Anyone else's Victron MPPT throwing a fit when temps drop below freezing?

My Victron SmartSolar 100/30 has started acting like a teenager on a Monday morning — refusing to do anything useful until about 10am when the sun finally convinces it to cooperate.

Running 200W of Renogy panels into a Fogstar 12V 100Ah lithium at my cabin in the Peak District, and I reckon the low-temp cutoff is triggering but I'm not 100% sure if that's the MPPT or the BMS throwing a paddy.

Anyone managed to sort this with the temperature compensation settings in VictronConnect, or am I just doomed to warm the battery up manually like some kind of cave dweller?

NigeScott98 | 47 posts

@WayneTaylor Ha, the "teenager on a Monday morning" description is spot on — I had exactly this with my 100/20 last winter!

Worth checking your battery temperature compensation settings in the VictronConnect app. If your batteries are sitting below freezing, the MPPT will deliberately throttle charging to protect them — which is actually correct behaviour rather than a fault.

If you haven't got a Smart Battery Sense or temperature sensor fitted, the controller is essentially flying blind and defaulting to cautious behaviour. Adding one made a noticeable difference for me.

Also double-check your absorption voltage isn't set too low for cold conditions. AGM and gel batteries need higher voltages in winter.

What battery chemistry are you running? That'd help narrow it down a bit.

Pylontech_Wizard | 203 posts

@WayneTaylor Check your low temp cutoff settings in VictronConnect — it's probably doing exactly what it's supposed to do tbh. Lithium cells genuinely don't want charging below freezing, so the MPPT backs off.

My static van setup does the same through winter. I just live with it rather than fight it.

If you want earlier morning charging, a battery heat mat is the proper fix — some folk wire them to a small relay triggered by the BMS. Bit of faff but works a treat.

Also worth checking your absorption/float voltages are set correctly for whatever battery chemistry you're running. Wrong profile can make the whole thing look broken when it isn't.

What batteries are you on? Makes a difference to the advice.

Curly38 | 312 posts

@WayneTaylor Yeah the low temp cutoff is the obvious culprit as @Pylontech_Wizard says, but also worth checking your battery voltage first thing in the morning. If it's dipped low overnight the MPPT won't kick in properly until panels generate enough to clear the threshold.

Had this exact faff with my cabin setup last January. Fogstar lithium, 100/30, same symptoms. Turned out my cable runs were slightly undersized and voltage drop in the cold was tipping it over the edge.

Few things to verify:

• Battery temp sensor actually connected?
• BMS comms working via VE.Smart networking?
• Any error codes showing in VictronConnect history?

The history tab in VictronConnect is your mate here — it'll show exactly when it cut out and why. Victron are good like that, at least.

SunnyFisher | 89 posts

Had almost identical grief on the narrowboat last winter — except mine was doing it at 9am so slightly less lazy than yours 😄

One thing nobody's mentioned yet: check whether your battery temperature sensor is actually reading correctly. Mine had worked itself loose from the battery terminal and was basically just measuring the ambient air temp inside the cabin instead. Victron was seeing -3°C when the batteries were actually a perfectly reasonable 8°C, and throwing a wobbly accordingly.

Worth checking in VictronConnect — if the temp reading looks suspiciously low compared to reality, that's your culprit before you start fiddling with cutoff thresholds.

Soggy condensation on the sensor connection can cause weird readings too if your setup is anywhere near as damp as a narrowboat bilge... 🚢

Compo89 | 89 posts

@WayneTaylor One thing nobody's mentioned yet — check whether your battery temperature sensor is actually reading correctly. I had a similar situation last winter and it turned out my BMS temp sensor was giving the MPPT a false low reading because of where it was positioned (mine was stuck right against the cold cell casing rather than between cells). The MPPT was seeing -4°C when the actual cell chemistry was closer to 2°C. Moved the sensor, problem largely sorted. Also worth insulating your battery box if you haven't already — even a bit of closed-cell foam makes a surprising difference overnight. A frozen battery genuinely doesn't want charging though, so some morning delay is actually the controller doing its job properly rather than being awkward about it.

Paul1975 | 647 posts

@WayneTaylor Worth checking your VictronConnect app and having a look at the battery voltage at the point it's refusing to charge. If the resting voltage looks artificially low first thing in the morning, that's often the battery BMS being a bit stroppy in the cold rather than the MPPT itself being the problem.

Also — and this catches people out — make sure your absorption and float voltages are set correctly for cold weather. Some folk set these up in summer and forget that colder cells actually need slightly higher charge voltages to reach the same state of charge. The Victron manual has a temperature compensation figure (typically around -16mV/°C for a 12V lead-acid system).

What battery chemistry are you running? Makes a big difference to how you'd approach this.

CumbrianWanderer | 203 posts

@WayneTaylor This is exactly what happened with my shepherd's hut setup two winters back. The culprit for me wasn't the MPPT itself — it was the absorption voltage being set slightly too high, which combined with cold-thick battery chemistry made the controller basically give up and restart the charge cycle repeatedly.

Worth pulling up your VictronConnect history graph and seeing if you're getting those repeated bulk→absorption→float→bulk loops in the early morning hours. Mine was doing it like clockwork below -2°C.

Also — what batteries are you running? If they're Fogstar lithium, the low-temp cutoff on the BMS might be the actual villain here.

CrispyTrekker | 312 posts

@WayneTaylor Worth looking at your Low Temperature Cut-off setting in VictronConnect — if you're running lithium (even LiFePO4), the MPPT will protect the battery by refusing to charge below a threshold you may not have deliberately set. Default is often 5°C.

Also check whether your BMS is disconnecting the charge input independently. In my motorhome last January I had the MPPT behaving identically — turned out the Fogstar battery's internal BMS was cutting charge before the Victron even got involved.

Two separate protection layers can compound each other and make diagnosis confusing.

RobWebb59 | 1,847 posts

@WayneTaylor One thing nobody's mentioned yet — have you got your battery type set correctly in VictronConnect? If it's on the default AGM profile but you're running lithiums, the charge algorithm will behave oddly in cold weather. Also worth checking whether your battery BMS itself is cutting charge early due to low cell temps — the MPPT might actually be responding correctly to a signal from the BMS rather than throwing a wobbly on its own. Disconnect and reconnect via Bluetooth and check the "history" tab for any protection events overnight.