Anyone else running a Victron MultiPlus in passthrough mode on a narrowboat?

Been running a Victron MultiPlus 12/3000/120 on my narrowboat for about 18 months now. Mostly it's on battery/solar, but when I'm on a marina mooring I run it in passthrough (shore power straight through, inverter on standby). Works brilliantly — seamless switching when I disconnect and cruise off.

My question is around power assist. I've got a fairly weedy 10A shore supply on my current mooring and occasionally I'm running the kettle, induction hob, and battery charger simultaneously. The MultiPlus is supposed to kick in and assist from the batteries when shore demand exceeds the input limit I've set. In theory it should be transparent. In practice I sometimes get a brief flicker on my 12V lighting circuit at the moment it cuts in — nothing trips, just a half-second dimming.

Has anyone else seen this? I've got my input current limit set to 8A in VictronConnect to protect the mooring supply, and my batteries are 200Ah Fogstar Drift LiFePO4. Wondering if it's a comms lag between the MultiPlus and the BMS, or just normal behaviour during the assist transition. Happy to share my VE.Configure settings if it helps diagnose.

Running passthrough on my van's MultiPlus and honestly it's like having a butler who silently judges your electricity consumption — works flawlessly but the Victron app will absolutely grass you up to yourself at 2am when you've left the kettle on standby.

@BordersOffGrid yeah same setup on my boat! MultiPlus is brilliant for this honestly. One thing I'd flag — keep an eye on your transfer switch relay if you're frequently plugging/unplugging shore power. Mine started clicking a bit oddly after about two years of marina living, turned out fine but gave me a mild panic 😅

Also worth checking your shore power inlet is a proper 16A blue commando socket rated for marine use — I bodged mine initially with a cheaper option and the Victron kept throwing low voltage warnings because of resistance in the connection.

What're you running for batteries? I'm on Fogstar Drift LiFePO4s and the passthrough + charge profile combo works a treat once you've got the absorption/float voltages dialled in properly.

Not a narrowboat setup here — static caravan and garden office — but I run a MultiPlus-II 24/3000 and passthrough has been rock solid for the caravan when we're on a site with hook-up.

One thing worth mentioning that I haven't seen flagged yet: if you're switching between passthrough and inverter mode a lot, keep an eye on your transfer switch relay over time. Victron's are rated for a decent number of cycles but on a boat with variable shore power availability, you could be clocking up a fair few. Worth occasionally checking in VictronConnect that your transfer times look normal — any sluggishness there can be an early indicator.

Also, have you got a Cerbo GX logging your shore power quality? Marina supplies can be surprisingly dirty and it's useful data to have.

@BordersOffGrid interesting thread — I'm running a MultiPlus-II 24/5000 primarily for EV charging integration, so passthrough mode gets used quite heavily when grid-tied.

One thing worth flagging that nobody's mentioned: check your transfer switch relay rating against your actual passthrough load. The 12/3000 has a 120A transfer relay, which sounds generous, but sustained high loads close to that ceiling will cause relay wear over time. Victron's own documentation recommends keeping continuous passthrough below ~80% of rated relay capacity.

Also worth setting the shore current limit in VictronConnect accurately — if it's too high, your marina shore power breaker will trip rather than the MultiPlus throttling back gracefully. For narrowboat 16A shore supplies specifically, I'd set it to 14A to give yourself headroom.

The ESS assistant rather than plain passthrough is worth investigating if you want seamless solar injection during marina stays.

Great thread! One thing worth mentioning that nobody's touched on yet — if you're on a marina with a dodgy or weak shore power supply, the MultiPlus's PowerControl feature is genuinely brilliant. You can set a shore current limit so it won't trip the marina's breaker, and it'll automatically top up from batteries if your loads spike above that threshold. Really useful when marinas have those frustratingly low 6A or 10A pedestals.

Also worth checking your transfer switch relay occasionally — on a boat there's more vibration than a static install and it's just good practice. @BordersOffGrid eighteen months in sounds like yours is performing well though, which is reassuring!