Strange sound

Been getting something similar with my Multiplus II (5000VA, 48V setup at the static caravan) and it's been driving me a bit mad trying to pin down the cause.

Mine does an occasional sharp relay click — sometimes in clusters, sometimes just a single one — and I initially thought it was the transfer switch doing something odd. Took me a while to realise it correlates pretty heavily with grid fluctuations, especially during stormy weather when the local supply here gets a bit wobbly. The unit seems to be constantly checking whether to hand off between grid and inverter mode, and each decision makes that click.

A few things worth checking if you're seeing the same:

• AC input voltage tolerance — tighten the range in VE.Configure so it's not constantly on the fence about accepting grid input
• ESS assistant settings — specifically the minimum SOC and the "keep batteries charged" mode interaction
• Cloudy days are interesting because if you're solar-dependent, the MPPT output fluctuating could be causing the ESS to constantly reassess load vs. generation

I've also noticed mine does it more when certain appliances cycle on and off — the fridge compressor kicking in seems to be a particular culprit, creates a momentary dip that the unit reacts to.

Have you connected it to VRM portal yet? The event logs are surprisingly useful — you can actually see what the unit thinks it's doing at the moment of each click. Made diagnosing mine considerably less guesswork.

Anyone else found specific settings that calmed this down? Curious whether tightening the AC input range is the usual fix or if there's something else people have tried.

@OldSailor79 the Multiplus II does that relay click when it's switching between grid and inverter mode — totally normal. But if it's happening repeatedly and randomly it could be the AC input voltage fluctuating just enough to trigger the transfer relay back and forth.

Worth checking your AC input sensitivity settings in VictronConnect. There's a "wide" setting that makes it more tolerant of dodgy grid voltage — sorted a similar issue on my cabin setup. Mine was clicking constantly until I loosened those tolerances.

Also check the grid frequency isn't wobbling — some rural supplies in the UK are a bit sketchy on that front.

@GlenWard is right about the transfer relay, but worth noting the Multiplus II actually has a spec'd transfer time of around 20ms — fast enough that most kit won't even blink. If @OldSailor79 is hearing it frequently though, that suggests something else is going on.

Could be the unit hunting between modes if your AC input voltage is marginal — caravans on hook-up can be notoriously wobbly. Worth checking the AC Input voltage range settings in VEConfigure; tightening or loosening those thresholds can stop it toggling unnecessarily.

Also — and I learned this the hard way with my own garden office setup — check whether "PowerAssist" is enabled. If it's kicking in repeatedly because your hook-up current limit is set too low, you'll hear that relay working overtime. What's your input current limit set to currently?

Hey @OldSailor79, just to add to what @GlenWard and @TracyAllen have already covered — if you're hearing it repeatedly in a short space of time rather than just occasionally, that can sometimes point to your grid supply voltage fluctuating around the threshold where the unit keeps switching back and forth. Worth having a look in VEConfigure (or VictronConnect if you're using that) at your AC input voltage range settings. Widening the tolerance slightly can stop it flip-flopping. Also check your shore power connection at the caravan — a slightly dodgy hookup cable or corroded connector can cause just enough voltage drop to trigger it. Had exactly that at my plot last winter and it was a right faff to track down!

@YorkshireExplorer makes a good point about repeated clicking being the tell-tale sign something's off.

I had a similar saga on my narrowboat last winter — turned out my grid connection was wobbling just enough to trigger the transfer relay over and over. The Multiplus II is quite sensitive to input voltage fluctuations by default.

Worth checking in VictronConnect (or Venus OS if you've got a GX device) whether your AC input voltage is hovering near the threshold. You can actually adjust the AC input low/high voltage limits in the settings to give it a bit more tolerance before it decides to cut over to inverter mode.

Saved me weeks of head-scratching, that did.