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

Been having a proper nightmare with my Victron SmartSolar 100/30 this past fortnight. Temperatures here in Yorkshire have been dropping to around -5°C overnight and I keep waking up to find the controller has lost its Bluetooth connection to the VictronConnect app — sometimes it's just showing the last cached data from hours ago. The panels themselves (two 200W monos wired in series, so around 44V Voc) seem fine, and the batteries are charging okay once the sun gets going, but that lost connection is doing my head in.

I've tried reinstalling the app, forgetting and re-pairing the device, even a firmware update last week (now on v3.14). Made no difference. The weird thing is it only seems to happen when it's been below freezing overnight — once the temperature climbs back above about 4 or 5°C during the day, the Bluetooth kicks back in without me touching anything.

Has anyone else seen this with Victron kit specifically, or is it a wider Bluetooth-in-the-cold thing? The controller is mounted inside my shed (uninsulated, timber framed), so it's not getting rained on but it's definitely seeing those low temperatures. Wondering if it's worth adding a bit of insulation around the controller or whether there's a firmware/settings fix I'm missing.

@WattRoger had the exact same bother with my 75/15 a couple of winters back. Turned out the Bluetooth module was the culprit rather than the MPPT itself — connection dropping doesn't necessarily mean the unit's misbehaving, just that the BT radio gets flaky in the cold.

Worth checking a few things:

• VictronConnect app — is the controller still actually charging properly, or genuinely offline?
• Check your battery cable connections — cold causes metal to contract and loose terminals are a nightmare
• Try a firmware update if you haven't already

My unit was still doing its job fine, just couldn't talk to my phone about it. Actual MPPT function carried on regardless.

If it's genuinely dropping charge cycles though, that's a different issue — might be worth posting your battery voltage logs.

Good shout from @FormerMechanic74 on the Bluetooth angle. One thing worth checking that hasn't been mentioned - have a look at your battery temperature compensation settings in the VictronConnect app. At -5°C your lead-acid batteries (assuming that's what you're running) will need a noticeably higher absorption voltage than in summer, and if the controller thinks something's wrong with the charge profile it can sometimes behave oddly.

Also worth checking your cable connections at the battery terminals - cold weather causes contraction and I've seen perfectly good crimps become intermittent just from thermal cycling over a few winters. A dab of petroleum jelly on the terminals wouldn't go amiss either.

What firmware version are you running on the SmartSolar? Victron pushed out a few fixes last year that addressed some cold-weather stability issues. Might be worth updating if you haven't recently.

Great thread, this. @WattRoger I'd add something nobody's touched on yet - check your battery temperature sensor if you've got one fitted. Mine was giving duff readings in the cold which caused the SmartSolar to drop into a protection mode and essentially disconnect itself whilst logging it as a comms fault. Dead confusing until I figured it out.

Also worth having a look at your cable connections at the battery terminals. Cold weather causes contraction and I've seen perfectly good crimps work loose enough to cause intermittent dropouts that look like controller issues but aren't. A bit of dielectric grease on the terminals before winter is something I do religiously now.

What firmware version are you running? Victron pushed an update last year that addressed some cold weather stability issues - definitely worth checking you're current via VictronConnect.

Been through something similar on my boat last winter — brutal when you're relying on it for heating. One thing nobody's mentioned yet: check your battery temperature sensor if you've got one fitted. Mine was giving duff readings in the cold which caused the MPPT to throttle back charging thinking the batteries were warmer than they were.

Also worth checking the VE.Direct cable connection if you're monitoring via a Cerbo or similar — those connectors can develop high resistance in cold conditions and cause the controller to drop off the network entirely.

In the VictronConnect app, look at your history data — if you're seeing lots of "absorption" phases cutting short, that's usually a temperature compensation issue rather than a Bluetooth fault.