3 Way Fridge Wiring
Submitted: Monday, May 20, 2019 at 06:34
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Daniel G3
Hi
I have a 2017 Kokoda Major Extreme van which has a Thetford 164 litre 3 way fridge.
There is an anderson plug at the draw-bar which has 2 actives and 2 negatives crimped together at the plug.
I have been able to trace one of these wires which goes through a 30 amp fuse and connects directly to my 2 x 100 amp/hr batteries.
The other wire is difficult to trace but I think it goes directly to the high current side of the fridge. There is a second wire which operates the display panel on the fridge connected to Low current connection at the back of the fridge.
With anderson plug not connected to my vehicle the fridge will not run ( I have tonged for current at the fridge). I connect the anderson plug to my vehicle which is running and get 15 amps at the fridge and 1 amp from the second wire which runs to my batteries. Disconnect it and fridge stops. How is this possible? I do have some electrical knowledge and cannot understand how this is possible. I want to make sure that my fridge cannot run from my van batteries.
Is there some smarts in the fridge that makes this happen? As far as I know it is not an auto sensing fridge which looks for the best power source.
Reply By: Allan B (Sunshine Coast) - Monday, May 20, 2019 at 10:23
Monday, May 20, 2019 at 10:23
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Hi Daniel,
As Swampy has said, it is probable that a diode is fitted in the battery feed to prevent output to the fridge. (Block Diagram 1, below) The diode is quite small and may not appear obvious to you.
However, a diode (even Schottky type) will introduce some small voltage loss in your charge voltage and you are already suffering loss in the wiring volt-drop.
An improved scheme is as per Block Diagram 2 where the diode is replaced with a DC-DC charger. This will also prevent feed to the fridge but will overcome volt-drops and provide multi-stage battery charging. Some models of charger have provision for solar input to the batteries without the need for a solar controller.
Block Diagram 1
Block Diagram 2
AnswerID:
625627
Reply By: RMD - Monday, May 20, 2019 at 12:21
Monday, May 20, 2019 at 12:21
If there is no voltage drop in the line to the van batteries from the Anderson plug point, checkable with volt Meyer when not connetced, then the van may have a vsr type device fitted somewhere and it switches the fridge to ON when sufficient voltage is applied.
Also, if running two big van batteries which may be discharged a bit AND 15amp fridge load as
well, besides good sized cabling, I would double the size of the POOR alt to main battery cable. These are small as OE cables and ok for normal use, BUT when charging constant high loads which does happen for lengthy periods, that poor cable acts as a restriction resistance because it runs very bloody hot and IS part of the charge circuit. It runs hot purely because of engine heat alone and not only from amp flow.
I doubled
mine in an earlier vehicle to attain alt voltage to run headlight relays for lights. 55w globes drew less Amps, ran high colour temps and gave more light than 100w globes did before the mod and 1/2 the Amps required. There were other advantages too.
AnswerID:
625629
Reply By: Member - Jim - Friday, May 24, 2019 at 16:41
Friday, May 24, 2019 at 16:41
Daniel,
I have a Kokoda Salute and when delivered the wiring was:
Anderson Plug to Van Batteries and Van Batteries to the Fridge high current.
The 12v Fridge control was fed from the van batteries and when the van power was isolated at the switch so was the fridge control.
I located the wiring from the Anderson plug at the batteries and connected it through to the fridge high current (bypassing the batteries) and changed the control circuit to it's own switch so that it was not isolated when turned off.
I have no need to charge the batteries from the car, leaving that to the solar panels when towing. If I ever need to do this I will install another feed from the car and a DC-DC charger for this.
It works
well, and the batteries will thank you for taking the fridge off them.
Cheers,
Jim
AnswerID:
625724