This topic comes up from time to time.
If you are running the fridge on 12 volts while towing and then stop for dinner you may drain the batteries.
Some of us have solved the problem by adding a battery disconnect switch and unplugging the TM from the TV.
This has a problem because you have to remember to switch the batteries back on and plug the TM back into the TV.
I have found a product that seams to be an automatic solution to this problem.
Automatically disable your refrigerator when there is no 12V charging source.
This is a simple way to make sure you don't discharge or even destroy your house battery by forgetting to turn off your refrigerator load. Many installations only have the capacity to support the refrigeration while on shore power or when the engine is running. But a manual switch is often forgotten when you start the engine, wasting refrigeration time, or even worse, you forget to turn it off and deplete your battery after the engine is turned off.
The process can be automated by installing a Combiner 50 between the refrigerator and the battery. One red lead goes to each, and the black ground lead is connected to the 12 volts negative. Whenever a charging source raises the battery voltage above about 13.3 volts, the combiner will close and supply the refrigerator. When the voltage drops, it will disconnect. The built in timing circuits in the C50 will prevent short cycling that is detrimental to refrigeration motors. No power is used by the C50 when the refrigerator is not running.
If you want to be able to manual override the automatic control and allow the refrigerator to run while no charging source is available, you can add a small switch to the remote control feature of the Combiner 50.
I found this at:
http://www.yandina.com/hints.htm#Frig
I have no connection with the web site or the product that it refers to.
Preventing battery drain from fridge on 12volts
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