Generator keeps cutting out mid-cycle - knackered AVR or something else?

Had almost identical symptoms with my old Hyundai 3kVA last winter — intermittent cuts mid-cycle, usually after 20-30 minutes of load. Turned out to be a combination of a failing AVR and a partially blocked carburettor jet, which was causing the engine to hunt under load and ultimately trip the AVR's protection circuitry.

Before you condemn the AVR, worth ruling out the simpler stuff first:

• Check the fuel delivery — partially blocked jet causes lean running under load, RPM drops, voltage sags, AVR gives up
• Inspect the brushes if it's a brushed alternator — worn brushes cause erratic excitation
• Load test it properly — does it cut at a consistent wattage, or after a consistent time? Time-based suggests thermal; wattage-based suggests electrical

If you've got a multimeter, watch the DC excitation voltage going into the AVR while it's running. Should be stable. If it's hunting around, carb/governor issue rather than AVR.

Replacement AVRs are cheap enough (£15-40 on eBay for most Chinese-manufactured units) that it's tempting to just swap it, but I've seen people fit a new AVR only to have the same fault because the root cause was elsewhere.

What make/model is the generator, and what load are you running when it cuts? That'll help narrow it down considerably. Also — is the cut a clean shutdown or does it splutter and die? Clean cut usually points to a protection trip; splutter suggests fuel starvation or governor hunting.

Classic "two culprits, one crime scene" situation — while you're in there replacing the AVR, also check your brushes because worn brushes and a dodgy AVR often go hand-in-hand like a bad marriage. 🔧

My Victron MultiPlus throws a fit when generator output gets wobbly mid-cycle too, so I'd also stick a clamp meter on the output voltage before assuming it's purely mechanical — sometimes it's thermal runaway in the AVR capacitor rather than the AVR itself, which is a £3 fix rather than a £40 one.

@SuffolkCruiser good shout on the dual-fault scenario — that's exactly the kind of thing that sends people chasing ghosts for weeks.

One thing worth adding: thermal cutout is often overlooked entirely. If it's consistently dying at the 20-30 minute mark, that's a textbook sign the engine is hitting its temperature limit, not necessarily an AVR issue at all. Check your cooling fins are clear of debris and the oil level is correct before spending money on parts.

Also — what's the actual load you're running? A 3kVA unit being pushed to 80%+ capacity will heat up faster than people expect, especially in an enclosed space.

If you're new here and diagnosing your first generator fault, don't be put off by the complexity — this forum has brilliant collective knowledge and you'll get sorted. Stick around, plenty of good people here.

@AngliaOffGrid the ghost-chasing is real — I spent two weekends on my Kipor before realising the AVR was masking a intermittent connection on the stator winding.

Worth also checking the capacitor on single-phase AVR-regulated machines — they degrade silently and can cause exactly this symptom pattern. A multimeter won't always catch it; you really need a capacitance tester.

Also, what's the load profile when it cuts? If it's consistently after 20-30 mins under sustained load, thermal cutout on the AVR itself is another possibility. My garden office setup draws pretty steady 1.2kW and that kind of constant load exposed weaknesses my occasional-use testing never caught.

Before buying parts, photograph your existing AVR — Chinese clones vary wildly in quality even with identical part numbers.

@AlexPalmer60 the Kipor rabbit hole is a rite of passage honestly.

One thing nobody's mentioned yet — thermal cutout on the stator windings. That 20-30 minute window is a massive clue. If the AVR tests fine when cold but misbehaves under sustained load, the stator's embedded thermal protection may be tripping before the AVR even gets a chance to fail properly.

Seen this on a Chinese-badged 3.5kVA I ran off my motorhome for two seasons. Replaced the AVR twice before a sparky friend pointed at the stator temperature. Turned out the cooling fan shroud had a hairline crack — barely moving air across the windings.

Check airflow first. Dead simple, costs nothing. If the exhaust side runs noticeably hotter than usual after 15 minutes, you've got your answer before you've spent a penny on parts.