#12125  by Troppo
 Mon Jan 18, 2010 12:44 pm
I have just bought a caravan, and have been inspecting it all before I head off for an indefinite period of traveling.
It is a UK import caravan, and has had the towing plug changed to the flat 7 pin type, which is all good. Upon reading the manual I noticed that it stated it had 2 plugs, one for the lights (indicators and so forth) and the other plug to power the fridge, interior lights and charge the battery from the car. Sure enough, when I had a good look under the drawbar I found a 7 pin round type plug, and tracing the wiring back found it connected back to the caravan battery, the fridge and the interior lights.
Now, obviously my tow car does not have a second plug to power these accessories, and so I want to wire up another plug on the car.
Thus my question...
Does the feed to charge the caravan battery need to come from the alternator, or can I just use a 12v feed such as the feed to power the fridge and the lighting?
The fridge wiring is fused in the caravan, but I would install fuses for the car wiring too. How many amps fuse should be in the charging wire?

And, where can I get the old type round 7 pin plugs from? (I was thinking of changing it to flat plug but like the idea of a different plug type for powering the living section of the caravan.)

 #12126  by Nut17
 Mon Jan 18, 2010 1:11 pm
Hi Troppo,

I would suggest that you convert to the heavy duty 12 pin flat plug which will accommodate all the connections. You will need fairly heavy gauge wire to power the fridge and to supply any useful amount of current to your caravan battery. Charging voltages are critical and voltage drop from undersized wiring from your tow vehicle to your van battery will result in very little charge getting through.

I would suggest that you take advice from a qualified auto electrician and don't skimp or make any compromise with quality.

I have attached a pic of my 12 pin plug and also shows the 50 amp Anderson plug that is wired back to the Jeep battery through a voltage sensitive relay using very heavy cable. (only sends power down the wires when engine is running) This heavy duty wiring and plug is dedicated to charging the caravan battery bank, 2X 100amp AGM deep cycle units.

PS sorry about picture quality, I should have selected the macro setting on my camera- and my dodgy aged eyesight didn't notice the poor focus.

Cheers Chris
001.jpg (52.35 KiB) Viewed 1881 times
 #12201  by Troppo
 Wed Jan 20, 2010 10:31 am
Thanks Chris for the photo of your plug. So your anderson plug just comes straight from the battery, not from the alternator?
I think I'l keep the 2 plug setup, since that's how it came from the factory.
Can anyone answer my question, can I send a 12v feed to the battery in the van to charge, or does the wire need to come from the alternator? The van has a switch to isolate the charging circuit, so it can be turned off once the vehicle is stationary.
 #12209  by WoodyZ
 Wed Jan 20, 2010 2:05 pm
Short answer - Straight from the battery.

Longer answer - I would be reluctant to rely on a manual switch to isolate the two systems, you need to fit either a system which senses that the tow vehicle engine is running and this enables the power to flow between the two battery systems, or better, an isolating sensor that will detect the two voltages and only connect when the voltage in the tow vehicle battery is higher than the van and the engine is running.

There are a few different ways of achieving the desired result and the best person to talk to would be either an auto sparkie who has has some experience in caravan or motorhome hookups or a motorhome/caravan maintenance company with in house sparkies.
 #12249  by WoodyZ
 Thu Jan 21, 2010 7:08 am
If you happen to forget to throw the switch, you can easily end up with two flat batteries. Not really a problem in the van, but not having enough to crank over your tow vehicle could be seriously problematic.

All it takes to forget is to have a minor interruption while working through your standard set-up procedures, you don't even need to have a dodgy memory.
 #12250  by releivingbob
 Thu Jan 21, 2010 8:50 am
i would use the plug chris has, we have used them extensively on our reefer units to charge our taillift batteries.

and as neil says use a voltage sensing relay that will only send power down there when the tow vehicles engine is running or the tow vehicles batteries are over say 13.6 volts
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