Originally Posted by fisk
In case anyone cares, it didn't work. I unplugged the AC just before we left. I'm assuming it switched to battery, because the battery was almost dead when we got there two hours later. I had to hook up a battery charger to it for 20 minutes just to raise the roof. If it tried to switch to gas, it couldn't since I had that shut off.
Also, the fridge was not really cold at all. We still had to keep the cold food in a cooler with ice until the next morning.
Since the camper was on AC for several days before we left, and then connected my truck on the two hour drive there, AND still was dead when I got there, do you think it could be a problem with the battery? I was able to charge it and have power to raise the roof within 20 minutes. After being there for about 40 hours (connected to the camp AC), it sounded fine when I was lowering the roof. I realize that was less of a load, but it sounded like it had plenty of power.
This is my take on it. Your fridge will run on 12 V supply but not through the 12 V supply on your tow vehicle to trailer plug connection. Your van battery will not charge either using this connection method unless you drive for about 12 hours a day maybe. The reason for this is called 'voltage drop' The auto wire gauge is way to light to supply the voltage required to charge van battery or run van fridge on 12 V efficiently to keep products cold enough.
What you have to do is either use a DC to DC battery charger to charge your van battery as you drive. That may or may not supply sufficient charge to the battery in the van to run the fridge on 12 V if the fridge is wired to the van battery with heavy cable. I am talking 3 to 5 AWG wire.
A better way to do this process with success is what I have done.
I run two batteries under hood. 12 volt start battery and a 12 volt 100 AMP Deep cycle battery connected with electronic isolator so the aux battery will not discharge the start battery as aux battery discharges. The aux battery will charge once start battery fully charged as you drive.
Next is connecting the Aux battery to the Van battery. The van battery is 100 AMP deep cycle battery. They are connected with 3AWG (25mm2 for me) cable positive and negative run from AUX battery to the rear of vehicle to 175 AMP Anderson plug. An Anderson plug lead to the van battery in same size cables. Use 50AMP to 100AMP fuse at either end of this close to each battery. The alternator will charge Van battery and will charge the Aux battery only when start battery if full.
Wire the fridge 12 volt supply to the van battery and use a fridge switch (RV Electronics - Manufacturer of Breaksafe, Fridge Switch and Water Level Indicator :: FridgeSwitch
to prevent fridge flattening batteries when you are stopped. Use gas for long stops or AC power. Use heavy cable to wire the 12 volt fridge supply from van battery to avoid voltage drop. Voltage drop is the killer of 3 way fridge not running as it should. It will only be efficient with correct voltage. That can only be achieved by heavy cables. Verify what I have said at www.myswag.org
or Welcome to FRIDGE & SOLAR
Using this set up will have you to be able to run your fridge on 12 volts only when you drive. It will allow you van battery to charge as you drive. Will prevent being stranded with a flat start battery. You will arrive with a charged Van battery, charged Aux battery, a charged Start battery and a fridge full of cold beer. What more can you ask for. 3 way obsorption fridges use a lot of power and will drain batteries if not isolated when vehicle are not running.