Different 12v power set up for travel

Submitted: Tuesday, Dec 18, 2018 at 14:04
ThreadID: 137571 Views:3525 Replies:7 FollowUps:7
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Hi all
I have wondered about a particular set up i would like to use and hoped for some input from you experienced folk on that setup
I am travelling in a poptop (Jayco Hawk)thru western Qld next year and at times be stopping for a couple of hours here and there.
Whilst stopping in the heat of the outback i am concerned for the increased temp inside the van and the 3way fridge. I would like to have the fridge run on 12v for a couple of hours while exploring etc, without the need to crawl inside and switch the fridge over to gas for short periods to keep things cool.
I will remove my ‘fridge switch’ and was thinking of the setup to resemble that found in the attached picture where the power for the fridge runs from the batrery in the van via solar controller load with a solar panel on the roof.
This is only for the short stops being made to keep the fridge cold.
Thoughts on the idea or things i should do?
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Reply By: RMD - Tuesday, Dec 18, 2018 at 14:49

Tuesday, Dec 18, 2018 at 14:49
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.
AnswerID: 622696

Follow Up By: 1246 - Tuesday, Dec 18, 2018 at 16:11

Tuesday, Dec 18, 2018 at 16:11
Thanks RMD
I will now be looking to increase the cable size.
My drawing may not be clear but it indicates the anderson plug to breaker to battery on van and the solar charge controller(20a) goes to battery also.
I already fitted a thermo fan in the vent cavity for the fridge to assist.
The only thought about the solar controller is that i can set the off voltage to say 11v and perhaps still have enough to kick the car over....
No i dont have a isolating solenoid on the car battery. Was hoping not to have to have a dual battery setup given i will only ever have one battery in the car. Can you get isolators on their own so to speak?
I need to replace the battery before i go so will ensure it is decent capacity or two of. Thx again
FollowupID: 895731

Follow Up By: RMD - Tuesday, Dec 18, 2018 at 17:04

Tuesday, Dec 18, 2018 at 17:04
It is pretty simple to fit a constant duty solenoid which only connectes the vehicle to the van while engine is running, That way you are leaving the vehicle battery out of the equation.
Having a battery in the van charged by the engine alt and battery in the vehicle, means you have a dual battery setup. Maybe not as fancy but dual all the same.
If relying on solar, ie, full sun, for the power regulated power to the fridge, you would require about 300 watts to 350watts of solar panel to provide the energy to run the fridge, minimum. Solar panels aren't always at the optimum angle for energy conversion and so way more than solar is required because the sun angle isn't optimal. At lunchtime in summer, maybe ok, morning and afternoon far less output. In winter, unless you can aim the van roof at the low angle of sun, the output will be easily reduced to half in many cases. Anyone for 500 watts of solar?
Unfortunately all these whizz bang systems have limitations which have to be overcome by thoughful design.
FollowupID: 895736

Reply By: Zippo - Tuesday, Dec 18, 2018 at 14:50

Tuesday, Dec 18, 2018 at 14:50
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.
AnswerID: 622697

Reply By: Crusier 91 - Tuesday, Dec 18, 2018 at 14:55

Tuesday, Dec 18, 2018 at 14:55
Dust proofing the Jayco should be a high priority as well.
If you don't you'll be very sorry.
AnswerID: 622698

Follow Up By: 1246 - Tuesday, Dec 18, 2018 at 16:12

Tuesday, Dec 18, 2018 at 16:12
Thx for the tip mate
Any thoughts as to best method?? Duct tape?
FollowupID: 895732

Follow Up By: Crusier 91 - Tuesday, Dec 18, 2018 at 17:15

Tuesday, Dec 18, 2018 at 17:15
I had a thread on the myswag forum showing what I did with my Jayco Finch.
Sealed the door vents and fridge vents with leather look a like material that velcroed on.
Extra rubber all round where roof meets base when wound down
Sealed all joins (where floor meets wall) especially around internal wheel arches, under seating and drain hose under sink, around fridge, etc.
Did what this guy did on his Jayco
Check the rest of his vids.
portable filter in roof hatch
You'll need aero matting under mattresses so they don't go moldy
I also used yoga matting around the bed bases to keep the bedding off the canvas when wet.
FollowupID: 895738

Reply By: terryt - Tuesday, Dec 18, 2018 at 15:52

Tuesday, Dec 18, 2018 at 15:52
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?
AnswerID: 622700

Follow Up By: 1246 - Tuesday, Dec 18, 2018 at 16:21

Tuesday, Dec 18, 2018 at 16:21
Yeah will have 250w....
FollowupID: 895733

Follow Up By: RMD - Tuesday, Dec 18, 2018 at 17:18

Tuesday, Dec 18, 2018 at 17:18
250 watts of solar will only nearly work if used at lunch time/midday in the summer.
My 240watt panels, directly aimed at the sun in December produces only a max of 12 amps or so depending on temp of panels. Good hot day = less than sunny cool day where panels are colder/not as hot. Theoretically more, but actually far less than the figures/specs indicate. In winter reduce that. If near trees, less again. Any slight shading will dramatically drop the output. Just one small slightly leafy branch will render the whole system very low output while you are away.

Any dust or dirt on panels reduces the energy harvest even more and is a common thing which causes inefficiency of the energy conversion. Keep 'em clean.
FollowupID: 895739

Reply By: Batt's - Tuesday, Dec 18, 2018 at 17:31

Tuesday, Dec 18, 2018 at 17:31
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.
AnswerID: 622703

Reply By: Allan B (Sunshine Coast) - Tuesday, Dec 18, 2018 at 18:20

Tuesday, Dec 18, 2018 at 18:20
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.

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AnswerID: 622705

Reply By: 1246 - Tuesday, Dec 18, 2018 at 23:17

Tuesday, Dec 18, 2018 at 23:17
Thanks again guys...input has been most helpful, and much appreciated.
AnswerID: 622710

Follow Up By: 1246 - Friday, Dec 28, 2018 at 18:54

Friday, Dec 28, 2018 at 18:54
I ended up adding in a dual batt system and upgraded cables to the fridge. Thx again.T
FollowupID: 895887

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