancy, the Victron ESS assistant has a "motor start" threshold you can tweak in VE.Configure. Also check your battery cables aren't undersized — a voltage sag on startup looks identical to an overload trip and half the threads on here turn out to be 16mm² cable trying to do a 50mm² job. What's your battery bank? If it's a single 100Ah Fogstar you're flogging a dead horse regardless of settings.

@Rob1963 beat me to the soft-starter mention, but worth adding — on a lathe specifically, check whether it's a single-phase or three-phase motor first, because the solution differs significantly.

If it's single-phase, a capacitor-start motor will have an even nastier inrush spike than a standard induction motor. I run a metal lathe on my Multiplus-II 5000 and had to do two things:

1. Raise the AC input current limit in VictronConnect temporarily
2. Enable PowerAssist so the battery backs the grid/generator during startup transients

Also check your PowerControl settings — sometimes the Multiplus is simply trying to protect a smaller generator input and throttling too aggressively.

What's your battery bank capacity and C-rate capability? If you're on lithium with a BMS that's voltage-sensitive, the BMS itself can disconnect under load spike before the Multiplus even reacts, which looks identical to an inverter trip but isn't.

@24V_Queen makes a good point about single-phase vs three-phase — worth finishing that thought because it matters a lot here.

On my narrowboat I ran a small metal lathe for years off a Multiplus 24/3000. The thing that nobody mentions is PowerAssist — if you've got shore power or a genny feeding in alongside the inverter, make sure PowerAssist is actually enabled and tuned properly in VictronConnect. Mine was set too conservatively and the Multiplus was essentially fighting itself on motor startup.

Also check your DC cable sizing to the batteries. A marginal connection that's fine under normal load will cause a voltage sag exactly when inrush hits, which the Multiplus reads as a fault condition and shuts down. Traced that one on my setup to a slightly loose busbar connection — embarrassingly simple fix after two days of head-scratching.

Right so picking up where @24V_Queen left off — single-phase lathes are generally fine with a soft-starter sorted, but if yours is three-phase you're looking at a whole different headache because the Multiplus is single-phase output only. You'd need a VFD (variable frequency drive) between the inverter and the motor, which also handles the soft-start issue in one go — two birds, one stone situation.

I had something similar when I was trying to figure out my EV charging setup and kept chasing the wrong problem entirely before someone pointed me toward the actual root cause.

What's the nameplate on your lathe saying? Single or three-phase, and what's the rated running wattage? That'll tell us whether a simple soft-starter sorts it or whether you're down the VFD rabbit hole.