How to find out where my CVL/ Setpoint is coming from

Been scratching my head over something similar with my own setup and wondering if anyone's hit the same wall.

I've got a Fogstar Drift lithium pack paired with a Multiplus-II and I keep noticing the charge voltage isn't quite where I'd expect it. I think I've got the CVL set correctly via the BMS DVCC path, but I'm genuinely not 100% sure what's actually winning the argument when there are multiple potential sources all trying to set the charge voltage.

From what I understand, the hierarchy goes something like:

• DVCC + BMS CVL (via VE.Can or VE.Bus BMS)
• ESS assistant settings
• Charger profile set manually in VEConfigure

But which one actually takes precedence in a real system? And how do you confirm which source is actively controlling the setpoint at any given moment?

On a GX device I know you can dig into the DVCC menu and see what's being broadcast, but if the BMS is pushing one voltage and the ESS is pushing another, does Venus OS just pick the lowest? Or is it more complicated than that?

Particularly curious whether anyone running a sodium-ion battery (Natbatt or similar) has dealt with this — they seem to have slightly different CVL requirements and I wonder if the system handles them cleanly.

Is there a reliable way to log or monitor exactly which source is setting the CVL in real time? Remote monitoring makes this even trickier to diagnose when you can't just stand in front of the kit.

@JoeTurner the OP got cut off but I'll take a stab at what you're chasing.

On my cabin setup I spent a week confused about why my Multiplus-II was charging to odd voltages. Turned out CVL was being written by two sources fighting each other — the BMS via CAN and a hardcoded absorption voltage in VEConfig.

Open VictronConnect, go to your Multiplus-II device page, then hit the remote console. Check DVCC settings — if SVS and SCS are ticked and you've got a BMS on the VE.Can bus, that's your authority. The BMS wins.

Run dbus-spy via SSH on the Cerbo if you've got one. Filter for CVL and you'll see exactly which service is writing it and from where. No guessing.

Fogstar Drift should be pushing sensible limits over CAN anyway — what firmware are you on?

Curious whether anyone's checked the VE.Can network as a source? On my setup I found the CVL was being pushed by a DVCC source I'd completely forgotten I'd configured months earlier.

Worth opening VictronConnect and going to the DVCC settings page — there's a line showing "Active source" which tells you exactly what's winning the negotiation. Could be your BMS talking over CAN, could be VE.Smart networking, could be something hardcoded in ESS.

@MountainHermit did you rule out a VE.Smart dongle on the battery side overriding things? I've seen Fogstar setups where a Bluetooth temperature sensor was quietly influencing the setpoint without the owner realising.

What firmware is your Multiplus-II on @JoeTurner? There were some DVCC handling changes around v500 that shifted priority logic noticeably.

@VE_Boats good shout on the CAN bus — that's exactly where I'd look first with a Multiplus-II setup.

Quick way to narrow it down: in VictronConnect or VEConfigure, check whether DVCC is enabled. If it is, that's your likely culprit — the system's pulling CVL from whatever device has the highest priority on the network, usually the BMS if it's talking over CAN.

On my narrowboat I had a similar head-scratcher. Turned out my Fogstar wasn't even properly recognised as the BMS master, so the Multiplus was just defaulting to its own internal charge profile. Messy.

Try the GX device (if you've got a Cerbo or similar) → Settings → DVCC and see what's listed under "Controlling BMS". That'll tell you straight away where the setpoint's actually originating from.

Good thread — had almost this exact puzzle on my boat last year.

Once I'd ruled out VE.Can (as @VE_Boats and @WezFrost suggest), the culprit on mine turned out to be VEConfigure — specifically an old bulk/absorption voltage setting that was quietly overriding everything else. Easy to miss because it doesn't shout about it.

Worth opening VEConfigure and checking the Charger tab directly on the Multiplus-II itself. If your CVL from the BMS is say 55.2V but VEConfigure has 57.6V baked in, the higher value can win depending on your ESS assistant setup.

The GX Device → DVCC screen is your friend here too — it'll show you the active CVL and flag the source if DVCC is properly enabled. On my Fogstar setup that screen made everything suddenly obvious.

Great thread — and something I spent a rather frustrating afternoon untangling on my own narrowboat setup last winter.

Once you've ruled out VE.Can (as others have covered), don't overlook shared voltage sense via VE.Bus. If you've got a Venus device in the mix — GX, Cerbo, whatever — check Device List → your Multiplus → Parameters in VictronConnect or the remote console.

The CVL source is listed explicitly there. It'll tell you whether it's coming from the BMS, the DVCC settings, or a manual override baked into the inverter config itself.

The Fogstar Drift communicates over CANbus, so in theory DVCC should be honouring its CVL rather than your own entered values — but only if DVCC is actually enabled in Venus OS and the BMS is showing as active. Worth a double-check there before anything else.