12S wiring, IS A 4 PIN RELAY OK?

[Gareth111278]

Hi.

I'm going to wire our second car up with a 12S socket just for one weekend. I'm lothe to shell out on a Smartcom or similar relay for such a short time.

Can i just use a 4 pin relay [like you'd use for driving lights for example] and connect the fridge and caravan battery feeds together off it?

Any thoughts would be greatfully received

Gareth

 

[rayc]

Gareth, you can use any 12v relay that is rated across it contacts for 10amps or so. You could connect its operating coil to point that is ignition fed e.g a 12v socket in the rear laod area of an estate car { make sure it is only live when ignition is ON). Get a relay that will the fridge supply and battery charging/permanent feed supply independently if you can.

The question that comes into my head is this all really important for one weekend? Do you really neeed to charge the van battery or keep the fridge going en route. Why not get the fridge cold and put a bottle of frozen milk or water inside and charge the battery up before leaving home?

 

[rob_jax]

Hi Gareth,

The fridge and caravan battery charge are two completely different circuits - which could be fed from one 20 amp supply.

The fridge feed normally has the SmartCom voltage sensing relay that only supplies power to the fridge when the engine is running above idle speed - and the alternator is producing enough current to supply the extra load.

Inside the caravan, that same fridge feed is also connected to a (habitation) relay - and this diverts electrical power from the permanent live feed to charge the battery.

So what would you achieve by using a "dumb" relay?

1. It could be wired to provide 12 volt power to pins 4 and 6 in the 12S connector - feeding power to the fridge (6) and caravan battery (4)

2. It could be activated by the cars switched 12 volt supply.

3. This will provide power to the fridge and the caravan battery as soon as you put the key in the ignition. That may not be ideal - it'd be like starting your car with all the headlights on.

4. And you'll need a 20Amp fuse in the heavy duty wiring between the battery and the relay.

If you want to replicate the "voltage sensing" relay but using you as the smart bit - then a manual 12 volt switch in-line with the supply that energises the relay would work:

You put the key in the ignition, 12 volts flows from the switched supply - but is interrupted by the switch - you start the car - flip the switch - the energising power now flows to the relay and switches on the heavy duty supply to the fridge. But you need to remember to open the switch before starting the engine.

Robert

 

[WatsonJohnG]

That is very intersting Rob and I have never loked at it like that(load etc)

I always use 2 4 pin relays with 2 feeds off the car battery because if you use 1 fuse and lead and it blows then without you knowing the van battery will be discharged by the fridge on tow

I follow the logic of the Smartcom and the load etc but have had trouble with them and so have friends whereas I have yet to have any problem starting using the 4 pin relay in over a decade.

If the relay is triggered by say the socket in the boot doesn't the car circuitry cut all else out on starting and so the load would not be on until actually started

I am not being confrontational just interested in your views

Regards

 

[rob_jax]

Hi John,

"doesn't the car circuitry cut all else out on starting and so the load would not be on until actually started"

It might do, but it probably doesn't - and it'll be car dependent and how you wire the "thing" into the car. A 12 V bulb or a multi-meter is the easiest way to find out how your car works.

I agree that using a separate relay to switch each circuit is much the best idea.

Robert

 

[Gareth111278]

Hi guys i was thinking about this whilst driving yesterday, 2 relays will be needed as when the engine is off the fridge will run off the caravan battery as they are connected together at the relay.

As for is it worth the hassel i have all the bits kicking about in the shed, the pain in the neck will be running a 20A and a switch wire front to back of the car!

Does anyone have any views either way on going through the car cabin or under the body?

 

[rob_jax]

Gareth,

If it's only going to be installed for two or three days - then it makes no real sense rooting about inside the car to run a dedicated 20+ Amp feed wire through the interior.

Also many cars now use moulded bulk-head connectors - rather than grommets - so you may have fun trying to run an extra wire inside...

Robert

 

[Gareth111278]

Hi rob

Its a 1995 Cavalier! so not the newest thing on the road!

i'm thinking i might run a 20 A under the car from the battery fused at the front , then tag off the side light to switch it! i run on sides most of the time when towing anyway. this way i retain control over when i put power to the relay. i.e. after starting the engine.

It'll do for one weekend and be easy to plug into the car if we use the TV too much!

Cheers Gareth

 

[WatsonJohnG]

Fun inded Rob

I spent over an hour trying to find a way through on the new Nissan XT and failed

I ran caravan black waste piping(and a lot of nylon ties) under the car as trunking and threaded the wires through that

 

[Gareth111278]

That sounds like the way to do it !

i'll have a go once the weather warms up a bit. [looking forward to this storm!!]

Gareth