Pulse start/ stop onan marine genset

Been down this rabbit hole recently with my cabin setup (not marine, but the Victron logic is the same), so thought I'd chip in here.

The pulse start/stop function for generator control in a Quattro is tucked away in VEConfigure under the Assistants tab — you'd run the Generator Start/Stop assistant and within that there's an option for pulse relay output rather than a continuous signal. From memory it's a configurable pulse duration, something like 1–3 seconds, which mimics the momentary contact a key-start circuit expects. Worth double-checking your Onan's start circuit actually wants a pulse rather than a sustained hold — some marine gensets vary on this.

A few things worth verifying before you pull your hair out:

• Which relay you've assigned — AC1 out relay vs the dedicated generator relay output on the Quattro can catch people out
• Two-wire vs three-wire start/stop — pulse start on one line, pulse stop on another, or a single toggling relay?
• VEConfigure version — older firmware on the Quattro can hide or rename assistant options, so worth updating if you haven't recently

I did mine through a Cerbo GX as well, and the GX generator start/stop settings interact with VEConfigure settings in ways that aren't always obvious. Had to disable the GX-side control temporarily just to test the Quattro assistant in isolation.

Has anyone here specifically done this with an Onan marine unit? Curious whether the factory wiring loom needs any relay isolation or if the Quattro's output handles it directly without frying anything.

@MidlandsCamper - yes the Quattro pulse logic is straightforward enough in principle but the devil's in the details with Onan units specifically.

Worth checking whether your Onan wants a maintained contact or a genuine pulse to start - some of the older marine ones are fussy about that distinction. Mine (static caravan, not marine, so grain of salt) threw a wobbly until I adjusted the pulse duration in the CCGX settings.

Also - and I nearly missed this - there's a separate earth/ground consideration with marine installations that land-based folk like me don't have to worry about. Galvanic isolation can complicate the control wiring.

The Victron documentation covers it but assumes you already know which variant of Onan you're dealing with. What's the model number on yours?

@RetiredEngineer72 is right that the devil's in the details — specifically your relay wiring.

On my static caravan setup with a Quattro 5000, I burnt out the first relay because I hadn't accounted for the inductive kick from the genset's start solenoid. You need a flyback diode across that relay coil, full stop. Victron's documentation glosses over this completely.

Also worth checking:

• Generator start/stop relay type — dry contact only, no voltage from the Quattro side
• Minimum run time — set it sensibly (20 mins minimum) or you'll cycle the genset to death
• Detection input wiring — AC sense from the genset output, not the shore input

What genset control board are you actually running? Onan marine units sometimes have a dedicated two-wire remote start header that plays nicely with this, but the pinout varies by model year.

@FormerMechanic14 nailed the relay point — worth adding that the Quattro's pulse output is only a brief contact closure (configurable but typically 200ms), so if your genset control board expects a sustained signal you'll need a latching relay in between, otherwise it'll just ignore the pulse entirely.

Learnt this the hard way on my van build with a cheap Chinese diesel generator. Wired it direct, wondered why nothing happened, spent an afternoon swearing at it before reading the ESS assistant documentation properly.

Also check your voltage thresholds in VEConfig — the default "generator start on low SOC" values are often set conservatively low. Most people want the Onan firing up well before you're scraping the bottom of the battery bank.

Victron's own relay assistant documentation is actually decent for once. Read that first, then start wiring.

@GoldenNomad raises the crucial point about the pulse duration — worth flagging that in VE.Configure you can actually adjust the generator start/stop detect settings to account for slower-responding relays or control boards on older units like the Onan.

In my cabin backup setup I had persistent false-start detections until I extended the run detect delay to match the Onan's actual warm-up ramp. The Quattro was interpreting slow AC stabilisation as a failed start and immediately issuing a stop pulse.

Also check your AC input current limit is set conservatively initially — if the Quattro tries to draw too aggressively before the genset is stable, you get that same confused pulse loop.

Victron's generator start/stop manual covers the timing parameters clearly if you haven't already worked through it.