MP II: Safety Timeout (low voltage) when comms lost: Make Optional, default to internal voltage

Been thinking about this a lot lately, especially as I'm planning an upgrade on my tiny house setup.

Currently running an MP II 48/5000 with a Cerbo GX and a couple of Victron SmartSolar MPPTs, with a JK BMS handling my Fogstar DIY cells over CAN.

Here's what's nagging at me — if the CAN comms drop between the BMS and the Cerbo (which does happen, even briefly), the MP II can trigger a safety timeout and shut down based on lost communication rather than actual battery voltage. Depending on timing, that could cause a completely unnecessary outage even when the cells are absolutely fine.

Surely the logical fallback should be: if comms are lost, revert to the inverter's own internal voltage measurement rather than going straight to a protective shutdown? That seems like a far safer and more graceful degradation than pulling the plug entirely.

Some questions for those who've dug into this:

• Has anyone managed to configure something like this in VEConfigure or via MQTT/Node-RED workarounds?
• Is this a known limitation of the CAN-based BMS integration, or am I missing a setting somewhere?
• Would this behaviour change with the MP II 48/6000 (thinking of upgrading anyway)?

I get why Victron defaults to a cautious shutdown — better than overcharging or deep discharging — but making it optional with internal voltage as the fallback just seems sensible, especially for those of us running well-configured BMS units we actually trust.

Anyone else hit this scenario or found a workaround?

@PaddyGibson this hits close to home — had exactly this scenario play out on the boat last winter. Left her moored for three weeks, Cerbo lost comms with the BMS overnight, MP II went into protective shutdown, and came back to a completely dead domestic bank.

The frustration is real. Victron's logic makes sense on paper — "comms lost, assume the worst" — but the internal voltage measurement is perfectly capable of holding the fort temporarily.

What I'd love to see is a configurable comms-loss grace period with fallback to internal voltage thresholds. Even 30 minutes would've saved my bank. Fogstar Drift cells don't love sitting at zero.

Essentially: make the paranoid behaviour the opt-in, not the default. Most of us with established systems know our kit well enough to make that call.

Hey @PaddyGibson, solid point and I can see why it's frustrating. The MP II is perfectly capable of protecting itself using its own internal voltage sensing — it did exactly that before BMS comms became the norm.

What I'd love to see is a configurable fallback hierarchy: primary = BMS comms, secondary = DVCC voltage, tertiary = internal sensing, with user-defined thresholds for each level. That way you're not left with a binary "comms or nothing" situation.

@VDH_Boats your boat scenario is exactly why this matters — unattended systems in remote or marine environments need graceful degradation, not hard shutdowns that leave you without power for days.

Have you raised this on the Victron Community forum directly? Their dev team do occasionally pick up feature requests there, especially when there's a clear safety rationale behind them.

Good shout @PaddyGibson. The frustrating thing is Victron almost got this right — the MP II's internal voltage sensing is perfectly solid without the Cerbo in the loop.

Worth flagging: you can set a low battery shutdown voltage directly in VEConfigure that acts independently of any DVCC/BMS comms. It's not a perfect substitute but it means the inverter won't just blunder on into the cells if the Cerbo drops off.

That said, I agree the current behaviour — where comms loss triggers an immediate safety timeout rather than graceful fallback to internal sensing — feels like the wrong default. Fine for a managed commercial install, but for small off-grid setups it's a real liability.

Raised something similar with my Fogstar/Victron stack. Would love to see this as a configurable option in a future firmware update rather than needing a workaround.

The Ducato's had this exact drama play out twice now — once when a dodgy RJ45 decided to go on holiday mid-winter, and the MP II dutifully shut everything down including the diesel heater controls. Woke up to a very cold van and a very unhappy wife.

What baffles me is that Victron clearly trust the internal voltage sensing for the assistant logic and battery monitor, yet the moment comms drop it's apparently useless for protection. Pick a lane, lads.

@VDH_Boats leaving a boat unattended with this behaviour genuinely worries me — frozen pipes are no joke. At minimum there should be a "comms timeout action" dropdown in VictronConnect: protect via internal sensing vs shutdown. Default it to internal sensing and let the paranoid among us choose shutdown.

My Fogstar Drift cells have better self-preservation instincts than the MP II's fallback logic — and they don't even have a Cerbo.