Caravan Power Isolator Switch

Submitted: Tuesday, Jun 27, 2023 at 21:09
ThreadID: 145923 Views:3643 Replies:3 FollowUps:1
This Thread has been Archived
I'm confused about the functionality of the isolator switch fitted to my van (2008 Newlands Concept).

It has two positions: CAR and POWER (it looks to be a household wall switch)


I assume it should function thus:

1. In POWER, everything in the van can receive 12VDC from the house battery EXCEPT for the fridge 'motor'. The fridge light and the gas igniter still get 12VDC, as do all lights, pumps and sockets in the van.
This prevents the fridge drawing high-current power from the house battery when you are parked if you forget to switch over to gas or 240V.
I've checked the operation, and it all works as expected.

2. In CAR, everything should be isolated from 12V, EXCEPT the fridge which will now only operate on 12VDC. This prevents water pumps/lights etc operating while you are underway, and the high current-draw fridge 'motor' is now fed by the vehicle alternator (not the house battery).

On my vehicle I have the power wire at the trailer plug connected to my vehicle auxiliary battery, so power is available to that circuit on the van at all times the trailer plug is connected, not just when the alternator is operating. I also have a separate anderson connection which feeds the van house battery directly.

My problem, is that in CAR, everything isolates as expected, until I plug the van to the vehicle, then I get 12V to everything in the van, including to the fridge 'motor'. So I'm losing the isolation feature. I get the same issue with the anderson connected or disconnected (I thought it may be feeding stray current somehow).

I assume there must be a large relay somewhere in the system that connects the house battery to the van with POWER selected, but I can't find it anywhere. Might it be located behind the fridge? I can hear clicking but think this might actually be the fridge switching over.

Any ideas? Anyone have knowledge of this type of circuit, or a basic diagram? I have some limited electrical knowledge but my probing with a meter has yielded little results. With most of the wiring sandwiched inside the van walls it's hard to trace the wires.

Or, is the switch really just a fridge changeover switch and not really an isolation switch?
Back Expand Un-Read 0 Moderator

Reply By: Member - McLaren3030 - Wednesday, Jun 28, 2023 at 06:48

Wednesday, Jun 28, 2023 at 06:48
Hi Beatle Bayly,

Whilst I am not an Auto. Elec. or a 12 volt expert, I don’t think you are correct with your assumption.

From the older van I had that was set up with one of these switches, when switched to “Power”, the van was being powered by the 240 volt connection to a 240 volt mains power source. When switched to “Car”, the van is receiving 12 volt power from the towing vehicle. If you are not connected to a 240 volt mains power source, switching it to “Power” would basically result in nothing working in the van. If the absorption fridge has an “auto power source” sensor, it would most likely switch to 12 volt from the house batteries if you have them. Some older vans did not have house batteries.

As an aside, an absorption fridge does not have a “motor”, it has three heating elements, one 12 volt, one 240 volt, and an LPG burner. Unless it has had a circulation fan added to it, it does not have any moving parts.

Macca.
Macca.

Lifetime Member
My Profile  My Position  Send Message

AnswerID: 643997

Reply By: Andrew L - Wednesday, Jun 28, 2023 at 11:07

Wednesday, Jun 28, 2023 at 11:07
Id assume you set this switch to select if you want to run from 240 or 12v
AnswerID: 644000

Reply By: Beatle Bayly - Tuesday, Jul 18, 2023 at 21:09

Tuesday, Jul 18, 2023 at 21:09
OK, so after a few hours head scratching and probing with the multimeter I can confirm that the switch does not isolate all 12V supply into the van. It switches the 12V input from either the house battery, or the 'alternator' supply wire, and all it does is switch the fridge supply from 12V-only, to 240V/Gas-only. The van 12V fuse block receives 12V in both switch positions.

It would be possible to do some rewiring to make it a proper isolation switch, but that would require chasing wires through the insulated wall panels........
AnswerID: 644136

Follow Up By: Nomadic Navara - Wednesday, Jul 19, 2023 at 18:54

Wednesday, Jul 19, 2023 at 18:54
I missed this when you first posted it, so here comes a little history for you. From what you have said it is clear that the electrics in your caravan are far from original.

The vans from the 2000s and earlier that had a switch like that did not come with batteries. Vans were not commonly supplied equipped with 12 V batteries until the 2010s. They generally did not come with 12 V power points or car radios built into them. Vans built in the 1970s through to the 1990s nearly all had two electric circuits for their lights, the light fittings had both 240 V and 12 V globes in them. The 12 V lights were supplied directly from the tugs battery (along with the fridge when they went from 2 way to 3 way models.) In those days our 12 V lighting was easily supplied from the car battery when you plugged the trailer plug into the tug.

In the 1990s manufacturers started putting 12 V lights into vans and no 240 V lamps. The lights were supplied from a transformer (ie 12V AC) or sometimes an 12 V DC power supply. Those vans had a switch like the one in your van so the 12 V supply from the mains power would not feed back to the tug battery or the fridge. I reckon your van would have been delivered without a battery or battery charger. One of the subsequent owners would have added those. We would not be able to guess how things would have been done when the 12 V power supply was upgraded. It's just as well you have some idea of how to chase thing out.

When I purchased a new van in 1997, I sat down with the licensed electrician working in the factory and explained what was required in 12 V systems in vans. Back in those days very few electricians had any idea of caravan 12 V power systems. When I mentioned that I would like to convert the exterior light to use a high efficiency fluoro light he mentioned that Hybralec had some new exterior lights with 2D tubes in them to trial. He rang them and as a result I had one of the first of those fitted to my van. Up until then, all 12 V lighting in vans was car type globes of QI globes. Things progressed slowly from then until the mid 2010s when nearly all the vans came fitted with a 12 V battery or provision to fit one.

When you rewire your van you may consider scrapping that switch. My later two vans have not had them fitted. If you do install an isolation switch, I suggest you just use a high current breaker and position it so you can remove all phantom currents from your battery. Just have your solar system connected to your battery when you isolate it.
PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

1
FollowupID: 924147

Sponsored Links