Anyone else's MPPT throwing a wobbly in sub-zero temps?

Woke up on the boat this morning to -4°C and my Victron SmartSolar 100/30 had basically gone into a sulk — showing 0W input despite the panels being frost-free and hitting decent sun by 9am. Took a good hour before it started playing ball again.

Running two 200W Renogy mono panels into a 200Ah Fogstar Drift LiFePO4 bank. Setup works an absolute treat in summer but winter's turning it into a part-time job.

Anyone know if this is just normal cold-weather sluggishness on the Victron, or is there a setting I'm missing in VictronConnect? Wondering if the battery BMS cutting off due to cold temp protection is confusing the controller into thinking there's nowhere to send the juice.

HappyBodger | 847 posts | ⚡ Solar Nerd

@BoatMark Classic cold-morning behaviour on the SmartSolars, especially on a boat where the battery bank gets properly chilled overnight. The MPPT is likely seeing a very high internal resistance on your batteries and throttling right back to protect them — it's not actually broken, just being cautious.

Worth checking your battery temperature compensation settings in the VictronConnect app. If you've got a Smart Battery Sense or a temp sensor fitted, make sure it's actually reading correctly.

Also — what battery chemistry are you running? AGM and lead-acid get very grumpy below zero and genuinely need a gentler charge profile until they warm up a bit. Lithium at sub-zero is a whole other conversation and can be more serious.

Usually sorts itself out once the bank warms up mid-morning. Did it recover by say 10-11am?

Chalky54 | 1,203 posts | 🔋 Off-grid since 2019

@BoatMark Worth checking your absorption voltage settings — in very cold conditions the battery voltage can sit unexpectedly high overnight, and the controller sometimes gets confused thinking it's already fully charged when it wakes up. Had exactly this on my narrowboat last February.

Also, have a look at the VictronConnect app history — there's often a telling error code logged that doesn't show on the display itself. Mine turned out to be a high voltage fault that cleared itself once things warmed up a bit.

One thing that genuinely helped me was enabling the "battery temperature sensor" compensation if you're not already using one. Makes a noticeable difference to how the controller behaves in these cold snaps. The Victron SmartSense dongle is reasonably priced and worth every penny on a boat.

BazLewis72 | 312 posts | ☀️ Solar Tinkerer

@BoatMark Had almost identical with my 75/15 last February on a narrowboat. One thing nobody's mentioned yet — check whether the controller itself is physically cold. If it's mounted somewhere uninsulated, the unit's own temperature sensor can throttle output dramatically until the internals warm up. I moved mine inside the battery compartment where it stays a few degrees above ambient and the problem basically vanished. Also worth a look in the VictronConnect app under the history tab — see if it's logging any protection events overnight that might give you a clue what triggered it. What's your battery type set to in the controller?

EwanLamb | 521 posts | 🏕️ Van & Cabin Dweller

@BoatMark One thing nobody's mentioned yet — have you checked whether the controller itself got cold enough to trigger thermal protection? The SmartSolar units can throttle right back if the internal temperature drops too low, separate from any battery or panel issue. If your controller is mounted somewhere exposed on the boat rather than inside a relatively sheltered spot, that could be your culprit.

Also worth connecting via the VictronConnect app and checking the error history — it'll log exactly what caused the shutdown overnight. Should tell you straight away whether it was an overvoltage situation (common in cold weather as @Chalky54 hints at) or something else entirely.

Mine did something similar last winter in the van until I relocated the controller away from an external wall. Made a noticeable difference.

NotAnElectrician80 | 847 posts | 🏚️ Static Caravan Survivor

@BoatMark My Victron SmartSolar does the exact same dramatic performance every January in the caravan — turns out the battery temp was so low it was throttling charge current to avoid damage, which is the MPPT doing its job rather than having a breakdown, unlike me at 7am in -5°C trying to diagnose it in my dressing gown. Check your low temp cut-off setting in VictronConnect — if you're running lithium (Fogstar or otherwise) that setting matters enormously. AGM is more forgiving but still strops below about 0°C. The Victron documentation actually covers this reasonably well for once, buried about 47 menus deep obviously.