MPPT Battery Charge Algorithm not using values configured

Had something almost identical drive me mad last winter with my motorhome setup.

Running a 24V Fogstar Drift LiFePO4 bank and had my Victron SmartSolar MPPT set to 28.8V absorption — but it kept flipping into absorption phase somewhere around 28.1–28.3V instead. Took me ages to work out what was going on.

Couple of things I eventually tracked down:

Temperature compensation — if you've got a VE.Smart network running with a battery temperature sensor, the MPPT will actively adjust charge voltages based on temp. Worth checking whether that's silently nudging your targets down.

BMS override — my Daly BMS was communicating via the VE.Direct port and essentially telling the MPPT to back off before hitting the configured ceiling. The MPPT obeys the BMS signal over your manual settings, which makes sense for protection but isn't obvious when you're staring at VictronConnect wondering why your settings are being ignored.

Also worth checking if you've got DVCC enabled in Venus OS (if you're running a Cerbo or similar). When DVCC is active, charge voltage control moves to the GX device, not the individual MPPT — so the values you've punched into the charger itself become largely decorative.

Have a look under Settings → DVCC and see whether a system-wide charge voltage limit is set lower than your MPPT target.

Anyone else seen this with non-Victron BMS units? Curious whether it's purely a communication protocol thing or something else going on at the hardware level.

@DorsetDweller — classic symptom of the MPPT reading a different battery voltage than what the BMS is actually seeing. Check whether you've got VE.Direct or VE.Bus connected to a Cerbo or any other GX device, because if there's a shared voltage sense being pushed from another device on the network, it will override your locally-configured absorption voltage target.

Also worth checking: if your Fogstar's BMS is communicating via any external means and pulling the charge voltage down via DVCC (Distributed Voltage and Current Control) in VenusOS — that'll silently cap your absorption setpoint regardless of what you've typed into VictronConnect.

Had exactly this on my garden office system. Took me an embarrassing amount of time to realise DVCC was capping charge voltage at 27.6V from the BMS side. Disable DVCC temporarily and retest.

@DorsetDweller had exactly this with my garden office setup — Victron SmartSolar kept ignoring my absorption voltage and I was losing my mind.

Turned out I had network mode enabled and the MPPT was deferring to the Multiplus rather than its own stored values. Soon as I set it back to standalone it behaved perfectly.

Worth checking in VictronConnect whether your MPPT is operating as a "networked" device — if it's picking up a shared voltage sense from somewhere else on the VE.Smart network, it'll override whatever you've typed in manually.

Also double-check your battery temperature sensor if you're running one. Low temps were knocking my absorption voltage down automatically via the temp compensation curve — totally forgot I'd set that up 😅

Has anyone checked whether the Adaptive Charging setting is interfering here? On my van build I found the MPPT was silently overriding my manual voltage settings because adaptive mode was still enabled — it recalculates absorption based on previous charge cycles.

Worth going into VictronConnect → your MPPT → settings and confirming "Adaptive absorption" is actually toggled off. Caught me out completely when I first commissioned my setup.

Also — what cable run length are you dealing with between MPPT and battery? Even modest voltage drop across poorly rated cable can make the controller think it's hit target voltage before the cells genuinely have.