Originally Posted by Pooneil
IME, running on 12V will draw down the battery, even when hitched to a running TV. So either install a battery cut off switch or run on gas. The fridge should cool quite well on gas and that is what I do. Some people fret (with reason) about using gas while driving because of having a flame around the gasoline pump when filling up. So its your call.
The tow vehicle wiring will have a lot to do with whether or not the fridge will run well on DC while being towed, AND how well the camper battery(s) will charge while being towed.
If 16 gauge wiring is used for the tow vehicle battery charge wire and the ground wire, 10 amps can usually flow without excessive voltage drop. Once the voltage at the camper battery drops below about 13 volts, the fridge will continue to cool, but the camper battery will not recharge or will recharge very slowly. If the voltage drops below 12.5, the camper battery will start supplying power to the fridge, discharging itself. These voltages can be verified with the tow vehicle running, and the fridge on DC.
Ideally, the tow vehicle wiring harness should be even heavier (10 gauge to 14 gauge) to allow faster recharge of the battery while keeping the fridge running. Keep in mind, camper running lights (tail and marker) on will add significantly to the current load running through the ground wire.
Max current for wire sizes to keep voltage drops reasonable (and the camper battery charging):
16 gauge - 10 amps
14 gauge - 15 amps
12 gauge - 20 amps
10 gauge - 30 amps
The fridge on my A122 draws 6 amps on DC. I haven't measured the tail and marker lights, but I'm guessing another 4 amps when they are on (assumes non-LED). Doesn't leave a lot for battery charging unless your harness has big wires. This is also why a tow vehicle is a slow way to recharge a deeply discharged camper battery.
Because of past experience with difficulties keeping fridges running on propane when being towed at altitude (we seldom camp below 6000ft), I do run the fridge on DC while towing. I am careful to turn off the fridge before I disconnect the tow vehicle when setting up. I have seen PUPs at campgrounds with batteries discharged to nothing in a few hours when the fridge was forgotten and left on DC.
I pre-cool the fridge at home and fully charge the camper batteries on AC the night before a camping trip.
When I lived in the East, turning propane on and off for the tunnels and ferries became too much trouble, and I shifted to 12V only when towing.
just my experiences
2014 Rockwood A122 with 2 size 24 batteries
2008 Hyundai Entourage (minivan)