Dual Battery Setup - Can I connect fridge and aux battery to Isolator?

Derek, you are saying that the system that most people with caravans have will not work !!

Ian

Hi Ian
Obviously does not work ,as shown by number of posts perpetuating the MYTH that 3ways are no good on 12v
Derek's posts is correct, run separate heavy cables for fridge back to tug battery with an ignition controlled relay in circuit to disconnect fridge when engine is turned "Off'
Running of van battery en creases problem of van battery receiving max possible charge ,due to voltage drop in long undersized cables

Mine seems to work OK, but then I have 25mm2 cable x 2 from car batt to caravan. Not a lot of voltage drop there !!

Ian

Ozhumvee replied:
"The 12v section of a threeway frig is purely to maintain (which most can't they slowly defrost) frig temps while mobile.
Peter "

Hi
So that Myth cotinues to be perpetuated.

A 3way fridge usually has the same size [watts]element for both 12v & 240 v
Same heat input, works the same on both!!

The major problem with 12v operation is that THE FRIDGE IS NOT GETTING 12V @ it's terminals DUE TO UNDERSIZED WIRING
The other problem is that few are correctly installed [ventilation ,draught to cool etc}
Many , many threads on the sublject.

If both ares done correctly then they will not only maintain freeze but can actually cool down further if thermo is changed to lower temp
But do not use them without engine running or having ignition controlled relay fitted,will flatten bat very quick

Yes that is true about the wiring and most caravans and campers have inadequate wiring from assembly to run the frig on 12v effectively.
The only time I ever got the ones I had (bin type and van frig) was to connect them to the battery direct with jumper leads, even then if the ambient was over 25 deg C (which it probably would be in a closed van or camper with a frig heating the air) the 3 ways struggle.
It is much easier to get 240v to the frig than a "proper" 12v supply hence the fact that they usually work much better on 240 than 12v despite the elements being the same size.
The later model van frigs with better design and insulation do work ok on 12v even in the tropics but you had better have plenty of 12v supply to keep them going.

Our fridge in the van has a 125w 12v element, but has a 175w 240volt element. 12v works fine up to about 30c. Will even freeze ! (with fans).

Ian

Thanks guys, I think I'll go with the direct battery connection and ignition relay as recommended by most.

Cheers
Mickos

Mickos1,
remember when using an "ignition activated relay", only when the car is running will the fridge be running, a simple on/off inline switch will give you more control over the fridge run time, but yes, you will still have to remember to turn the fridge onto gas, and off 12v at the same time.

Maîneÿ . . .