Another AC disconnect query for the Multiplus-ii GX

Been scratching my head over something similar with my narrowboat setup and wondered if anyone else has wrestled with this.

Running a Multiplus-II GX with a 48V Fogstar Drift lithium bank and a SmartSolar 150/35 — all AC loads on the AC-out-1 side. The idea being that when shore power is available at a marina, it passthrough charges the batteries and handles loads, then seamlessly switches to inverter when I disconnect.

What I can't quite nail down is the AC disconnect behaviour when grid input drops out. Specifically:

• Does the MP-II GX actually break the AC input connection cleanly before switching to inverter mode, or is there a brief blip that resets sensitive electronics?
• I've got a small NAS running for chart data and it's rebooting occasionally when I leave marina power — feels like it's catching that transfer gap

I've had a dig through the Victron documentation and the VEConfigure settings, and I've played with the UPS function toggle but I'm not entirely sure that's the right lever to pull here.

Is this a grid code / country settings issue? I'm set to the UK grid profile — could that be adding a mandatory delay before reconnect/disconnect that's causing the blip?

Anyone running a similar semi-grid-tied arrangement on a boat or shepherd's hut with shore power who's found a clean solution? Particularly interested if you've used ESS Assistant versus standalone Inverter/Charger mode — not sure which route makes more sense for occasional marina hookups rather than a permanent grid connection.

@DerekMoore89 narrowboat with a Fogstar Drift bank — practically identical to my own setup, so this rings very loud bells indeed.

The AC disconnect on the Multiplus-II GX is almost certainly your ESS Assistant getting twitchy about grid voltage tolerances. Pop into VEConfig and check your AC Input Current Limit — if it's set too conservatively, the unit throws a tantrum and disconnects like a sulky teenager.

Also worth checking:

• Grid code settings — G98/G99 compliance thresholds can be surprisingly aggressive
• Your AC input voltage range in the ESS Assistant itself (I widened mine to 180–265V and the phantom disconnects vanished)

The Fogstar Drift BMS comms are solid, so I'd rule that out first and focus purely on the AC side. What firmware version are you running? Anything pre-3.13 on Venus OS had some genuinely odd disconnect behaviour.

@DerekMoore89 your post seems to have got cut off — we're missing the actual question! Assuming it's about the AC input disconnect behaviour on the Multiplus-II GX with lithium, the usual culprit is the Low DC Disconnect threshold in VEConfigure clashing with the BMS comms over the VE.Bus.

On my garden office setup I had the Multiplus cutting shore power unexpectedly because the assistant's "sustain" voltage was set too conservatively for the Fogstar Drift's charge profile. Worth checking your ESS Assistant settings specifically — the Minimum SOC and DC input low shutdown values need to match what the Fogstar BMS is actually reporting via DVCC.

Are you running DVCC enabled with the BMS in control, or manual charge parameters? That distinction changes everything about how the Multiplus handles disconnect decisions.

@DerekMoore89 yes your post definitely got clipped — we're missing the key part of the question.

While you sort that, I'll mention I've been looking at similar AC disconnect behaviour on my motorhome Multiplus-II GX setup. A few things worth clarifying when you repost:

• Are you seeing the disconnect on AC input or AC output?
• What firmware version are you running on the GX?
• Have you set your AC input current limit in VictronConnect or via the CCGX interface?

The Fogstar Drift's BMS comms with the Multiplus can sometimes influence how the unit responds to grid presence — worth knowing whether you've got that CANbus link configured properly too.

@DerekMoore89 classic narrowboat internet connection cutting off mid-thought — the canals are trying to protect us from our own wiring decisions.

@DerekMoore89 mate, that's the narrowboat canal gods telling you something. I've got a similar rig on my boat — Multiplus-II GX, Fogstar Drift 48V bank, the works. Spent three weekends last autumn debugging AC disconnect behaviour while moored somewhere near Braunston with absolutely no signal.

Whatever the actual question turns out to be, I'd wager it involves either:

• AC input current limit getting confused when shore power is dodgy
• The ESS assistant doing unexpected things when the grid drops
• Or battery protection kicking in and the Multiplus throwing a wobbler

Post the full question when you're back in civilisation and I can probably point you at the relevant VEConfigure setting. There's usually a very specific checkbox buried three menus deep that sorts it. Always is.