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

Had this exact drama on my boat last summer — turned out to be the AVR slowly dying but pretending to be fine until it absolutely wasn't, classic.

Few things worth checking before you splash out on a new AVR though:

• Fuel flow — dirty carb or partially blocked filter can cause it to load-hunt and cut under demand
• Capacitor on the exciter winding — these fail silently and mimic AVR death convincingly
• Brushes — if you've got a brushed alternator head, worn brushes cause dropout under load exactly like you're describing

The "mid-cycle" detail is interesting — is it cutting at a consistent load point, like when something big kicks in (fridge compressor, inverter charger pulling hard)? On my setup I've got a Victron Multiplus and the inrush when it goes into bulk charge has killed lesser gennies.

What make/model is the generator? Some of the cheaper Kipor-style units have notoriously flakey AVRs that are actually a fiver on eBay — genuinely, the replacement is sometimes better than the OEM part because the OEM was rubbish to begin with.

Also worth sticking a clamp meter on it while it's running to see if voltage is collapsing before it cuts — if voltage drops first, AVR or capacitor; if it just dies with no warning, look at thermal cutouts or the engine side.

Don't bin it yet — these things are almost always fixable if you're willing to poke around a bit. What are you running off it?

@MarineKaren Know that feeling well — sneaky faults are the worst to diagnose! One thing I'd add that caught me out: check your excitation winding resistance with a multimeter when the generator is cold versus after it's been running 20-30 minutes. I had a genny that tested perfectly cold but the winding insulation was breaking down thermally, so it'd only misbehave once it warmed up. Classic intermittent fault that mimics AVR issues. Also worth checking your carbon brushes if it's a brushed alternator — worn brushes cause voltage wobble that looks identical to AVR failure on the symptoms side. Cheap fix if that's your culprit. What make/model is the generator? Some AVRs are dead easy to swap yourself, others are a right faff.

Great thread, @MarineKaren — sneaky intermittent faults are genuinely maddening.

One thing nobody's mentioned yet: check your generator's brush gear if it has any. Worn or sticking brushes can cause exactly this kind of mid-cycle dropout that looks for all the world like an AVR issue. I wasted nearly two weeks suspecting my AVR before noticing one brush was hanging up in its housing rather than tracking the slip ring properly.

Also worth logging the coolant temp when it cuts out — I've seen what presents as an electrical fault actually be a thermal cutout doing its job because the cooling fins were blocked with debris. Quick clean and the "electrical fault" vanished entirely.

Borrow a multimeter with a logging function if you can, so you're capturing what's actually happening at the moment of failure rather than guessing after the fact.

Bit of a tangent but worth raising — if it's cutting out mid-cycle specifically (rather than randomly), look hard at your load profile. I had a similar saga with my static caravan setup; turns out the compressor on the fridge was creating a spike on startup that pushed the generator briefly into overload. AVR took the blame for months.

Quick sanity check before replacing anything:

• Log your load with a clamp meter during the fault
• Check whether the cutout coincides with any appliance cycling on
• Inspect the brushes if it's a brushed alternator — worn brushes mimic AVR failure convincingly

Victron's Cerbo GX is brilliant for capturing these transient events if you've got one in the system already. Replacing an AVR blind when the root cause is elsewhere gets expensive fast.

Really resonates with my shepherd's hut setup — I ran a petrol genny through two winters before the solar took over properly, and intermittent cuts drove me absolutely mad.

One angle nobody seems to have covered yet: fuel starvation mimicking electrical faults. My old Hyundai would cut mid-cycle under load because the carburettor needle valve was partially gummed up. Voltage looked fine on the Victron, engine sounded healthy right up until it didn't. Classic red herring.

Worth ruling out before you pull the AVR apart:

• Fuel filter condition (surprising how quickly they clog)
• Carb bowl — any varnish deposits?
• Does it cut sooner when the tank's lower (suggesting float issues)?

@BayJason's point about mid-cycle specifically is interesting — if yours is load-triggered rather than time-triggered, that narrows things considerably.