Generator keeps cutting out mid-cycle - is it the AVR or something else?

Had this exact drama with my old Kipor last winter — turned out to be the AVR slowly dying, but only under load, which made it an absolute nightmare to diagnose.

Classic signs it's the AVR rather than something else:

• Voltage creeps up or down just before it cuts
• Happens more when you're running something with a big inductive load (fridges, pumps, motors)
• Cuts out but restarts fine with no fault codes

That said, before you chuck money at a new AVR, worth ruling out the boring stuff first — blocked air filter, fuel starvation (gummed-up carb jet if it's been sitting), or a low oil pressure cutoff triggering falsely. My cabin genny once had me convinced it was electrical when it was just a partially blocked fuel line causing it to starve under load.

A cheap multimeter on the output while it's running will tell you a lot — if you're seeing voltage swing wildly before the cut, AVR's almost certainly your culprit. Genuine replacements are pennies on eBay for most Chinese units, though quality is a lottery.

Also — what brand/model is yours? Some of the older Hyundai and Champion units have a known weak AVR design that cooks itself if you run near rated load for extended periods. Victron users here often just parallel a proper inverter setup and use the genny purely for charging, which sidesteps a lot of this grief.

What's the load profile when it's cutting — is it predictable or random?

@BatteryGill the load-dependent failure is such a cruel one to chase down.

What caught me out on my narrowboat was similar — the generator looked fine at idle, voltage steady as anything, but the moment the inverter-charger pulled hard, it would collapse. Turned out the AVR was thermally failing; fine cold, falling over once it warmed up under demand.

Worth grabbing a cheap clamp meter and watching the AC voltage while applying load progressively. If you see it sag then recover, sag then cut entirely — that thermal/load combination points squarely at AVR rather than, say, a fuel delivery issue or a failing capacitor on a brushless unit.

Replacement AVRs are surprisingly affordable. Dropped about £18 on a generic unit for my old Hyundai before eventually upgrading properly. Bought the generator another two winters of honest service.

@BatteryGill AVR failure under load is textbook, but worth ruling out a few other culprits first before condemning the AVR unit itself.

On my static caravan setup I had identical symptoms — dropout only at 60-70% load — which I initially blamed on the AVR. Actually turned out to be a failing capacitor on the exciter winding. Much cheaper fix.

Quick diagnostic checklist before replacing the AVR:

• Check output voltage with a decent multimeter under progressive load — AVR failure typically shows voltage collapsing rather than cutting out cleanly
• Inspect the brush gear if accessible — worn brushes cause remarkably similar symptoms
• Check your fuel delivery under sustained load (partially blocked carburettor jet is a classic Kipor gotcha)

If voltage is oscillating wildly before dropout, that's your AVR. If it drops steadily, look upstream at the mechanical/fuel side first.

@FormerTeacher61 makes a fair point about ruling things out systematically. On my boat setup I've seen identical symptoms caused by a failing capacitor on a brushless exciter — visually fine, but capacitance had dropped well below spec. A cheap capacitor tester (sub-£15) will confirm or eliminate that quickly before you start pricing AVR replacements.

Also worth checking: fuel delivery under sustained load. A partially blocked carburettor jet will often hold RPM at no-load but starve the engine once you pull real current, which then collapses the field voltage and looks identical to AVR dropout on the output waveform.

If you have a multimeter, log your AC output voltage at no-load versus, say, 50% and 80% load. A healthy AVR should hold within ±2–3V across that range. If it's sagging 10V+ under load, that narrows things considerably.

@FormerTeacher61 and @RiverRunner both raise good points about systematic diagnosis. One thing that tripped me up during my van conversion build — fuel starvation can mimic AVR symptoms almost perfectly under load. Cheap generators especially will sag at the carb when you throw a proper load at them, voltage drops, inverter trips, and you're left chasing electrical ghosts.

Before swapping the AVR, I'd check:

• Fuel flow under sustained load
• Capacitor on single-phase units (often the actual culprit)
• Brush condition if it's a brushed alternator type

The capacitor is stupidly cheap to replace and kills the AVR diagnosis theory stone dead if swapping it fixes things. Mine was a £4 part from eBay that saved me buying a whole AVR module. Worth 20 minutes of your time first.

Something nobody's mentioned yet — have you checked your fuel cap vent? Sounds daft, but a blocked vent creates a vacuum in the tank and the engine starves under load, cutting out in a way that looks electrical rather than mechanical. Took me embarrassingly long to figure that one out on my Honda.

Also worth checking the hour meter if you have one — if it's anywhere near service intervals, a partially blocked fuel filter will cause exactly this under sustained load. Easy and cheap to rule out before you start pulling the AVR.

@RussGreen curious what eventually gave your situation away in the end? Sometimes the final clue is obvious in hindsight but invisible when you're stressed and cold in January trying to keep the batteries topped up! 😄