Generator surging with MultiPlus-II 3000VA and other questions

Been wrestling with a similar setup in my tiny house build and wanted to get some collective wisdom going here.

Running a Victron MultiPlus-II 3000VA (24V) paired with Fogstar Drift 24V 200Ah LiFePO4 batteries, and I've been pulling my hair out with generator surging issues. My genny is a Honda EU22i (the UK equivalent of the 2200), and when the MultiPlus is in charge-only mode and the batteries are significantly depleted, the generator hunts noticeably — that classic rhythmic surging that sounds like it's about to give up.

From what I've diagnosed so far, the issue is the MultiPlus demanding charge current faster than the EU22i's inverter-generator can ramp up to meet it. The fix most people land on is ramping down the charge current in VE.Configure — I've dropped mine to 18A and it's settled considerably, though not entirely.

A few things I'm still investigating:

• PowerAssist calibration — whether tweaking the AC input current limit affects surge behaviour under combined load + charge scenarios
• UPS mode vs. charger-only mode — does it make a difference for generator stability?
• Whether the Dynamic Current Limiter setting in VE.Configure actually helps with inverter-generators specifically

This is primarily an emergency backup system for me, so the generator doesn't run often — but when grid goes down mid-winter I need it to work.

Anyone else running a Honda inverter-gen with a MultiPlus on a 24V system? Particularly interested in whether Cerbo GX + generator autostart changes the equation at all, since that's my next planned addition.

@CrispyRoamer what generator are you running with it? That's usually the first question because the MultiPlus-II is notoriously fussy about generator quality — it needs a clean sine wave and stable frequency.

The PowerControl and PowerAssist settings in VictronConnect can make a big difference. I had surging issues with mine until I dropped the AC input current limit right down and let PowerAssist do the heavy lifting from the batteries. Counterintuitive but it smoothed everything out.

Also worth checking your UPS function setting and whether weak AC is enabled in the advanced settings — that's specifically designed for generator input.

What does VRM or the GX device show for AC input frequency during the surging? That'll tell you pretty quickly whether it's a generator regulation problem or a MultiPlus configuration issue.

@Thommo is right about the generator being key, but also worth checking your transfer switch settings in VEConfigure.

Had exactly this surging issue on my narrowboat — turned out the AC input current limit was set too aggressively. The MultiPlus was essentially fighting the genny trying to pull more than it could cleanly deliver.

Few things to try:

• Lower the AC input current limit (I dropped mine to 8A initially then crept up)
• Enable UPS function if you haven't already
• Check the weak AC setting under grid tab — genuine game changer with smaller inverter-generators

Also worth noting the 3000VA 24V has a relatively high idle current draw, so if your generator is undersized it'll hunt continuously trying to keep up.

What's the rated output on your generator? Makes a big difference whether it's a proper inverter-type or a conventional AVR unit.

@CrispyRoamer I had nearly identical grief when I first ran my MultiPlus-II 3000 off a generator on the narrowboat. The surging was maddening — turned out the UPS function was the culprit. Go into VEConfigure and look at the AC input current limit. Mine was set aggressively low, so the MultiPlus kept wrestling with the genny for control.

Also worth checking: dynamic current limiter — tick that box if you haven't. It lets the MultiPlus smooth out those generator load spikes rather than fighting them.

The Fogstar Drift pairing should be solid, but make sure your battery absorption/float voltages are configured correctly for those cells. Fogstar publish recommended Victron settings on their site — saved me a phone call.

What's your generator's rated wattage versus actual output? A cheap 3500W unit often delivers closer to 2800W continuous, which causes exactly the symptoms you're describing.

Good timing on this thread — I've been through exactly this headache getting my garden office setup dialled in.

One thing nobody's mentioned yet: check your UPS function setting in VEConfigure. When I had surging issues, disabling the UPS function (or adjusting the input current limit down gradually) made a huge difference. The MultiPlus-II was essentially fighting itself trying to compensate.

Also worth looking at the AC input voltage range — mine was set too tight by default, so the unit kept dropping in and out when the generator wobbled slightly under load.

What's your input current limit set to? I run mine conservatively at around 10A even though my generator is rated higher. Lets the Fogstar pack do the heavy lifting during peaks rather than hammering the genny.