Reading out multiple temperature sense

Been down a similar rabbit hole recently while wiring up my shepherd's hut build, so this feels timely.

I've got a Victron Multiplus-II 3kVA paired with a Fogstar Drift 200Ah, and I started wondering whether the temp sense input is actually being wasted if your BMS is already handling battery thermal protection independently. The Drift's BMS does its own thing, so the Multiplus temp sense could theoretically be repurposed — monitoring ambient inside the hut rather than sitting on the battery terminal.

The snag I keep running into is that the Victron temp sense is calibrated expecting a specific NTC thermistor characteristic, so if you move the sensor away from the battery and into free air, you're still only reading one point. What I'd really want is:

• Battery temperature (via BMS/Cerbo GTS probe)
• Inverter compartment temp
• Ambient room temp

The Cerbo GX with its dedicated temperature sensor inputs is obviously the cleaner solution here — you can log multiple probes through VRM and set alerts. But not everyone wants to spec a full Cerbo just to get a couple of extra temperature channels.

Has anyone actually experimented with using the Multiplus temp sense for ambient rather than battery, and compensated charge curves manually? I'm curious whether the charge voltage offset behaves sensibly when the sensor isn't thermally coupled to the cells at all — could cause overcharge issues if ambient swings wildly in an uninsulated space.

Also worth noting for anyone running a van conversion in this group — underbody battery temps can diverge massively from cab ambient in winter, so getting this right genuinely matters rather than just being a nice-to-have.

Interested to hear what others have done.

@Bomber78 the Fogstar Drift's internal BMS already handles cell-level temperature monitoring and will signal the Multiplus-II to back off via the VE.Bus BMS comms if things get spicy. So you're not flying blind there.

Where it gets interesting is ambient temperature — particularly if your shepherd's hut sees proper Welsh winter nights. My cabin setup runs a separate Victron Temperature Sensor wired directly to the MPPT, which adjusts charge voltage accordingly. The Multiplus can also take a battery temperature input through the VE.Smart network if you've got a BMV-712 or SmartShunt in the mix.

One physical sensor, shared intelligently across the whole Victron ecosystem via Bluetooth — no rats' nest of wiring. That's the bit most people miss when they start bolting on extra sensors unnecessarily.

Same setup in my shepherd's hut actually — Multiplus-II with a Drift 200Ah.

One thing worth adding: the Drift communicates over Victron's VE.Bus/CAN path, so GX device users (I've got a Cerbo GX) can see the battery's reported temps on the dashboard without any extra sensors. Saved me bothering with separate probe wiring.

That said, I did add a cheap Victron Temperature Sensor near the battery compartment floor anyway — ambient readings can differ quite a bit from what the BMS reports internally, especially in a hut that gets properly cold overnight. Worth having both data points if you're running through winter.

@Fiona1974 snap — shepherd's hut twins, except mine probably has more thermal drama given it's basically a tin can on wheels that goes from "arctic tundra" to "Sahara sauna" between November and July.

One thing nobody's mentioned: if you're paranoid like me, slap a cheap DS18B20 probe on the outside of the Drift casing and pull it into a Raspberry Pi or similar — gives you a paper trail of ambient temps which is dead useful for warranty arguments if anything ever goes pear-shaped with Fogstar support.

@PikeGazer the tin can thermal drama is real — I've got a similar situation with my EV charging setup where ambient swings massively affect cell behaviour.

One thing nobody's mentioned yet: if you want independent temperature logging beyond what the BMS reports over COMMS, a cheap DS18B20 sensor wired into a Venus OS device (Raspberry Pi or Cerbo GX) lets you pull cell surface temps into VRM alongside the BMS data. You can then set custom alarms in Venus OS if temps diverge unexpectedly — useful for catching bad connections or uneven thermal distribution that the internal BMS might not flag until it's already throttling.

Victron's DVCC framework will still defer to the BMS protection limits, but having that supplementary data visible in VRM dashboards gives you a much clearer picture of what's actually happening inside the box during charge cycles.