Anyone else finding the Renogy 40A MPPT a bit flaky in cold weather?

Been running one of these in the van since last spring and honestly it was fine all summer — no complaints. Then November hit and I started getting some weird behaviour. Early mornings when it's been a cold night, the controller would just... sit there. Panels clearly getting light, voltage showing on the display, but charge current hovering at basically zero for 20-30 minutes before it'd finally wake up and start pulling properly.

At first I thought it was the panels being shaded or frost-covered, but I'd wipe them down and still get the same issue. Took me a while to narrow it down to the controller itself sitting in an uninsulated section of the van floor — basically running at near-zero temperatures overnight.

Moved it closer to the cab area where it stays a bit warmer and things improved noticeably. Not perfect, but the lag dropped from 30 minutes to maybe 5-10.

Worth noting I've seen people on here swear by their Victron SmartSolar units in all conditions, and I'm starting to see why the price gap exists. That said, the Renogy hasn't failed as such — it just sulks in the cold like a teenager on a Monday morning.

Curious whether anyone else has had this and whether there's a firmware update floating about, because I've heard whispers that Renogy pushed something out. Also wondering if anyone's tried insulating the unit itself — felt a bit daft thinking about wrapping a charge controller in foam but I'm not ruling it out.

What are people running instead if they've ditched the Renogy?

@CrispyMechanic — classic cold-weather MPPT behaviour, and the Renogy units are particularly prone to it.

What you're likely seeing is the controller struggling with the steep voltage spike you get from cold panels at low irradiance. Cold panels can push Voc up 10–15% above their rated spec, and if your array is already near the controller's input ceiling, it throttles aggressively or faults out entirely.

A few things worth checking:

• Bulk absorption voltage — some units default oddly and behave worse when temperatures drop
• PV input voltage at first light — worth logging if you have any way to capture it
• The Renogy's temperature compensation algorithm is fairly crude compared to Victron's; it doesn't always respond quickly enough to rapid morning warm-up

Ran into similar with my cabin array before switching to a Victron SmartSolar — the Bluetooth logging alone made diagnosing these gremlins ten times easier.

Just to add something that might not have been mentioned yet — have you checked your battery temperature compensation settings, @CrispyMechanic? A lot of people overlook this on the Renogy units. When it's cold, your AGM or lithium (whatever you're running) needs a different charge voltage, and if the controller isn't compensating properly it can look like flaky behaviour when it's actually just the controller doing something approximating the right thing, badly.

Also worth checking the firmware version if you haven't already. Renogy did push an update a while back that improved cold-weather tracking on the 40A. Their support is a bit hit and miss but the firmware page on their site is straightforward enough.

What temperatures are we talking roughly? Below freezing or just low single figures?

Swapped mine out for a Victron SmartSolar and suddenly my mornings are less dramatic than a soap opera — coincidence? Probably not.

Hey @CrispyMechanic — worth checking whether the controller is going into a protection mode due to the panel voltage spiking in cold conditions. Cold panels can push Voc noticeably higher than the spec sheet suggests, and if your array is already near the controller's input ceiling in summer, winter mornings could be nudging it over the limit. Have a look at your actual panel Voc at low temperatures using the temperature coefficient in the datasheet — there's a formula for it. If you're borderline, that could explain the flakiness without it necessarily being a fault as such. Might be worth logging the input voltage on startup if your unit supports it. What's your panel configuration?