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

Not on a motorhome, but I've got a pair of Renogy 40A MPPTs running on my narrowboat and I've noticed something similar through the winter months.

On really cold mornings — we're talking sub-5°C — mine will occasionally show a brief fault code before sorting itself out within a few minutes of the panels warming up. I chalked it up to the voltage spike you can get from cold crystalline panels pushing close to the charge controller's VOC limit. Worth checking your panel array's cold-weather VOC calculation if you haven't already, because that catches people out more than they realise.

That said, mine have been mostly reliable. I charge an EV from the boat setup via a Victron MultiPlus arrangement, so I'm pushing these controllers fairly hard and they've not completely let me down yet.

A few things worth trying:

• Update the firmware if yours is on an older version — Renogy quietly pushed a stability fix last year
• Check your cable connections at the controller terminals; cold contraction can loosen things slightly
• Review your temperature compensation settings — running the stock defaults in a UK winter isn't always ideal

I did briefly consider swapping to a Victron SmartSolar 100/30 on one of the channels, mostly for the Bluetooth monitoring rather than any dissatisfaction, but haven't pulled the trigger yet.

Curious whether yours is doing it consistently or just occasionally — and what panel wattage you're running into it? Might help narrow it down. Others on here will have more motorhome-specific experience than me, so hopefully someone chimes in.

@CarlWalker what's it actually doing? "Flaky" covers a lot of ground — are we talking slow to start tracking, voltage spikes, dropping out mid-session, or something else entirely?

I've got a Victron SmartSolar on the boat and cold mornings are actually better for panel output in my experience — lower cell temps, higher Voc. If anything mine's greedier at dawn in January than August.

That said, I've heard Renogy's cold-weather compensation can be a bit hit-and-miss. Worth checking your battery temperature compensation settings if you're running AGM or lithium — incorrect coefficients will cause odd behaviour when temps drop sharply overnight.

Also, are your panels seeing any frost shadow or partial shading first thing? That'll mess with MPPT tracking more than the temperature itself.

Mine does the same on frosty mornings in the motorhome — I just assume it's having a lie-in like the rest of us.

@ExBrickie raises the right question.

Had similar grief with a Renogy 40A on the shepherd's hut last winter. Turned out the unit was struggling to establish comms with the battery bank below about 3°C — Renogy's firmware seems to have some quirk where it sits in a boot loop rather than just cracking on.

Fixed mine by insulating the controller's mounting location better. It's mounted inside but on an external wall, which was the problem. Moved it to a warmer spot and haven't had issues since.

Worth checking whether it's actually the MPPT or your battery BMS throwing a low-temp charge lockout though — easy to blame the wrong component. If you've got LiFePO4 without heating, that's almost certainly your culprit rather than the Renogy itself.

Not a motorhome setup either — garden office here — but I had something similar with my Renogy 40A last February. What fixed it for me was checking the battery temperature compensation settings. The controller was defaulting to a fixed absorption voltage rather than adjusting for the cold, which was causing weird behaviour until the ambient warmed up a bit.

Worth checking if your units are set to AGM/sealed vs whatever chemistry you're actually running. Mine was misconfigured out of the box and took months before I bothered digging into the Bluetooth app properly.

Since switching to a Victron SmartSolar I've not had the issue at all — the temperature sensing is just more refined. Renogy isn't bad for the money but the cold-morning edge cases do seem to catch it out. @BodgeItAndScarper's point about settings is probably the right thread to pull on first.