Multiplus II remains disconnected after grid fail

Interesting timing on this thread — I've been chasing something very similar with my Multiplus II 3000 setup on the narrowboat.

Mine's a slightly different config (no AC coupling, just Fogstar Drift lithium and a Cerbo GX), but I've noticed that after a shore power disconnect — whether deliberate or a genuine supply drop — there's sometimes a noticeable delay before the unit picks up inverting duties. Most of the time it's fine, but occasionally it just... sits there. The Cerbo shows the grid as gone but the inverter stays in a kind of limbo state rather than switching over immediately.

A few things I've already checked:

• Transfer switch delay — adjusted in VEConfig, currently at the default 50ms
• Grid code settings — set to G98 (UK), wondering if this is too cautious for my situation
• AC input current limit — doesn't seem relevant here but checked anyway

My suspicion is it might be related to the grid code frequency/voltage tolerances being overly sensitive, causing it to detect a "fault" rather than a clean disconnect, which perhaps changes how it recovers?

Has anyone else in a UK setup had this with G98 or G99 configured? I'm particularly curious whether switching to a less restrictive grid code (for off-grid / backup use where you're not actually exporting) resolves it.

Also — does anyone know if this behaviour changed in recent firmware? I'm on v502 on the Multiplus II.

Would be good to hear from anyone running AC-coupled setups too, as the original scenario sounds like the Huawei inverter might be complicating the handoff further.

@MasterProject the Fogstar Drift + Multiplus II combo is basically the narrowboat dream team, until it isn't 😅

Worth checking your Low DC Restart voltage in VictronConnect — if it's set too conservatively, the Multiplus can sulk and refuse to reconnect even after the batteries have recovered sufficiently. Had exactly this on my boat last winter, sitting there wondering why a perfectly healthy bank was being ignored.

Also double-check your AC Input Current Limit isn't set to zero somewhere — had that bite me after a firmware update wiped a setting.

The Grid tab is the one most people forget exists until it's already ruined their weekend.

@MasterProject check your grid code settings in VEConfigure — UK grid requires G98/G99 compliance and if the Multiplus thinks the returning grid voltage or frequency is outside tolerance (even briefly), it'll sit there sulking for the full reconnection delay before attempting to sync.

Also worth checking: AC Input current limit isn't set suspiciously low, which can cause the unit to refuse the grid rather than admit it's struggling.

On a narrowboat specifically, your shore power hookup quality matters enormously — a dodgy connector introducing resistance will skew the voltage reading the Multiplus sees vs. reality.

Run a data log via VRM during the next grid return event; the AC input voltage graph will tell you immediately whether it's a settings issue or an actual power quality problem at the pontoon.

@OldSailor makes a good point on the grid code side — worth adding that the transfer switch relay can also be the culprit here. Mine did something similar after a grid blip and I found the relay had latched in the wrong state. You can check this in VictronConnect under the advanced settings — there's a relay status readout that'll tell you whether it's actually attempting to reconnect or sitting idle.

Also worth asking: what's your AC input current limit set to? If it's too low and the grid came back at an awkward moment, the Multiplus can sometimes just... refuse to handshake properly. Had this on my motorhome setup before I sorted the settings properly.

What firmware version are you running? Some earlier builds had reconnection quirks that were patched.

@OldSailor and @BevJackson64 have covered the grid code and relay angles well, so I'll add one thing that caught me out on my shepherd's hut Multiplus II — the AC input current limit set too low can cause the unit to effectively reject the grid even after reconnection. Check in VEConfigure under Inverter/Charger → AC Input — if your shore power or grid supply has any wobble on voltage during reconnection, and your input limit is already marginal, it'll just sit there looking sullen and unresponsive.

Also worth confirming: what's your transfer switch delay set to? Default is 3 minutes post grid-restore before it reconnects (G98 compliance window). That trips people up constantly — they assume it's faulty when it's actually just waiting out its mandatory hold-off period.