Multiplus Inverter will not invert from 12v to 240v when off grid

Had similar issues with mine in the static caravan last winter. Turned out it was a combination of things worth checking:

First, the obvious bits:

• Is the Multiplus actually set to inverter mode? Check the settings via VE.Configure — mine was stuck in charger-only by default
• Check your DC switch is actually on and feeding power to the unit
• Battery voltage needs to be above the low voltage cutoff threshold (usually around 10.5v on a 12v system)

What actually fixed mine:
The shore power detection was the culprit. Even though we'd disconnected from mains, the unit thought it was still there. Had to manually toggle the "Use AC input" setting or do a full power cycle on the DC side.

Also worth verifying your battery bank voltage is stable — if you're dropping below about 11.5v under load, the inverter won't wake up properly.

Worth asking:
What's your battery setup like? If you're running a smaller bank, you might be hitting voltage sag when the inverter tries to fire up. I learned that the hard way.

Has anyone else run into the Multiplus being stubborn about inverting? Curious if there's a firmware version thing or if it's just temperamental on smaller systems. Might be worth checking if yours needs an update too.

@Midge52 good shout on the mode setting. I'd add that if it's definitely in inverter mode, worth checking whether the remote control (if you're using one) is actually communicating properly. Had that exact issue myself last year — inverter looked fine but the remote wasn't paired correctly.

Also, what's your battery voltage actually reading when you're trying to invert? Mine kept dropping below the threshold during high loads and the Multiplus would just cut out. Sorted it once I realised my battery cables were undersized for the current draw.

One more thing — if you've got a grid connection coming in, make sure the AC input breaker isn't tripped. Sounds daft but the Multiplus gets confused if it detects any grid voltage, even a dodgy one.

What error codes are you seeing on the display, if any?

Yep, mode setting catches everyone out. But if that's sorted, worth checking your DC supply voltage — Multiplus won't invert below about 10.5V, and if your battery's drooping under load, it just won't fire up. Pop a multimeter across the battery terminals while you're trying to invert something.

Also check the remote on/off switch if you've got one fitted — easy to overlook. And if you're running it off leisure batteries in a van setup like mine, make sure they're actually charged. Sounds daft but I've done it.

What's your DC voltage reading showing when you try to invert? That'll narrow it down quick.

Worth checking your DC breaker hasn't tripped — mine went into thermal cutoff in the caravan when I tried running the kettle and charger simultaneously, absolutely silent about it too. Also verify your battery voltage under load; if it's sagging below 10.5V on 12V systems, the Multiplus will just sit there like a sulk and refuse to play. Had to upgrade my battery bank and add a second Victron BMV to actually see what was happening. If the voltage holds steady and mode's confirmed, check whether grid code is enabled — sometimes gets ticked by default and locks you out when mains isn't present.

Worth adding to @Spud's point — check the actual voltage at the Multiplus terminals, not just at the battery. Cable resistance can be deceptive. I had this exact issue in my caravan; thought the battery was fine at 12.8v, but only 11.2v was reaching the inverter due to dodgy crimps on the main run.

Also worth verifying the Multiplus firmware is current. There were some quirky edge cases with older versions where it wouldn't reliably switch to invert mode, especially if the AC input had been recently disconnected.

If you've ruled out mode, voltage, and breakers, check whether the remote on/off is engaged. Sounds daft but worth mentioning — mine came with the remote control and the unit wouldn't invert until I realised the remote had it disabled.

What's your battery voltage reading at the Multiplus itself?

@BayJason's absolutely spot on about that voltage drop — I've seen folks bewildered by a perfectly happy battery showing 13.2V whilst the Multiplus terminals are gasping at 11.8V. Cable resistance is a sneaky bugger.

Since you've got the mode and DC supply sorted, worth inspecting the actual cables too. Dodgy

Good points all round — one thing nobody's mentioned yet: have you checked the low voltage cutoff setting in VEConfigure? Out of the box the Multiplus can be quite conservative, and if your battery is even slightly discharged it'll refuse to invert before you'd expect it to.

Also worth asking — what battery chemistry are you running? If it's LiFePO4 with a BMS, the BMS itself might be cutting the load rather than anything Multiplus-related. Fogstar Drift cells in particular can drop out silently if the BMS trips.

Can you post a screenshot of your VictronConnect status screen when it's refusing to invert? That'll show exactly what state it's reading and whether it's a protection trigger or a config issue.