I see this is an old discussions. I get a lot of information from these old threads, though this discussion has stalled. However, I see there is a missing summary of information that I happen to have, so this is for the next person looking at these old threads for information, but not necessarily participating in the discussion.
There are two basic kinds of camper fridges: There are propane combination fridges (some combination of propane, 12v, and 110v), and 12V compressor fridges. Both worth considering for a small camper cost about $500-$1000. Running on 12v, both the propane fridge and the 12v compressor fridges have very different efficiency. NOTE: The inexpensive little 12v coolers are not even worth considering. Also the little 110V dorm fridges are NOT competitively efficient in a camper using a 12v to 110v inverter.
A 2way/3way fridge that uses propane (combination of propane, 110V, 12V) use gas absorption to make it cold. So what. The key is HEAT is what makes the cooling gas flow around the system - like heat from a propane flame. These fridges are meant to run on propane. An internal electric heater that works on 110V or 12V will make the fridge work when the propane flame is not present, but the heat from the electric heater is VERY INEFFICIENT in this configuration. If the 12v mode on a gas absorption fridge is used without a constant charge to the battery, it will drain a camper battery in a few hours. The 12v mode on a gas absorption fridge is basically meant to be used when traveling when the propane is supposed to be shut off (legally in some states, though I have never heard of anyone even being checked), and the vehicle is charging the camper battery, so the fridge won't drain the battery.
Then there are 12v compressor fridges meant to run only on 12v electricity. They are very efficient using electricity. A single 100AH battery (50AH usable) can power a good compressor fridge for about 1.5 days at 90 degrees and over 2-3 days at 70 degrees. Combined with a 135watt solar panel it will run indefinitely charging the battery with 4 hours of full-sun or charging all day on a cloudy-day (not applicable in the winter in northern climates). Less charging times means more battery is needed to run the fridge between charges or more solar panels are needed to charge in less time.
Hopefully this helps keep the discussion straight as some participants are talking about 12v usage on a propane/gas-absorption fridges and some are talking about 12v usage in a compressor fridges -- and some are using information from one type to apply to the other. I learned a lot.
Edited by GeezerMike, 06 February 2016 - 12:03 AM.
