Protezione batteria e carico da malfunzionamento MPPT dello smart solar

Been pondering something similar lately with the setup aboard Perseverance (my 58ft trad stern, currently moored somewhere between a duck and a bad decision on the Kennet & Avon).

I've got a Victron SmartSolar MPPT 100/30 feeding a pair of Fogstar Drift 100Ah LiFePO4s, and it occurred to me recently — what actually happens to the load side if the MPPT decides to have a wobble? A rogue voltage spike, a firmware hiccup, the usual Victron-induced existential crisis at 2am.

The question I keep circling back to is whether a Victron BatteryProtect between the battery and the loads is genuinely sufficient as a failsafe, or whether I'm creating a false sense of security. The BP will happily disconnect under low-voltage conditions, but it's not exactly designed to catch over-voltage events coming from a misbehaving charger upstream, is it.

Worth noting the BatteryProtect's own manual specifically says not to use it on the charge input side — which some folks seem to discover after the magic smoke escapes.

Has anyone actually had an MPPT malfunction badly enough to damage downstream kit? I've read the theory, but real-world narrowboat or off-grid horror stories (ideally with a happy ending and minimal weeping over ruined inverters) would be very welcome.

Also curious whether anyone's using a proper BMS with load disconnect as the primary protection rather than bolting a BP onto a system as an afterthought — seems like the more elegant solution but I'd love to hear how it's working in practice.

@ExmoorNomad — the K&A, brave soul.

Had exactly this scenario on my own boat last summer. The concern with MPPT runaway isn't just overcharge — it's the rate of rise. A BMS will disconnect on overvoltage, but if your MPPT keeps pushing after isolation, you can get some interesting voltage spikes on the DC bus that'll take out anything sensitive downstream.

What I run now: Victron SmartSolar into a Cerbo GX, with the BMS DVCC signal looped properly so the MPPT gets told to back off before the BMS needs to hard-disconnect. Belt and braces.

The key is not relying on the BMS as your primary protection — treat it as the last resort, not the plan.

What cells are you running? LiFePO4 or something more excitable?

@ExmoorNomad the thread title's in Italian which is either very cosmopolitan of you or autocorrect has gone rogue again 😄

Worth adding: your Victron SmartSolar MPPT has a configurable absorption voltage ceiling and maximum charge current limit baked into VictronConnect — if those are set correctly for your battery chemistry, a genuine runaway scenario is actually quite rare. The BMS on your batteries (assuming lithium?) is your last line of defence, and it should hard-disconnect before anything dramatic happens.

What's more likely to cause grief on a narrowboat is a dodgy temperature sensor giving the MPPT bad compensation data, nudging absorption voltage higher than intended over time. Check your temp sensor connection regularly — canal vibration is brutal on connectors.

What battery bank are you running on Perseverance? That'll determine whether this is a theoretical concern or something worth actually engineering around.

@ExmoorNomad the Italian title is sending me 😂

On the actual question — Victron's own BMS talking to the MPPT via VE.Direct is your best belt-and-braces. If the BMS trips, it pulls the charge enable signal and the MPPT backs off cleanly rather than just getting disconnected under load (which is when you risk voltage spikes killing your gear).

Secondary to that, a decent fuse sized correctly between MPPT and battery — people underestimate this one. Fogstar cells are tough but they're not bulletproof.

On a narrowboat specifically, space is tight so the all-Victron ecosystem actually earns its premium — everything talks to everything. Mixed brands you're bodging it with relay workarounds.

What BMS are you currently running?

@TracyAllen @MarineGaz the title is going to haunt him for weeks, that.

On the actual substance — the BMS-to-MPPT communication is only half the story. What protects you when that link fails silently? Had a moment on the cabin build where a VE.Direct cable worked loose and the MPPT just carried on regardless, no fault flagged anywhere obvious.

The answer I landed on was a dedicated battery protect on the load side and making sure the BMS had hard-disconnect capability — not just a polite request to the MPPT to back off. Victron's own SmartSolar will respect a remote H port signal, but you want belt and braces.

What BMS are you actually running on Perseverance? That changes the answer considerably.