Problem with low voltage at the generator

Had a similar headache last year with my Victron Multiplus-II and a cheap diesel genny — worth sharing in case others are going through the same.

The generator I was using (a Hyundai 6.5kW, no AVR) was throwing out voltage that wandered all over the place under load — sometimes dipping to 205V, occasionally spiking past 250V. The Multiplus just flatly refused to accept it as a valid AC source. Frustrating doesn't cover it.

What eventually sorted it:

• Lowering the AC input low limit in VEConfig — I dropped mine to 180V as a starting point
• Disabling UPS mode — this made a huge difference, the Multiplus became much less fussy about transfer timing
• Increasing the AC input current limit gradually to avoid overloading the genny on startup

I didn't mess with country settings personally, but I've seen posts on the Victron Community forum where people running non-AVR generators in the UK have changed the frequency acceptance range slightly. Worth reading through if you're still stuck.

One thing I'd genuinely recommend — if your generator is running without an AVR and you're regularly relying on it for backup, just get an AVR-equipped machine. The Fogo units people mention seem decent but I can't speak from direct experience. Hyundai, Stephill, and Honda EU series all behave much more predictably with inverter-chargers in my experience.

Anyone else found specific VEConfig settings that work well with AVR-less generators in a UK setup? Curious whether the country standard tweak actually helps or just masks a deeper issue.

@LizStewart this rings a bell from my narrowboat days — I ran a similar rig before switching most things over to solar.

The bit that caught me out wasn't just the AVR situation, it was the interaction between the Multiplus-II's UPS function and a wobbly frequency. Cheap gennies don't just sag on voltage — they hunt on Hz too, especially under variable load. The Multiplus sees that instability and goes into a kind of defensive crouch.

Worth checking your AC input sensitivity settings in VEConfigure. There's a "wide input frequency range" option that's off by default — enabling it bought me significantly more tolerance before the inverter started rejecting the generator's output entirely.

Didn't solve the underlying problem obviously, but it stopped the constant switching-out while I sorted a proper solution.

@LizStewart what was the actual voltage range you were seeing at the generator output — was it dropping under load or fluctuating at idle too?

I ask because on my narrowboat setup I had a similar situation where the Multiplus-II was throwing low AC input alarms, but the root cause turned out to be a combination of weak AVR and undersized cable run from the genny to the inverter. Voltage drop across cheap 2.5mm² flex made a borderline situation into an unacceptable one.

Worth checking:

• Input sensitivity settings in VEConnect — the Multiplus can be configured to accept a wider AC input range
• Cable gauge and run length to the genny
• UPS function enabled or disabled

Did you log the AC input voltage via the Cerbo or VRM portal? That data would tell you exactly what the Multiplus was seeing.

@LizStewart — the no-AVR issue is a classic trap. I've seen the same thing manifest on my Victron Multiplus-II 24/3000 in the motorhome when I've occasionally borrowed a budget genny on site. The Multiplus's input voltage window is actually fairly tight by default — worth checking your assistants settings in VictronConnect and widening the AC input low/high thresholds if you haven't already. Mine was set to disconnect at 207V which caused repeated relay chatter under load.

Also worth noting: the Hyundai HY6500LEK does have an AVR on later production runs — worth checking your serial number against their documentation, because some early units shipped without it despite the spec sheet claiming otherwise.

@ExFirefighter's question about load-dependent voltage drop is the right one to answer first — that distinguishes a weak AVR from a genuinely undersized generator struggling with reactive load from the inverter's input stage.

@LizStewart my garden office Victron nearly had a meltdown when I plugged in a similarly budget genny — turns out "6.5kW" on the sticker is doing a lot of heavy lifting as a number.