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

Mine's in a garden office rather than a van but I've had similar gripes with Renogy's MPPT controllers when temps drop. Noticed it gets a bit hesitant to start harvesting in the mornings — takes longer than it should to wake up and start tracking properly.

Switched over to a Victron SmartSolar a while back and the difference in cold-morning behaviour was pretty noticeable. Victron just gets on with it from the off, even when we had that nasty cold snap back in January.

Few things worth checking if you're sticking with the Renogy though:

• Make sure your battery temperature compensation is set correctly — Renogy's defaults can be a bit aggressive in cold temps
• Check the firmware version, there were some reported issues with earlier versions affecting cold-start behaviour
• Worth logging the data if yours has BT — helps spot if it's genuinely erratic or just slow

Not saying Renogy is terrible, plenty of folk get on fine with them. But their customer support is a bit hit-and-miss if you do need to raise it.

Anyone running them alongside a Fogstar lithium setup? Curious whether the BMS interaction makes any difference to how the controller behaves when it's cold.

FrankFisher | 847 posts

@WattHamish Yeah, classic cold-morning sluggishness with these units. Worth checking whether you've got temperature compensation enabled and whether the sensor's actually reading correctly — mine was giving daft readings because the probe had worked loose from the battery terminal. Also, Renogy's default absorption voltage is set a bit conservatively from the factory, which compounds the issue in winter when the controller's itself cold and processing slowly.

One thing that genuinely helped me was mounting mine inside rather than on an external wall — ambient temperature makes a surprising difference to how snappily it wakes up. What are your morning temps like in the office? Below about 5°C and they do seem to take an age to get going properly.

AnneOliver | 203 posts

Ooh this is timely — I've got the same controller running my garden office setup and yes, it's been driving me absolutely mad this winter. Mine sometimes won't properly kick in until nearly 9am on cold mornings, which given we're already losing daylight hours feels like a genuine waste.

Quick question for the group though: has anyone tried adjusting the absorption voltage settings to see if that helps coax it into life earlier? I've been wondering whether it's actually a temp compensation issue rather than the controller being genuinely sluggish. My Fogstar lithium cells are presumably fine in the cold but maybe the Renogy is being overly cautious?

Also — does anyone know if Renogy's newer firmware addresses this at all? I can never find a straight answer on their support pages. 🙄

ExFarmer90 | 1,204 posts

Had exactly this on my setup last winter — shed-based office with a Renogy 40A running four 200W panels. What fixed it for me was relocating the controller away from the exterior wall. Mine was basically sitting in the same ambient temp as outside, and these units really do prefer somewhere between 10–25°C to wake up properly.

Also worth checking your battery voltage settings — I found mine had defaulted to a profile that was slightly off for my Fogstar LiFePO4s, and the controller was basically second-guessing itself every cold morning before committing to bulk charge.

@AnneOliver — what battery chemistry are you running? That makes a big difference to how the Renogy interprets those early low-voltage morning readings when everything's cold and sluggish.

DodgyCaptain | 312 posts

Different application here — running a Victron SmartSolar on the narrowboat — but cold morning sluggishness was an issue until I moved the controller inside the cabin rather than in the engine bay. Temperature makes a massive difference to how these units behave at startup.

Worth checking whether your Renogy is mounted somewhere exposed to the cold itself, rather than just the panels being cold. Controller ambient temp can affect how aggressively it sweeps for MPP first thing.

Is there any data logging on yours @WattHamish? Even the basic Renogy app should show you what time it actually starts pulling current versus when there's presumably usable voltage on the panels. That gap tells you a lot about whether it's a controller issue or just marginal morning irradiance.