Anyone else had issues with MPPT controllers dropping out in cold weather?

Noticed something odd with my Victron SmartSolar 100/30 over the past few weeks during the cold snap we've had. Running four 100W panels in two parallel strings feeding into a 200Ah LiFePO4 bank, and the controller keeps dropping to float then back to bulk randomly throughout the day, even when there's decent sun. Temperatures here in the Peak District have been sitting around -3 to 2°C most mornings.

Done a bit of digging and I wonder if the issue is the Voc on the panels climbing higher than usual in the cold — at -3°C my panels should theoretically be pushing well over their rated 22V open circuit, which on two strings in parallel should still be fine for the 100V input limit, but I'm wondering if there are brief spikes tripping something. The VictronConnect app logs are showing input voltage jumping around quite a bit before the dropouts happen.

Has anyone else seen this behaviour with Victron MPPT units specifically, or is this something more likely to be a dodgy MC4 connector reacting badly to the temperature cycling? I've already re-seated all the connectors on the roof but it's still happening. Keen to hear if anyone's had similar and what actually fixed it.

MistyTrekker | Posts: 847 | Location: Scottish Borders

@DontPanic8 Your post got cut off there, but I think I know where you're heading! I had almost identical behaviour with my SmartSolar 75/15 last January during that brutal cold spell we had up here.

Worth checking your battery temperature compensation settings first — LiFePO4 has quite specific cold-weather charging requirements compared to lead-acid, and the default profiles can sometimes cause the controller to back off or drop out entirely if it thinks it's protecting the cells.

Also, have you checked whether the Victron Connect app is logging any protection events? Mine was throwing up high voltage warnings I'd completely missed. Sometimes it's the panels themselves producing unexpectedly high Voc in very cold conditions, which can trip the controller's input limits.

What temperatures are you seeing overnight roughly?

HelenPhillips | Posts: 1,203 | Location: Array

@DontPanic8 Your post did cut off — but I'll take a stab at what you're seeing. My SmartSolar 150/35 on the shepherd's hut did something similar last January: panels producing voltage but controller sitting in absorption or even float prematurely, or conversely refusing to start the charge cycle at all.

Two things worth checking:

1. Panel Voc in cold — cold significantly raises open-circuit voltage. If your string Voc is creeping close to the 100V input limit at sub-zero temps, the controller will protect itself and drop out.
2. BMS interaction — LiFePO4 BMS units often cut charge acceptance below ~5°C. The Victron then sees a disconnected battery and throws a fault.

Check your VictronConnect history log — it'll timestamp exactly when dropouts occurred versus temperature readings. That data narrows it down fast.

Gazza25 | Posts: 2,156 | Location: Array

Had almost the exact same situation on my narrowboat last January. What I suspect happened — and @DontPanic8's missing text probably confirms this — is the panels were producing voltage way above the expected Voc because cold panels spike hard. My four 175W panels on a crisp morning were pushing nearly 95V into a SmartSolar rated to 100V. Heart was in my mouth.

Worth checking your actual input voltage in the VictorConnect history logs during those cold mornings. The controller may be seeing an over-voltage condition and protecting itself by cutting out entirely.

Quick fix if that's the issue: check your string configuration. Sometimes dropping to a single parallel string rather than series reduces your Voc enough to keep things comfortable. The Victron MPPT calculator accounts for temperature coefficients — genuinely worth running your numbers through it.

BirchLover | Posts: 412 | Location: Array

Yeah the post cut off but guessing you're seeing the MPPT disconnect or behave erratically when temps drop sharply?

Worth checking your LiFePO4 BMS — most cut charging below 0°C to protect the cells. The Victron sees a "load" that suddenly disappears and can look like a controller fault when it's actually the BMS doing its job correctly.

On my shepherd's hut setup I added a small self-regulating heat mat to the battery box, powered overnight from a tiny 20Ah lead-acid buffer. Sorted the winter dropouts completely.

Also check the Victron app history — it logs the exact reason for any disconnection. Makes diagnosis dead easy rather than guessing. If you see "BMS connection lost" or similar that'll point you straight at the culprit.

HamishLee | Posts: 847 | Location: Scottish Highlands

Chiming in from up here where cold weather is basically our default setting! One thing nobody's mentioned yet — check your VOC (open circuit voltage) on those panels in the cold. Low temperatures actually increase panel voltage, sometimes significantly, and if your string voltage is creeping close to the controller's 100V input limit when it's frosty, the MPPT may be protecting itself by shutting down. Worth measuring with a multimeter on a cold morning before the controller connects.

Also worth checking the Victron Connect app logs — the SmartSolar records protection events, so you'll be able to see whether it's an overvoltage shutdown or something else entirely. That'll help narrow it down rather than guessing. What's your panel spec for VOC at STC? Happy to help run the numbers if you share them.

PU_Sparks | Posts: 1,203 | Location: North Yorkshire

Worth checking your battery temperature compensation settings if you haven't already. LiFePO4 has a much flatter voltage curve than lead-acid, and some Victron units can behave oddly if they're still configured with lead-acid charge profiles — the absorption voltage target can look "wrong" to the controller in cold conditions and trigger a protective dropout.

Also, pop into the VictronConnect app and check your BMS communication settings. If you've got a smart BMS talking to the SmartSolar via VE.Direct or Bluetooth and there's any signal instability in the cold, the controller will disconnect as a precaution. Seen this catch people out before.

What temperatures are you actually seeing at the battery and controller? That'd help narrow it down considerably. @HamishLee will probably have strong opinions on cold-weather installs! 😄