wiring ?

I bought a movement actuated switch and wired it inline to the fridge. when you are driving the power is on. When you stop and there is no vibration the switch turns off the power. As soon as you start driving again the switch turns the power back on. Cost about $45 from caravan shop and a very easy wire in. Because it is wired just before the fridge it doesn't matter what you battery setup is.

It's very simple - connect the coil of a relay to an Ignition Circuit (usually at the Winscreen Wiper Motor) and Earth and then wire the feed to the Fridge via the relay contacts.

If you want it to only connect the fridge when the engine revs are high enough for the Alternator to be charging, you need a more expensive Voltage Sensing Relay exactly as used in Battery Isolators.

"i have asked a auto elecs. but they don't know or don't want to know. " - a reflection on the training of Auto electricians focussing on repairing car electrics. They are NOT trained to design electrical systems - as verified by some of their workmanship I've seen.

Have you thought of a Fridgeswitch? They have been on the market a while now. The idea is to wire the Fridgeswitch into the 12v circuit to the fridge. It cuts off the power when the van stops moving, and re-connects once the van starts to move again. I have no personal experience, but have read good reports. This should be lot easier than a custom system like the one you describe.
I am looking at an advert showing rvelectronics.com.au.
Hope this helps

I have done something like that for a friends caravan. The 3 way fridges are totally pathetic as far as efficiency is concerned especially on 12V. They suck so much current that a standard 100AH won't last long.

Originally the power to the van was wired via the trailer plug with flimsy wires. What a rubbish !! Great auto electricians around !!

I reused the two wires for another function (will explain shortly). First of all I rewired the car/van with decent 3 gauge wire (for this application 60A was ok but I always like more copper in the lines).
I have 1 gauge in my truck/camper. The car and camper was connected with an Anderson plug. Unlike 99% of all installation I do not directly connect the Anderson plug via fuse to the battery, but over a relais. There are different ways to do that. I had to run a fridge in the car with a deepcycle and the van so the aux in the car needed charge as well as the van. The Anderson plug only has power from the aux battery when ignition is on or an override switch is on. Reason: no vandal can shorten the contacts and kill the aux battery or even start battery if wired totally incompetently. One of the preexisting wires I used as a "Charge ON" wire from a voltage switch connected to the alternator (some people use a Redarc (I find they are expensive rubbish). Now along the way of the plus line I can have relais switching on to the Anderson line and connecting whichever load to the main line coming from the car.
The other wire I used to indicate that the van has 240V and the 3 bank charger in the van is on. So I can charge the car aux battery as well as the start battery from the van 20A Multibank Xantrex charger.
My friend is now on a trip around Australia since 5 months and has another 8 to go.

good luck
gmd

so what happens when you go shopping ?

You park the vehicle, the fridge WILL turn OFF ??

.... you then MUST switch the fridge back to gas ??

Or ....
do you say "I'm only going to be 3 minutes, so will not worry about it for such a short period"

you meet up with a mate and have a 'coffee' - forget the time, no power to fridge

(just too hard for me to even contemplate, I leave my fridge on 24/7)

Maîneÿ . . .

Wouldn't a dual battery relay do the same think if wired direct to the fridge?

Honky

I have wired up my 3 way fridge so that it only runs on 12v when the engine is running. I have two 75amphr batteries mounted in a box on the draw bar. These are fed from the alternator of the car via Anderson plugs and 18mms. cable with the appropriate fuses and a relay in the car and caravan. I have utilised the 7 pin (large round) to feed a second relay in the caravan in the caravan to isolate the fridge from the two batteries when the ignition is turned off. When the ignition is on the fridge draws it's power from the two batteries on the draw bar which is being powered off the car alternator. Don't ask for a diagram as I am a lousy drafts person.