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Old 03-26-2008, 02:22 PM   #1
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Default Add a relay for fridge to prevent dead battery

I need to add a relay system to my 94 RT to ensure that the fridge will only run on 12V when the engine is running. Objective: avoid the possibility of a dead battery. This needs to be thought through as to overall logic

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Old 03-26-2008, 04:45 PM   #2
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A simple fog light relay from any auto parts store would do the job but you have to find a source to enable it. The ignition would be a good one but I don't know how difficult it would be to run the wiring for it.

You also might want to concider placing a switch on the system so you can run the fridge when the ignition is off.
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Old 03-26-2008, 05:51 PM   #3
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If you are trying to avoid having a dead engine battery from running the fridge on 12v then I think Roadtrek already built that in with the isolator in your '94. My '04 had it.

The fridge should be connected to the house battery. When the engine is running, the house battery and the engine battery are combined so that both get charged. When the engine is not running, the engine battery is "isolated" from the house battery by the isolator. The fridge could run the house battery down but not the engine battery.


If you are trying to avoid having a dead house battery from running the fridge on 12v that's more involved. In my RT, I just had to remember to either switch the fridge to electric, off or propane, depending on what was best at the time to avoid running the house battery down.


Dave posted great info about Battery Cutoff Devices (retail and home-made) on his site here: Cutoff Device

Here's the link to the rest of Dave's site:
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Old 04-06-2008, 07:50 PM   #4
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Yes, the point is that running down the house battery, being a very poor idea, is to be avoided. The only time I can see running the refer on 12 V is while going down the road, when lots of amps are available.

Being careful not to leave it on 12V is to be avoided, with a brain like mine. My modern refer in my 33' Holiday rambler, figures out the proper priorities all by itself, but even it could kill the battery if you let it.

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Old 05-11-2008, 02:40 AM   #5
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Default Add a relay

I have had such a relay in my last 2 rigs, it is very simple.
Buy a 12V relay at an Auto parts store or Radio Shack and mount it in the back of the fridge. Cut the wire running to the 12V fridge heater and attach the ends to the normally open contacts. attach one of the relay contacts to ground and run a wire to the engine compartment from the other contact. Fuse this wire and attach it to power that is only on when the ignition is on. When the fridge is on 12V you can shut off the engine and the fridge will still think it is on but there will be no power to the heater. start up after lunch or shopping and it is back on.
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