Different 12v power set up for travel

1246
For a 3 way fridge to even attempt to work there should be nothing between it and the power source.
The breaker you have on the main battery is immediately after the battery post, good idea. However the breaker on the aux battery isn't first item after the battery terminal, perhaps it should be. Do you have an isolating solenoid to stop fridge flattening vehicle battery?
I cannot see any advantage running fridge power through the solar controller as that only means some additional resistance to current flow from whatever power source you have and so lessens the fridge performance, which is poor on 12v anyway. Is the solar controller actually able to handle a 20 amps or more initial load, 15 amps running but more when the element is cold at startup. If it a MOSFET controller/switched unit they may pop under heavy load. Best to know that rating.
The fridge will draw around 15 amps and so ANY wiring in the circuit from battery to fridge heating element needs to be quite thick, bigger size than most caravans ever fit for their fridges. That will ensure the maximum of voltage/energy to the heat element from the battery.
What size is the battery in the van? Two hours of 15amps will reduce a 100AH AGM to fairly low voltage which must then be replaced when driving. Therefore, the engine alt supply has to be able to supply the 15 amps of continued fridge use + the current flow to recharge the battery. That requires heavy cables from engine battery solenoid, to Anderson plug and also in the caravan right up to the battery and also the return line so it can all happen and a good charging voltage realized at the van battery terminals all while under load in the driving time left that day.
If there is any deficiency in cable sizes the van battery will never be/get to near full charge and so will have far less than full AH capacity each time you begin a two hour jaunt with the van battery supplying the fridge for maintenance coldness.
You may think you are starting with 100 ah usable, in reality that is around 50 AH if battery life is also considered. If it was never near fully charged, then that 15 amp discharge which is far more than the way the battery is rated for 100AH will see the battery progressively go flat with multiple stops.
Total of charge time, either running or when parked for the night, has to be considered to allow the battery to recover.
While travelling after a stop.
After a stop there will be continued 15 amp draw, plus two hours of 15amp = 30 ah at least. so the alternator has to be able to get full flow to the battery to overcome 45amp flow or more for quite a while. Good cable size, decent terminals and connection integrity will be essential to prevent problems developing.

PS, If using the fridge on gas or when stopped and running on 12v, a couple of computer fans delivering cool air to, and exiting air from, the hot bits of the frige will increase it's performance while running on any power/heat source.

Really one of those how-long-is-a-piece-of-string questions without the numbers.
It is a workable solution, subject to:
> the capacity and condition of the van battery
> the ACTUAL DC current draw of the fridge
> the rating and actual output of the solar panel & reg
> the sun shining ...
If the panel/reg output under "normal" insolation is somewhere near the fridge draw, and the battery is half-decent it should suffice.

Edit: RMD's more comprehensive response came in while I was typing.

Dust proofing the Jayco should be a high priority as well.
If you don't you'll be very sorry.
Cheers

I would have thought the simple answer would be
If your solar can put out enough to run your fridge while you are stopped everything will be hunky dory.
If it doesn't put out enough to run the fridge at some stage it will all go pear shaped.
So probably 250 or 300 watts of panels?

Travelled up north yrs ago it in a pop top last thing I wanted to do was deliberately park in the sun if shade was available I had one battery in the van would leave it on power for 30minutes or so other than that it doesn't take long to flick over to gas.
If your looking at a couple of hrs which may or can turn into a few or more so you don't have to rush around and miss things just because of a fridge then a much larger battery supply would be better just in case. It could be cloudy as well myself I would go 300ah plus with plenty of solar panels not just one 250w but weighing up all the cost it's easier to turn on the gas for piece of mind. Or if it's a van your keeping for the long term spend the extra and get a 12v fridge batteries and solar to suit so when you turn the car off you can just walk away and let the system look after itself.

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Hi 1246,

As well as agreeing with what has already been said, you MUST have an automatic isolator between your car battery/alternator and the van battery. Otherwise it is almost certain that you will return from a hike to find that you have two flat batteries and no way to start the car.
It is a simple install and only a few dollars to add an isolator into the circuit.

Thanks again guys...input has been most helpful, and much appreciated.