Tuesday, Dec 18, 2018 at 14:49
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.
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
Tony
FollowupID:
895731
Follow Up By: RMD - Tuesday, Dec 18, 2018 at 17:04
Tuesday, Dec 18, 2018 at 17:04
Tony
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