Anyone else finding their MPPT drops out on cold mornings before the panels even warm up?

Running a Victron SmartSolar 100/30 with two 200W panels in series (open circuit around 48V) feeding a 200Ah lithium (LiFePO4) pack from a Chinese brand — BMS rated to -10°C but I keep mine in an insulated box in the van anyway. Setup's been solid all summer but now we're heading into autumn I'm noticing the controller just... doesn't connect first thing. Blue LED flashes a bit, then nothing for 20–30 minutes after sunrise.

Checked the VictronConnect app and it's logging "no solar" until maybe 8:30–9am even on clear days. Panel voltage looks fine when I probe it manually — sitting around 42V open circuit in weak morning light. Battery's fully healthy, resting at 13.4V overnight. I've updated the firmware and double-checked my absorption/float settings aren't doing anything weird.

Wondering if this is a known cold-weather quirk with the SmartSolar range, or whether my panel VOC is creeping up in the cold and tripping some internal protection? Panels are rated 37.8V VOC at STC so in theory I've got headroom, but I know temperature coefficients can push that higher when it's genuinely cold. Has anyone else seen this on similar kit, or found a fix?

@MarshSoul yeah this caught me out last winter too. Cold panels can spike Voc well above their rated spec — I've seen my 200W Renogy panels hit nearly 52V on a frosty morning before the cells warm up. If your array Voc is already close to your MPPT's input limit at STC, you're probably tripping the overvoltage protection temporarily.

Worth checking your actual cold-morning Voc with a multimeter before the MPPT connects. Victron's MPPT calculator lets you plug in your minimum expected temp to see worst-case voltage.

Also — is your BMS cutting out or is it the MPPT itself? Two different problems. The Victron app should show what's triggering the dropout in the history tab.

@MarshSoul worth checking your actual cold-weather Voc calculation. Panel Voc increases roughly 0.3–0.45% per °C below STC (25°C). Two 200W panels in series at, say, -5°C on a crisp morning could easily push 52–54V depending on your specific panels' temperature coefficient. That's getting uncomfortably close to the SmartSolar 100/30's absolute maximum input.

The MPPT may be protecting itself by refusing to start rather than risking over-voltage damage — which is actually the correct behaviour.

Pull the Voc spec from your panel datasheet, find the temperature coefficient (Pmax or Voc column), and run the numbers for your coldest expected ambient. On my own boat setup I deliberately derate the string voltage calculation to stay 10% below the controller's rated maximum.

If you're consistently nudging that ceiling, rewiring to parallel rather than series would halve your Voc immediately.

@MarshSoul there's another piece to this puzzle worth considering — cold mornings can also mean your LiFePO4 BMS is throttling or outright refusing charge until the cells climb above a threshold temperature (often around 0–5°C depending on the BMS). So even if your MPPT is behaving perfectly, the battery just refuses the current, the MPPT sees a fault condition, and drops out.

I had exactly this with my Fogstar Drift 100Ah last January. Fitted a small self-regulating heat mat inside the battery box, wired through a cheap temperature controller set to kick in below 5°C. Problem vanished almost immediately.

Worth logging what the SmartSolar app actually reports at dropout — protection active versus an overvoltage fault tells you whether it's the battery or the panel Voc issue @DougPearce mentioned.

@MarshSoul had this exact issue on my boat last January. Turned out my SmartSolar was seeing panel voltage spike well above what the MPPT algorithm expected at startup, and it was just bailing out until things stabilised.

Fixed it by enabling the "slow start" option in the VictronConnect app — gives the controller time to properly track rather than throwing an error and dropping out.

Also worth checking: if your BMS is cutting off briefly on cold mornings (what @SolarJo is hinting at), the MPPT sees that as a fault condition and resets. Can create a frustrating loop.

Check your MPPT history in VictronConnect — it logs error codes so you can see whether it's a voltage issue or a load-side disconnect causing the dropout.

Good point from @JasonMoore — I hit something similar in my van build last winter parked up on a Welsh hillside at around -8°C.

What nobody's mentioned yet: check your MPPT's absorption and float voltage settings against your BMS charge parameters. If there's a mismatch, some BMS units will disconnect the load side momentarily during that first cold-morning charge surge, which looks like the MPPT dropping out but is actually the battery side refusing the charge.

I caught mine doing exactly this with a Fogstar battery — Victron's VictronConnect app showed the controller cycling through bulk repeatedly rather than progressing. Adjusted the charge profile to match Fogstar's cold-weather spec sheet and it settled right down.

Worth logging via the app overnight to see when the dropout happens relative to the charge stage transitions.

@MarshSoul one thing worth checking that nobody's mentioned yet — have a look at your absorption and float voltage settings in VictronConnect. If they're set for a generic lithium profile rather than your specific pack's recommendations, the MPPT might be terminating charge cycles early when it thinks the battery is full but actually isn't. Cold batteries also have higher internal resistance, so they'll hit the absorption voltage threshold faster than expected, which can make the controller look like it's dropping out when it's actually just cycling through charge stages oddly. Worth grabbing the BMS specs from your Chinese brand's documentation and matching the charge parameters precisely. Also, are you seeing any fault codes in the Victron app history when this happens?

@MarshSoul worth adding — cold panels produce higher voltage than spec, not lower. Two 200W panels in series on a frosty morning could be pushing your Voc well above that 48V figure. The SmartSolar 100/30 input limit is 100V, so check your actual cold-morning Voc with a meter before dismissing that as the culprit.

In my static caravan setup I derate my string calculations assuming -10°C worst case using the temperature coefficient from the panel datasheet. Victron's MPPT calculator handles this automatically if you plug the numbers in.

@MarshSoul one thing I'd look at is your MPPT's low temperature voltage compensation, if it's enabled. On cold mornings your battery's resting voltage will sit higher than usual, and if the controller thinks it's already at absorption, it won't bother tracking. Worth connecting via the VictronConnect app and watching the live data during that first morning startup — you'll quickly see whether it's briefly registering bulk, absorption, or just floating off entirely. The SmartSolar logs are genuinely useful for this. What charge profile are you running — one of the preset lithium ones or custom?

@MarshSoul one thing worth mentioning alongside what @IanPearce56 said about cold voltage spikes — check your MPPT's input voltage log if Victron Connect allows it. If the combined Voc is nudging close to the 100V input limit on a particularly cold morning, the controller may be protecting itself rather than anything being genuinely faulty. Worth running the numbers with a temperature correction factor applied. There's a good calculator on Victron's site. If you're borderline, it might explain intermittent dropouts rather than a consistent fault pattern.

What nobody's mentioned yet — if your BMS is cutting out first (even briefly), the Victron will see that as a load disconnect and throw a wobbly, so you end up chasing an MPPT fault that's actually a battery protection event. Check your Victron app's history tab for any "battery voltage too low" or "BMS lockout" entries from those cold mornings. My Fogstar Drift did exactly this last January until I tweaked the low-temp charge cutoff settings. The MPPT was innocent the whole time, bless it.

@MarshSoul worth checking your absorption voltage setting in VictronConnect — on a cold morning your panels can push higher open-circuit voltage than the MPPT expects, and if your absorption target is set a touch high for LiFePO4 it can cause odd behaviour when the BMS is already being cautious. Most LiFePO4 wants no more than 14.2V (or 28.4V for 24V systems). Also, what's your battery temperature showing in the app when it drops out? That'd help narrow down whether it's a panel-side or battery-side trigger.

@MarshSoul had exactly this on my narrowboat last February — turns out my Fogstar 200Ah was throttling charge acceptance below 5°C and the Victron was essentially arguing with the BMS like two stubborn blokes over a parking space, both convinced they were right.

@MariaJones interesting you mention the Fogstar throttling — I saw something similar on mine last winter. Worth checking in VictronConnect whether you've got low temperature charge disconnect enabled; if your BMS is reporting cell temps to the Victron via the Smart Battery Sense or a BMV, it can deliberately back off charge current before you've even noticed anything's wrong. On the boat I now keep a small reptile heat mat under the battery box on overnight freeze warnings — crude but effective. Doesn't take much to keep the cells above the threshold.

@MarshSoul one thing I haven't seen mentioned yet — have you checked whether your SmartSolar is set to the correct battery preset? If it's defaulted to a generic lithium profile rather than one matched to your specific BMS limits, the charge algorithm can behave oddly at low temperatures even when the BMS itself hasn't triggered. Also worth enabling the low temperature cutoff in VictronConnect if your battery supports it via a BMS cable or smart shunt — that way Victron handles the cold protection rather than relying solely on the BMS reacting after the fact.