System unable to charge from generator

Had this exact nightmare on the narrowboat last winter — generator humming away like it's dead chuffed with itself, Victron MPPT sitting there doing absolutely sod all, and the battery bank slowly giving up the ghost.

Turned out the generator's voltage was just out of tolerance — reading fine on a basic meter but the Victron's input thresholds are tighter than my ex's budget. Swapped to a proper true-RMS meter and suddenly it was obvious.

A few things worth checking if you're in this situation:

• AC frequency — cheaper gennies drift, and inverter-chargers can be fussy about anything outside 49–51Hz
• Voltage under load — it might look fine at idle but sag badly once the charger tries to draw current
• Transfer switch or RCD nuisance tripping — silent killer, this one
• Charger input current limit — if it's set too low, the charger backs off and you'd never know why

This seems to be a recurring pattern — I've seen it mentioned a fair few times now, and it's almost never one obvious fault. Usually a combination of marginal generator output plus something in the settings that tips it over the edge.

Anyone else running a Victron MultiPlus or similar with a portable genny regularly? Curious whether the PowerAssist settings are causing grief for others, or if there's a generator brand that plays nicer. My ageing Honda has been solid but I know folks on here use everything from Hyundai to those suspiciously cheap units off eBay.

What's your go-to diagnostic process when the genny seems fine but the charger disagrees?

@DodgySocket classic Victron "I'm fine, everything's fine" face while the batteries quietly expire.

Nine times out of ten with this one it's the AC input voltage threshold — generators notoriously wobble outside the MultiPlus's acceptance window, especially under load. Check your Shore Input settings in VE.Configure; the default lower threshold is 180V but a wobbly genny can dip enough to confuse it.

Had this exact farce in my shepherd's hut last February. Generator was outputting 207V under load — technically within spec, but my MultiPlus had somehow got its limits configured very conservatively from a previous firmware flash.

Widened the acceptance range slightly, and suddenly: charging like a champion.

Also worth checking: is the transfer switch actually closing? You'll hear a satisfying clunk if it is. No clunk = different problem entirely.

Had this on my static caravan setup last year — turned out the generator's AC output was too "dirty" for the inverter-charger to accept. Cheap Chinese genny with horrible voltage fluctuations.

Few things worth checking:

• Is it actually an MPPT or an inverter-charger (MultiPlus etc.)? MPPT won't charge from a generator at all — it's solar only
• If it's a MultiPlus/Quattro, check the input current limit in VictronConnect — sometimes it's set absurdly low
• What generator are you running? Some need to reach proper load before the voltage stabilises enough for Victron to accept it

The Victron #10 System Time Sync or similar error codes in the logs can point you in the right direction too.

What does the CCGX/GX display actually show when the genny is running?

@JennyCole raises a good point about dirty AC — worth actually measuring it rather than guessing. Cheap multimeter won't cut it here; you need something that reads true RMS or you'll get wildly optimistic numbers while your kit quietly weeps.

On my garden office setup I had a similar saga with a cheap Chinese genny — the frequency was wandering between 48Hz and 53Hz depending on load, which made my Victron MultiPlus throw a proper wobbly. Generator's AVR was basically decorative.

Questions worth asking @DodgySocket:

• What generator model are you running?
• Have you checked the input frequency range in your Victron settings? (PowerControl tab in VEConfigure)
• Is the shore power LED on the Multi actually solid or blinking?

Sometimes bumping the input voltage tolerance wider in VEConfigure sorts it immediately. Took me an embarrassingly long time to find that setting.