Mutliplus compact wont start

Right, this one hits close to home because my 12/2000/80 did something similar a couple of winters back — just sat there completely dead one morning, no lights, nothing. Absolute brick.

Turned out the internal fuse on the DC input side had given up the ghost. Worth pulling the unit and checking that first before you start catastrophising about the board itself. On older units like ours, that fuse can corrode or simply fail after years of charge cycling, especially if you've had any high-draw events.

Few things I'd work through in order:

• DC fuse on the unit itself — not just your battery fuse, the one inside the Multiplus casing
• Battery voltage under load — a degraded battery can read fine on a meter but collapse the moment the inverter tries to wake up
• DC cable connections — corrosion on the lugs is absolutely rampant on anything installed pre-2020 in damp environments

The VE.Configure tool (via the MK3-USB interface, which you'd need to borrow or buy) can sometimes reveal fault history even if the unit appears completely dead, if you can get it to communicate at all.

One thing worth noting — Victron UK's warranty support through dealers like Bimble or Merlin is actually decent. If yours is genuinely dead and you can't trace it, some dealers will bench-test for a reasonable fee rather than just quoting you a full replacement.

Anyone else had a silent death on an older Compact? Curious whether this is becoming a pattern on the early units.

@AZY_Marine classic case of "it's not dead, it's just sulking" — check your remote on/off terminals first, because a floating or accidentally grounded pin 1 on the RJ45 will kill it stone dead with zero indication.

Also worth pulling the VE.Bus RJ45 completely out and powering on bare — I've seen daisy-chained cables induce a phantom state that locks the unit out entirely.

If you've got a Victron VE.Configure setup or a GX device, connect via VE.Bus and see if the unit even handshakes — tells you immediately whether it's firmware, config, or hardware.

Final thing: measure DC voltage at the inverter terminals themselves, not at the battery — poor crimps on 70mm² cable can drop enough volts under load (or even standby draw) to trigger low-voltage lockout.

@AZY_Marine worth checking the DC fuse on the Multiplus itself — there's a blade-type fuse on the board that's separate from your main battery fuse, and it's a surprisingly common failure point that leaves the unit looking completely brain-dead. Victron's own documentation buries this rather thoroughly, which is helpful of nobody.

Also, what's the battery voltage actually reading at the Multiplus terminals under load, not at the battery? I've seen 50cm of undersized cable cause enough voltage drop to trigger low-voltage lockout — the unit shuts down and sits there looking guilty whilst the battery is perfectly happy. My garden office setup taught me that lesson the expensive way. What cable cross-section are you running?

@TracyAllen good shout on the internal fuse, caught me out on the narrowboat once — also worth checking the DC cable connections at the battery end, because a loose lug that looks tight will rob you of enough voltage under load to make the whole unit play dead like a possum.

@AZY_Marine had almost the same with my setup on the boat — completely dead, no response whatsoever. One thing nobody's mentioned yet: check the battery voltage at the Multiplus terminals themselves, not just at the battery. I had a dodgy crimp on the negative that was dropping enough voltage under load to trigger the undervoltage lockout, but showed fine on the multimeter at the battery end. The unit just looked dead.

Also worth checking — has the ambient temperature dropped recently? Mine went into low-temp shutdown once in the bilge over winter. The Victron Connect app (if you've got a MK3-USB dongle) will show any stored fault codes which narrows it down massively.