Anyone else struggling to keep the fridge cold on long drives through France?

Been through this exact headache on our last trip down to the Dordogne. We've got a 12v compressor fridge (Dometic CFX35) running off a 200Ah Fogstar lithium setup with 400W of solar on the roof, and even then we had some sketchy moments when we hit a long stretch of overcast weather through the Massif Central.

A few things that seemed to make a difference for us:

• Pre-cooling the fridge overnight on hook-up before we set off — massive help
• Keeping it out of direct sun inside the van (obvious, but easy to forget when you're reorganising)
• Adjusting the temperature setting seasonally rather than just leaving it on the default

What I'm still not 100% sure about is whether our alternator charging is actually keeping up properly on driving days. We've got a basic B2B charger but I wonder if it's undersized. Anyone running a Victron Orion for this sort of extended driving? Curious whether the larger 30A version is worth the premium over the 18A.

Also wondering whether anyone's had success with insulating the fridge compartment itself — I've seen some people use off-cuts of Celotex or similar. Seems like it could make a real difference but don't want to restrict airflow and cause overheating issues.

What's everyone else's experience? Particularly interested if anyone's done multiple summers in southern France and found a reliable setup that just works without constantly watching the battery monitor.

@TrevorRoberts75 classic British engineering logic: buy the fridge, forget the French sun is doing 40°C while your compressor works overtime like it owes someone money 🥵

On my narrowboat I learned the hard way that ambient temperature absolutely destroys your fridge efficiency — insulate the cabinet around it or you're just heating the countryside at your own expense.

Also worth checking your solar charge controller isn't throttling mid-afternoon when panels are hottest (classic Renogy MPPT quirk in high temps). Victron kit handles thermal derating more gracefully in my experience.

400W should be plenty but if that Fogstar bank is sitting at 50% SOC by lunchtime, your fridge is fighting a losing battle before the pain au chocolat even gets warm.

@TrevorRoberts75 not a motorhome setup but had similar grief keeping a Dometic cool in my cabin during last summer's heat. One thing that made a noticeable difference — ambient temperature around the fridge matters enormously. If it's tucked into a poorly ventilated cabinet, the compressor is fighting itself.

Have you checked what clearance you've got around the unit? Even adding a small 12v fan to circulate air behind it dropped my power draw significantly.

Also curious — is your 400W solar actually delivering in practice, or are you seeing losses from partial shading on the roof? What's your Victron MPPT showing for peak output on a full sun day in those conditions?

@TrevorRoberts75 Worth checking where your fridge is actually sitting ventilation-wise. On a hot French motorway run the ambient inside the van can be brutal even with windows cracked, and the CFX35 will work its compressor hard trying to compensate. A few things that helped us on similar trips: pre-chill the fridge overnight before departure rather than asking it to pull down warm contents in the heat, and stick a small 12v fan near the compressor vents if there's any restriction. Also worth keeping an eye on your battery voltage during long drives — if your alternator isn't keeping up with the fridge draw plus everything else, you might be running lower than you think. What's your B2B charger situation like? A decent DC-DC charger makes a real difference to how well the system copes on a driving day.

@TrevorRoberts75 one thing nobody's mentioned yet — check your battery voltage under load during the drive. Compressor fridges like the CFX35 get really inefficient when voltage sags below about 12.2V, and if your B2B charger isn't keeping up with the fridge's draw plus the hot ambient temps pushing the compressor harder, you can end up in a nasty cycle where the fridge works twice as hard for half the result.

I've got a similar Fogstar 200Ah setup in my motorhome and fitted a Victron Orion-Tr Smart 30A B2B — made a massive difference on long runs. Also worth setting your CFX35 fridge to "max" rather than relying on the eco mode; counterintuitively it actually maintains temp more efficiently in extreme heat rather than hunting constantly.

What's your B2B situation currently?

@AndyRobinson raises something worth expanding on — I logged exactly this on my Victron Cerbo last summer crossing the Massif Central in 38°C heat. The BMS on my Fogstar cells was throttling output when internal temps crept up, which starved the compressor mid-cycle. The CFX35 is brutal on startup draw — something like 4-6A spike before settling — and if your battery voltage dips below roughly 11.8V at that moment, the fridge protection circuit throws a wobbly.

What saved me: I set a dedicated low-voltage disconnect at 12.2V on my Victron SmartShunt so the compressor always had clean headroom. Also worth checking your cable run — undersized wire between battery and fridge creates voltage drop that never shows up until you're doing 90km/h on the A20 wondering why your brie is sweating.