RossD said:Easy button? Winter camping. I'll see myself out.
Beat me to it
I have the 12 Volt ARB Elements and it is awesome. Runs for a good while on my starting battery. I supplement it with a 125 watt solar panel and a Victron controller and I can go indefinitely. I try to use some good strategy and that helps a ton.
I will cool it down in the garage before I load it, plug it in for at least 48 hours before I wanna go anywhere. Also pre-fill it my stuff once its cool. Things like steak that freeze fine I will take frozen, two reasons it gives you an extra margin of safety and its a free block of cold. Can always pull them out and thaw them.
Then just some decent strategy. If you are gonna toss a bunch of beer into it, do it when you have bright sun or are going for a drive. If you have shade or its night, minimize the amount you open it.
When I am in bright sun my 125 watt solar panel makes more juice than my fridge uses so at that point cooling stuff down is free.
With our fridge, it's a proper compressor fridge, power draw is very reasonable for the size and capabilities, It's 62 litres.
AVERAGE POWER USAGE AT 32ºC (measured over a 24 hour period)
When we first got it we ran it off the primary battery in the Forester because we'd be driving 3-6 hours a day and only doing overnight stops. It was workable and we never left ourselves with a flat battery or had the fridge cut out (it has adjustable low voltage protection), but relying on your primary battery isn't the best idea and constantly drawing it down like that will shorten its life.
Since then we've put in an auxiliary battery, a 95ah deep cycle battery, and have it linked to the primary battery via a vsr (voltage sensing relay) so as soon as the car shuts off and you have less than 13.8v it open circuits leaving your starting battery isolated from your auxiliary. The vsr also has an option to fit an override switch, which in the event of a flat starting battery, will allow you to use your auxiliary battery like an onboard jump pack.
For charging, along with the alternator, we have a foldable solar panel with a reasonable extension lead.
If you end up going with a 12v thing, I might suggest a solenoid-controlled second battery. I have done this before.
RVs with their own battery use what is usually called an isolator, which is a fancy term for a regulated power supply with a solenoid. It has three main functions; provide battery charging when plugged into shore power, provide 12v power to any DC things you have in the coach, (converter to make power in case the battery is missing or toast) and isolates the coach battery from the vehicle battery. This way you can drain the RV battery and still start the vehicle (and charge the coach battery once it detects a certain voltage threshold.)
You don't need anything that fancy. You would need a continuous-use solenoid and a switch. You can get as complex as you want. I had mine on a DPDT toggle switch (on-off-on). The one side I wired to accessory power, the other to hot power. Switch in the middle meant the two batteries were always separated. Switch up meant they were always connected. Switch down meant they were only connected when the key was on (which is where it stayed most of the time). That switch-down meant that I could drain the RV battery, then when I started the car, it charged both. The nice side effect of adding the DPDT switch was that if I ever accidentally drained the CAR battery, one flip of the switch and it was a built-in jumpstart.
It's a bit of wiring to make it happen, but not bad. You already have the wiring going to the camper, it just needs a coach battery and a solenoid.
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