12 volt from car to deep cycle battery in caravan.

Hi Johno

I am no electrician but the way it was explained to me when I asked a similar question to yours was that in order to charge the van's batteries, I needed an Anderson Plug fitted to the towing vehicle. This then charged the van batteries whislt towing.The Anderson Plug is totally separate to the 7 point flat plug that you have installed. Google "Anderson Plug" and you will find photos, wiring instructions etc.

All the best
Snolly

Johno59

I would hope your last X trail had a large current capacity cable from your car battery to an Anderson plug at the rear of your car which had a socket wired to the van battery using similar cable.

These plugs are used because none of the seven pin flat plug cables will carry the current needed over the length of cable from your car battery to your van battery for direct charging using the car alternator

You can use a DC to DC charger and use the seven pin socket aux cable to power that charger in the van.

A solar controller is also a good idea to manage which of the charging sources is best at any given time, ie alternator when car is running and solar panel when not.

If you know how the solar cell is connected then you should disconnect it and then You only need to connect the car to the van with the seven pin plug connected and the car running to see with a volt meter if that socket is providing any power to the van battery, I doubt it.
Then disconnect the car and reconnect the solar cell and check again.

If that's all good then you will be wiser when talking to the auto elec t ohave your anderson plug fitted

Enjoy

Sorry, 12 point plug should read 7 point plug johno

Hi Johno,

Super cheap now do an "Anderson Plug" Kit for around $60.

Easy as to install and no messing with wiring up the Anderson Plugs ($35.00 per pair on their own) and the kit includes 7 metres of 6BS cable.

Works for us when keeping the camper batteries topped up.

I do need to check on the answers to a question I asked back in March, regarding battery controllers.

A standard alternator may stuggle to supply the required power, an after market, high output alternator should cope well and give you little trouble.

Cheers,
Wayne & Sally.

Johno,

The standard wiring to the 7 pin plug at the back of the vehicle is NOT adequate for charging the battery in the van. As others have said, you will need a heavy wire, preferably a pair of heavy wires to carry the current without excessive losses.

You will need

1) a controller fed via a big fuse (at least 30 amps) from your vehicle battery to connect the charging current to the van when (and only when) the engine is running.
2) heavy cable (say 6 B&S) from the controller to the van, using an anderson plug at the towbar to allow disconnecting.
3) the cable should connect to the van battery through another big fuse mounted right at the battery.

You might get away with simply running one cable, to carry the positive side of the circuit, with another cable connecting the negative side of the battery to the chassis of your vehicle. Far better though to run a cable all the way from van battery negative to vehicle battery negative. You do not need fuses in this negative line.

One more essential - PLEASE read Electricity for Camping which was specifically written to help people in your position. It provides answers to many of the questions you've asked, including the above, and lots more you haven't asked yet!

Cheers

John

Johno 59
Gee I wish you had mentioned the 12 pin plug on the car in your first post as we all would have advised differently.

The 12 pin plug and sockets can provide the power required due to slightly larger cable used in them however most people would recommend a seperate circuit for battery charging and just use the 7 pin plug and socket for the usual lights on the van.

As your new car does not have the 12 pin then my advice is have an auto elec fit a seperate anderson plug circuit.

Cheers

Thanks everyone for your great advice. I will digest it all today. I THINK i HAVE LEARNT MORE ABOUT BATTERIES,CURRENTS ETC IN 2 DAYS THAN A LIFE TIME!! With due regard for all the advice, I do remember the guy from Jayco telling me when he installed the existing setup it would take many long hrs of driving to charge the battery.( A case of little knowledge is dangerous would't you think?) thanks again! PS I just wonder how many 100's of vans leave the caravan outlets,with owners thinking their van batteries are being charged correctly! I know they do lots of them in our local outlet.

This is a typical example of how limited the knoweledge of 12 volts electrics generally is and the preconcieved ideas people have.

It is indeed possible to charge a battery in a trailer thru the standard 7 pin flat or round plugs....in fact it is an application mentioned in the standards.....but there are limitations.

The pin for reversing lights is hardly ever used, so that is commonly used for battery charging.

the limitation is that the charging will be slow, but if properly done possibly not as slow as some would expect.

The rated current of the pins in the trailer plugs is arround 15 amps, it is certainly possible to connect cable capable of carrying 15 amps to a trailer plug.

By designing for specific voltage drop and not minimum voltage drop it is possible to select a wire that will self limit the charging current not unlike charging a battery thru a fixed resistor...of course appropriate fuses both ends.

So it is reasonable to have a nominal charging current of around 10+ amps delivered to the trailer battery thru the standard trailer plug.

If the battery in the trailer was only running some lights and the radio, this would be more than adequate particularly if the vehicle was driving 4 to 6 hours a day.

No dual battery controller required, very cheap and viable.
If you want to stop the car battery being drained at night pull the plug......but most of us would do that when we set up for the night anyway.

And if the trailer does not house a DC powred fridge or other heavy drain items, perfectly fine and reasonable...such as a traveler that uses ice like almost all of us once did, or someone who runs a fridge on LPG like untill quite recently was the norm.

OR for those who keep the fridge in the main vehicle and are simply towing a camper or small caravan a most eligant solution.

Seriuolsy charging thru the standard trailer electrical connection should not be dismissed as rough or inadequate.

If however you have heavier drain items in that trailer or you require heavier chaging capacity, an heavier connection and wiring is necessary.


cheers

bantom, Thanks, Your advice makes a lot of sense! According to an auto electrician I spoke with today, the existing set up does charge up the Battery A LITTLE and does take a fair amount of driving. BUT as you say, with very little 12 volt power required ( ie 1 or 2 led lights, everything else powered by Gas or rechargable batteries) I might get by, Although it does make sense to harness as much charge as you can from the vehicle when traveling. Do you have any idea of the cost to have this work done by an autoelectrician? thanks johno

Gidday Johno,

Here are a few photos of the install I did on my caravan and Troopy.

I used 10 sq mm. double insulated flex and ran it in rhino electrical conduit under the troopy and in heavy duty flexible conduit on the van. I made all the conduit clips under the troopy from light gauge stainless and secured the conduit above the chassis for protection. I made up nuts that I could place in the chassis through existing holes.

The anderson plug sits in a hole in the Kaymar bar that was already there and that keeps it away from being damaged.

The cables are are protected both ends with circuit breakers and on the bottom of the van circuit I mounted a diode to stop any back feed to the vehicle.

I have taken some photos as they are worth a 1000 words.
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I can't remember the cost but I did all the work myself. The cable was welding flex.

RA.

Rockape, Thanks for the pics,much appreciated!! johno

I have to worry about connecting the car battery and alternator back to the caravan battery via a fuse and cable capable of 50A. The car battery is capable of supplying much more than 50A when cranking the starter, therfore, I would like to know what current a totaly flat caravan battery will draw from the car when connected?
Dual battery isolators seem to be rated at 100A and 150A. If they are the maximum currents that can be expected then you'd need a big pocket full of replacement 30A fuses.
With 50A wiring the only way I'd like to see the two batteries connected is via a DC-DC charger which will limit the current to the rating of the charger.
Can someone that is a true expert enlighten me?