Victron Multiplus tripping out when microwave kicks in — is it the surge?

Had this exact issue last year with my Multiplus 2 (3kVA). Microwave was constantly tripping it out — turned out to be a combination of the surge and the PowerAssist settings not being configured properly.

Few things worth checking:

• What's your AcInputCurrentLimit set to? If it's too low, the Multiplus can't blend grid/shore power fast enough when the surge hits
• Dynamic current limiter — worth enabling in VEConfig if you haven't already. It gives the inverter a bit more headroom to ramp up without tripping
• Battery state — if your bank is low or your BMS is throttling output, the inverter won't have the grunt to absorb that initial spike

Microwaves are notoriously spiky — the magnetron startup can pull 2–3x the running wattage for a fraction of a second. My old 800W microwave was pulling nearly 2.2kW on startup according to the Cerbo logs.

Also worth checking which transfer switch speed you're on. Fogstar Drift cells can handle high discharge bursts fine, but if your system is grid-tied and the transfer isn't fast enough, you get a brief undervoltage that causes the trip rather than the surge itself.

What inverter firmware are you on? There were some known issues in older versions with overload sensitivity being a bit hair-trigger.

Anyone else had this on a purely off-grid setup (no grid input at all)? Curious whether it behaves differently without the PowerAssist logic in the mix.

@Tel1968 interesting that PowerAssist configuration played into it — that's not something I'd have immediately considered.

Quick question before I dig into my own settings: what transfer switch speed did you end up landing on, and did you adjust the AC input current limit at all as part of the fix?

I've got a Multiplus 2 (2kVA) in my garden office and a fairly modest 200Ah Fogstar Drift LiFePO4 bank behind it. Microwave is only 800W rated but I've been measuring the inrush with a clamp meter and it's spiking noticeably higher. Wondering whether my battery's BMS cutting in momentarily is compounding the issue rather than it being purely an inverter configuration problem.

Has anyone verified whether the Multiplus is actually logging these trip events anywhere in VictronConnect, or would I need VRM portal access to see that data?

@Tel1968 worth checking your AC Input Current Limit in VE.Config as well — if that's set too conservatively it'll clip before PowerAssist even gets a chance to compensate properly.

Also, what's the microwave rated at? Cheap inverter microwaves (the ones with the small transformers) tend to have nastier inrush than you'd expect from the nameplate wattage. I had a similar faff with my shepherd's hut setup — swapped to an inverter-type microwave and the surge profile was dramatically cleaner.

One other thing: check your Dynamic Current Limiter setting. On older firmware it defaulted off, which means the Multiplus isn't adapting to the actual inrush curve at all.

@Tel1968 had the same faff with my static — microwave would nuke the Multiplus every single time, turned out my Transfer Switch was set to hair-trigger sensitivity and the inverter was trying to handshake with the grid feed whilst the magnetron was already demanding its pound of flesh.

Worth checking your UPS Function setting too — disabling it slightly loosens the transfer timing and stopped mine throwing a wobble mid-baked-bean situation.

Also if you're on a smallish battery bank (mine's Fogstar Drift 200Ah), the low voltage cutoff can trip before the overload protection even gets a look-in — so what looks like a surge issue is actually just your cells crying.

VictronConnect live graphs will show you exactly which threshold is crying uncle first.

@Tel1968 mine sorted itself once I bumped the Dynamic Current Limiter on — apparently it gives the Multiplus a bit of a heads-up before the surge hits rather than just getting blindsided like a goalkeeper facing a penalty in the dark 🔦