12v supply to trailer via caravan socket - Hugo {P}
My Ifor Williams electric tipper works off a 12 volt battery contained within the trailer that needs to be charged up periodically.

Never having had a caravan or even bothered with the 2nd socket on any car could someone please tell me what I would need to do to be able to charge this from the Land Rover.

There is a caravan socket on the tow hitch for this vehicle. I believe all the wiring is there as previous owners used to tow a caravan with it.

Would there normally be a charging relay in the car to prevent the car battery going flat should the trailer battery develop a fault? And if so then I guess I would simply need some heavy gauge cable (live and neutral) going from the 2nd plug to the battery - Am I right.

Thanks in advance
12v supply to trailer via caravan socket - henry k
I know nothing about the subject but to stop you getting bored waiting for an expert reply.
Caravan electrics into Google produced over 1M hits and trailer electric 0.8M hits so no wonder you are after a short cut response.

www.rydertowing.co.uk/pages/checklists_intro.htm
has a link to a 50+ pages practical guide

www.caravanninglinks.co.uk/electrics_wiring_code.h...m

www.towbarsdirect.co.uk/products.htm gives some info re split charge relays
12v supply to trailer via caravan socket - jc2
A lot depends on the age of the wiring;before rear fog lights,sometimes one of the pins in the 12N socket was used as a power feed(I used it for tent lights and fridge) but later systems used a seperate extra pin or a 12S socket.Sounds as if you would need a relay or at least a diode to stop back feed.Have a word with an auto electrician.
12v supply to trailer via caravan socket - RichardW
From what I remember 12S socket used to wired with 3 'lives' and an earth. 1 of the lives was permanent, which allowed lighting etc to be used in the 'van off the car battery. The other 2 lives were switched by a relay when the engine was started (powered up off the alternator output) and were for battery charging and running the fridge. No protection against faults in the van other than normal fuses.

So you just need to make up a cable with a 12S plug on one end (actually they're identical except for the colour) and just wire in a two core cable to one of the live pins and the earth pin, and fit croc clips on the other, then connect up the battery when you go for a run. For a more permanent installtion you could fit a change over switch to go from power to charging.

Link to 12S wiring scheme - homepage.ntlworld.com/mark1968/Towing%20&%20Wiring...o Looks slightly different to when I was doing it, however, you should find pin 4 goes live with the engine running.
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RichardW

Is it illogical? It must be Citroen....
12v supply to trailer via caravan socket - Ruperts Trooper
12N (black) and 12S (grey or white) AREN'T identical apart from the colour! The pins / tubes are different to prevent incorrect connection.

To simply charge a battery on the trailer:-
Pin 2 of the 12S circuit should be connected to a) car battery via an ignition controlled relay and b) to trailer battery.
Pin 3 of the 12S circuit should be connected to earth on car and trailer.

Use 30A cable to minimise voltage drop and include 10A fuses between car battery and relay and between trailer battery and plug.

Before rear foglights were compulsory (late '70s?) pin 2 of the 12N plug/socket was used to provide 12v power to the caravan when parked.
12v supply to trailer via caravan socket - RichardW
"12N (black) and 12S (grey or white) AREN'T identical apart from the colour! The pins / tubes are different to prevent incorrect connection."

I stand corrected - makes sense. The url I posted does show that 7 is a pin a 12N plug and a socket in a 12S plug. Tis about 12 years since I played with trailer electrics though.... then I could wire both from memory, and knew what all the 12N wires were for.


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RichardW

Is it illogical? It must be Citroen....
12v supply to trailer via caravan socket - Cliff Pope
If the two batteries are always at approximately the same state of charge then I don't think there should be any problems from simply linking them.
But what happens if the trailer battery were run right down, for example? Wouldn't the alternator try to charge it at maybe 100 amps and burn the cable?
Or alternatively you might risk flattening the main battery by over-use of the trailer motor.

I'd be tempted just to dispense with the trailer battery and connect some long leads with crocodile clips to the main battery when required.
12v supply to trailer via caravan socket - Ruperts Trooper
Caravanners live with these theoretical problems all the time but they never materialise!

The circuit I suggested would be fused at 10A, much less than the cable rating of 30A.

The main battery won't get flattened as the two batteries are only connected when the engine, therefore alternator, is running.

Hugo's original post refers to the trailer battery needing occasional re-charging - a caravan type circuit seems the most suitable, particularly as the Discovery already has the 12S socket fitted.
12v supply to trailer via caravan socket - Hugo {P}
Thanks for all the responses. It looks like some 30A wire with the 10A fuses/trip switches on the trailer side - maybe in a little covered fusebox or something. A trip to a Lucas Auto electrical store mayb in order.

Ideally it would be nice to be able to operate the trailer from the 12S socket whilst the engine is running. That way I have the option of dispensing with the battery on the trailer and saving around 20K of weight. should I choose to.

It has spent most of the day connected to a trickle charger as the ram very nearly didn't make it with about a tonne on the back.
12v supply to trailer via caravan socket - Ruperts Trooper
What current does the electric ram need? The 12S socket will melt above 8A if you use a direct connection.
12v supply to trailer via caravan socket - Hugo {P}
Hmmm - good question I didn't think the socket was that feeble

I'll look in the morning. It could be higher than that.
12v supply to trailer via caravan socket - Ruperts Trooper
The normal cabling for the 12N plug/socket is 6A with a 8A earth, normal for the 12S is 8A with one 10A earth and another (for the caravan fridge) of 8A.

It shouldn't melt at 8.1A but 8A is the rated limit. A number of caravanners have experienced problems with 12S plugs and/or sockets starting to melt.
 

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