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12 S wiring

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Posted

My sister wants me to install an 12S socket and wiring on her vehicle.

She hasn't got a fridge - only battery - that's all she wants wired up. Am I correct in thinking that I need Green for 12v positive and white for the earth?

Also - is there the need to fit a relay on this feed from the battery so that charge of the battery only occurs when ignition switched on or is that personal preference?

Many thanks.

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6 answers to this question

Posted

Much would depend on how the caravan has been wired, which would depend on it's age 1999 was change over year - Have a look here

If the caravan was built and wired after 1999 then you will need to wire for the fridge as this triggers the habitation relay in the caravan.

And yes I would fit a relay in fact I used one of these:

split charge.jpg

Fused live and neutral in ~ live and fridge out - no sweat

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Posted

You can fit a smart (voltage sensing) relay, or you can operate a dumb (ordinary) relay, switching it from the accessories circuit. The former is the easiest and is the most common way of doing it these days, but the latter has its advantages, especially as the voltage sensing relays can be fooled in certain situations (I've had one that would happily connect the caravan battery while cranking the engine if you'd just stalled it.)

If you're lucky, the car will already have a suitable feed through to the boot area, though you'll need a multimeter to find it, seeing which pin goes live when you fit the appropriate fuse in the cabin fuse box. If you're not, then you'll need to run a feed from the battery. This usually involves either finding a way through the bulkhead or running conduit along the underside of the car.

Use decent gauge cable (I recommend a minimum of 27A rating to reduce voltage drop) and if you're running from the battery, fit a fuse holder and 15A fuse as close as possible to the positive terminal.

From memory (I'd check this first, because I could be wrong) a universal configuration has pins 2,5 and 6 ignition live, pin 4 permanent live and pins 3 and 7 grounded (each with its own wire direct to the car body.) Optionally, pin 1 can be connected to the car's reversing lights to operate reversing lights on the caravan (if it has them.)

Older caravans use pin 2 to charge the leisure battery, pin 4 to power the caravan when pitched and switched to 'car' mode, and pin 6 to run the fridge when towing. Pins 5 and 7 are unused. Later ones used pin 4 both for 'car' mode and battery charge, switching the latter with a relay operated by pin 6. Pins 5 and 7 became used at a later date to beef up the power and ground return for the fridge circuit, as more powerful modern fridges tend to overload (and melt) the standard pins.

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Posted

As can be seen in the circuit diagram from the link above, the battery charge circuit is fed directly from the alternator (via a 25 amp fuse). I personally wouldn't fit a relay, just something else to go wrong.

In this scenario, (no fridge installed) as soon as the engine is running and the alternator turning, both batteries will be charged.

As long as the caravan is not left connected to the car with loads of accessories/lights on, all will be fine.

As Del Boy would say, " plume de ma t'aunt".......ebt

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Posted

As can be seen in the circuit diagram from the link above, the battery charge circuit is fed directly from the alternator (via a 25 amp fuse). I personally wouldn't fit a relay, just something else to go wrong.

In this scenario, (no fridge installed) as soon as the engine is running and the alternator turning, both batteries will be charged.

As long as the caravan is not left connected to the car with loads of accessories/lights on, all will be fine.

As Del Boy would say, " plume de ma t'aunt".......ebt

actually it's not, the alternator circuit triggers a relay

The circuit shown is for a post 1999 caravan with it's own habitation relay - the habitation relay switches the permanent 12 volt feed between supplying a feed for the caravan 12 volts (lights, pump, etc) when the tow vehicle engine is not running and charging the caravan battery when the engine is running.

If you are wiring for a pre 1999 caravan then using the smart relay I pictured and take a feed from the 6 terminal (I think) to pin 4 of the 12s socket

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Posted

actually it's not, the alternator circuit triggers a relay

The circuit shown is for a post 1999 caravan with it's own habitation relay - the habitation relay switches the permanent 12 volt feed between supplying a feed for the caravan 12 volts (lights, pump, etc) when the tow vehicle engine is not running and charging the caravan battery when the engine is running.

If you are wiring for a pre 1999 caravan then using the smart relay I pictured and take a feed from the 6 terminal (I think) to pin 4 of the 12s socket

:goodpostingsign:

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Posted

Thanks everyone for the advice.

Her 'van is old - so old that the entire body is steel. I took the socket apart on the van and not only did it start to crumble in my hand but some of the wires are so old that they've lost the colour!

I've run a decent cable from the battery end of the car and put in a 30amp fuse in - and I went for the 'dumb' relay for the reasons Dave points out (and because I have a pack on them in the garage!). I take EBT's point about something going wrong but I don't want her to run anything in the 'van whilst hooked up to the car and with the engine off which might end up leaving her stranded.

I haven't yet decided what to do past the point of the hook up in the van to charge the battery but I am going to run brand new cable from the plug to the battery. Is there a device is best suited to splice into the cable for the battery terminals given that I'm going to bypass the original electrics? I guess I'll be find to hook straight in to the existing terminals - anyone got an objection to that - should I still use the smart terminal?

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