Why did I have to reboot my Multiplus II

Had a weird one last week at the cabin worth sharing.

Running a 48v Victron Multiplus II with a bank of Fogstar Drift cells. BMS was showing 58% SOC, resting voltage looked healthy — no alarms, nothing obvious. Fired up the genny to top things up after a few cloudy days (classic UK autumn, cheers Scotland) and the Multiplus just... stopped responding. VRM portal went dark, Touch 50 frozen. Hard reboot sorted it but I'm still not entirely sure what triggered it.

My best guess is the BMS briefly cut comms during the generator startup surge, and the Multiplus didn't like that. Could also be a CVT on the genny causing a voltage spike on the AC input — I've not got a clean generator, just an old Honda EU22i.

Few things I'm looking into:

• Whether my DVCC settings in VE.Configure are too aggressive
• Checking the assistant stack — I've got ESS + generator autostart running together which apparently can cause odd interactions
• Logging more granular BMS data via Cerbo GX to catch any micro-disconnects

SOC percentages can also be deceptive if your battery hasn't done a proper full cycle recently — calibration drift is real, especially post-summer when usage patterns change.

Anyone else seen their Multiplus behave strangely on generator input rather than solar? Particularly curious if others with a Cerbo + third-party BMS combo have hit this — feels like a handshake issue rather than anything hardware-related.

RetiredChef26 | 847 posts | ⚡ Solar & Storage Enthusiast

@XU_VanLife Your post got cut off mate, but I think I can guess where this is going!

Had something similar with my Fogstar setup last autumn. The Multiplus can sometimes fall out of sync with the BMS if there's a brief communication dropout over VE.Bus or VE.Direct — even without any visible alarms triggering. The inverter essentially loses its reference point and throws a wobble.

Worth checking your cable connections on the comms side, particularly if the cabin gets cold overnight. I found a slightly loose VE.Direct connector was my culprit. Also have a look in VictronConnect at the error history — it'll often log something even when the front panel shows nothing obvious.

What firmware version are you running on the Multiplus? That might be relevant too.

PhilJackson | 312 posts | 🏡 Tiny House Tinkerer

@XU_VanLife your post also got cut off which is frankly on-brand for a Multiplus II mystery thread 😂

Boycie25 | 1,204 posts | ⚓ Narrowboat & Off-Grid Bodger

@XU_VanLife Post cut off twice now — the forum software is apparently as reliable as my old inverter was. Whilst we wait for the full story, I'll hazard a guess: your BMS pulled the plug via the charge/discharge relay faster than the Multiplus II could gracefully shut down, and it's sulking about it. Classic mismatch between BMS communication speed and inverter response time.

Running Fogstar Drift cells myself on the boat — brilliant cells, but if your BMS protection settings are aggressive and you're not using the Victron DVCC properly over VE.Can or BMS-Can, the Multiplus essentially gets the power equivalent of someone yanking its kettle lead out mid-brew.

Finish your post when the forum decides to behave itself, and tell us what BMS model you're using — that'll narrow it down considerably.

Sam1985 | 203 posts | 🔋 Off-Grid Learner

@XU_VanLife Looks like the forum's eating your posts! Try splitting it into two replies or use the desktop site rather than mobile — that usually sorts it.

Intrigued though, because "BMS showing healthy SOC but needed a Multiplus reboot" sounds familiar. I had something similar last spring — turned out my BMS and the Multiplus had drifted out of sync on the SOC reading, and the Multiplus had actually hit an internal protection threshold the BMS wasn't flagging properly.

Definitely worth sharing the full details when you can get the post through. What firmware are you running on the Multiplus? And are you using DVCC with the BMS communicating over VE.Can or just standalone?