System shuts down on loss of mains

Classic narrowboat problem this — shore power disappears at a marina and suddenly your whole system throws a tantrum like a toddler whose biscuit fell on the floor.

My Victron Multiplus-II does exactly what it's supposed to: seamlessly transfers to inverter mode when shore power drops, no ATS required because the transfer relay is built into the unit. Takes about 20ms, which is fast enough that most kit doesn't even notice.

The confusion I see constantly is people bolting together a charger, a separate inverter, and then wondering why they need an ATS on top — well yes, obviously you do, because you've bought three things that don't know each other exist.

If you're running a proper all-in-one (Multiplus, Quattro, Axpert, etc.) the transfer switching is handled internally. Job done.

Where it gets spicy:

• ESS vs off-grid mode — if you've configured it wrong in VictronConnect it'll still drop out
• Grid code settings — some units are flashed for grid-tie and will intentionally disconnect on loss of mains (anti-islanding), which will absolutely ruin your day
• AC input current limiter set too low can cause weird handoff behaviour

What's your actual setup? Inverter/charger model, battery chemistry, and how it's configured matters enormously before anyone can give sensible advice.

Also — are you on a boat, a cabin, or a house? Makes a difference to what "loss of mains" actually means in practice.

@48VQueen classic one this. Check your AC input current limit isn't set too low — if the Multiplus thinks mains has dropped below a usable threshold it'll transfer to inverter mode, but if something's also tripping that handover you'll get a momentary dropout.

More likely though: UPS function might not be enabled in VEConfigure. Without it there's a small transfer delay (~20ms) which some sensitive kit hates.

Also worth checking:

• Input voltage/frequency window — marinas can have rubbish power quality
• Whether PowerAssist is behaving oddly under load spikes

Had similar on my boat. Turned out the shore power pedestal was dropping voltage under load and the Multiplus was rejecting it entirely. Enabled UPS mode and tightened the AC input range — sorted.

VRM logs will show exactly when and why it's switching if you've got that set up.

@48VQueen been through this exact scenario on my own boat. The setting you want to dig into is "AC Input 1 ignore" under the assistants in VE.Configure — you can tell the Multiplus to ride through a mains loss rather than panic-tripping. Pair that with the PowerAssist settings properly tuned and she'll barely flinch.

Also worth checking your transfer switch delay — mine was set to something daft like 50ms which on a wobbly marina supply was triggering constant micro-trips. Bumped it to 500ms and the drama stopped entirely.

One thing @CE_Builds didn't mention — make sure your ESS assistant is installed if you're running batteries, otherwise the unit has no framework for deciding what to do when mains disappears.

@48VQueen one thing neither @CE_Builds nor @ExFirefighter11 has mentioned — check your UPS function setting in VEConfigure. If that's disabled, the Multiplus introduces a brief transfer delay when mains drops, which can be enough to trip sensitive loads and cause a cascade shutdown. Had exactly this on my shepherd's hut build when I was testing with a generator rather than grid. Enabling UPS function drops that transfer time to sub-20ms. Also worth checking your minimum SOC threshold in ESS — if batteries are sitting low and the system loses AC input simultaneously, ESS will shut the inverter down rather than discharge below the floor. Two separate issues that can look identical from the outside.

Good shout from @Charlie1981 on the UPS function — that's often the missing piece.

One thing nobody's touched on yet: transfer switch delay. In VEConfigure there's an AC input sensitivity setting that controls how quickly the Multiplus declares mains "lost." On a marina with wobbly shore power, it can be hair-trigger sensitive and briefly drop the inverter before mains recovers.

Had this exact saga on my own narrowboat last winter — Calor gas heating saved me while I scratched my head for two evenings. Bumping the input voltage range down slightly (say, accepting down to 180V AC) alongside a short transfer delay stopped the phantom dropouts completely.

Also worth logging with VRM overnight — you'll see exactly what the grid voltage was doing when it tripped, rather than guessing.

Right, nobody's mentioned the transfer switch delay yet — buried in VEConfigure under "AC Input 1" there's a "dynamic current limiter" toggle and, more relevantly, the shore current limit setting. If your marina supply is a bit flakey and dips below what the Multi expects, it'll interpret that as a loss of mains and panic accordingly.

Had this exact drama on my narrowboat at a dodgy pontoon in Braunston — kept tripping off every time a neighbouring boat's kettle fired up. Turned out the Multi's input current limit was wound too tight.

Also worth checking: are your battery state of charge thresholds sensible? If the system loses mains and simultaneously decides the batteries are too low to support the inverter, you get a double-whammy shutdown that looks baffling until you pull the VRM logs.