12 volt from car to deep cycle battery in caravan.

Hello Everyone, Someone with more knowledge of electrics may be able to advise me. I have a deepcycle battery in the van and a solar panel to top it up. My previous x trail was wired to charge the battery in the van whilst travelling. I now have a new 2008 x trail with a 7 point flat plug but am uncertain IF the van battery is being charged by this new vehicle. Is there some simple way of testing it? OR do I have to travel with the van hooked up and then run a voltmeter over the batt terminals to see if its being charged. ( I guess its a fairly simple check for an auto electrician, but thought I might try and save some $$$ thanks everyone johno
Back Expand Un-Read 0 Moderator

Reply By: SNOLLYGHOSSTER - Saturday, Apr 28, 2012 at 19:19

Saturday, Apr 28, 2012 at 19:19
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

AnswerID: 484468

Follow Up By: Member - Boo Boo (NSW) - Saturday, Apr 28, 2012 at 19:45

Saturday, Apr 28, 2012 at 19:45
G'day Johno

Basically you need to run fairly thick wiring from the battery to an Anderson plug at the back of your vehicle.

I use wire that has a dia almost as thick as a skinny little finger (if that makes sense).

You also need to put a 50amp in-line fuse close to the battery.
to the car
I have found it easy to run the wire under the vehicle and attach both wires with cable ties.

Probably a good idea to put the anderson plug near the 7 pin plug.

You then need to to run wiring from the caravan battery, no fuse required, to the front of the A frame of the van. Leave enough slack to allow for the van to turn and connect to the anderson plug on the car. Simple!

I,m not an electrician and some one may have a better way of doing it.

FollowupID: 759743

Reply By: Von Helga - Saturday, Apr 28, 2012 at 21:13

Saturday, Apr 28, 2012 at 21:13

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

AnswerID: 484490

Follow Up By: johno59 - Saturday, Apr 28, 2012 at 21:49

Saturday, Apr 28, 2012 at 21:49
Thanks everyone, There is something strange here that I don't understand. When I had the deep cycle battery installed by Jayco, all the wiring was done including the installation of a 12 volt cigarette socket. I was told by Jayco that all I had to do was connect the 7 point plug on the van to the 12 point flat plug on the car and the battery in the van would be charged whilst towing it. There was no mention of an additional and separate Anderson Plug,and I just assumed that the 7 point plugs on the van and the vehicle somehow were wired to carry the currents needed to charge up the van battery!! I also forgot to mention that the van battery can be charged by simply connecting 240 volt power to the van. thanks johno
FollowupID: 759765

Reply By: johno59 - Saturday, Apr 28, 2012 at 21:55

Saturday, Apr 28, 2012 at 21:55
Sorry, 12 point plug should read 7 point plug johno
AnswerID: 484496

Follow Up By: johno59 - Saturday, Apr 28, 2012 at 22:10

Saturday, Apr 28, 2012 at 22:10
Von Halga, I think the confusion is with the charger. The van must have a built in charger, otherwise how is it possible to charge up the van battery using 240 volt power? Given that, I assume the 7 point wiring and plugs on the van and vehicle have an auxillery wire as you suggested. This would explain everything including the jayco technicians advice. What do you think? Does this now make sense? ( As you can gather, my electrical knowledge is not good) ha ha thanks johno
FollowupID: 759768

Follow Up By: Member - Boobook - Sunday, Apr 29, 2012 at 09:22

Sunday, Apr 29, 2012 at 09:22
Johno, I recently looked at a Jayco's wiring for the battery and fridge. It was about 8 years old.

The way Jayco did it then ( not sure about now) is that they ran a wire from pin 2 ( aux / reverse) to the fridge, and via a diode to the battery.

Provided your car is wired to supply 12V to pin 2 ( and not reverse) this will allow the car to charge the battery as well as power the fridge. The fridge won't run on 12v when the car is not connected. The problem with this, is that the battery will never get a full charge whilst running from the car. Not ideal but it means that it will work to a point without an additional Anderson connector or a 12 pin plug. it would probably do if you just have 12v lights in the van but if you want to power anything else you will run short of power quicker than necessary.

There was also a 240 v charger that was quite a large panel with about 6 fuses in it for charging from 240V. It was under the seat.

FollowupID: 759798

Follow Up By: johno59 - Sunday, Apr 29, 2012 at 09:54

Sunday, Apr 29, 2012 at 09:54
Thanks Boobook', I also have a solar panel to top up the battery. The information you have provided is pretty much what we were told by Jayco. We have led globes in the van and run only 1 or 2 when needed, maybe 1hr a day. Also we use a rechargable Coleman led lamp. They are excellant and give hrs of lighting. There is a 240 volt charger beneath the seat and fuses as you say thanks jkohno
FollowupID: 759803

Reply By: Wayne's 60 - Sunday, Apr 29, 2012 at 03:36

Sunday, Apr 29, 2012 at 03:36
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.

Wayne & Sally.
AnswerID: 484506

Follow Up By: Member - Boobook - Sunday, Apr 29, 2012 at 09:34

Sunday, Apr 29, 2012 at 09:34
Wayne, FYI you can get a pack of 10 genuine Anderson plugs on ebay for $20. You should never pay more than about $6.00 ea.
FollowupID: 759799

Follow Up By: johno59 - Sunday, Apr 29, 2012 at 09:56

Sunday, Apr 29, 2012 at 09:56
Paid $ 10.00 for a set on Ebay johno
FollowupID: 759804

Reply By: Member - John and Val - Sunday, Apr 29, 2012 at 07:36

Sunday, Apr 29, 2012 at 07:36

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!



J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein

Lifetime Member
My Profile  My Blog  Send Message

AnswerID: 484511

Follow Up By: tojofixa - Sunday, Apr 29, 2012 at 08:06

Sunday, Apr 29, 2012 at 08:06
The simplest way to check if your van battery is bieng charged from your car is to connect your van to the car as you normaly would when travelling, then check the battery voltage in the van with the car not running, using a good quality multi meter, then start the car and run at a fast idle and recheck the voltage at the van battery. You shoud get an increase in voltage to around 13.8 volts or better.
Hope this helps,
Regards, Derek.
FollowupID: 759794

Reply By: Von Helga - Sunday, Apr 29, 2012 at 09:21

Sunday, Apr 29, 2012 at 09:21
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.

AnswerID: 484518

Reply By: johno59 - Sunday, Apr 29, 2012 at 09:29

Sunday, Apr 29, 2012 at 09:29
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.
AnswerID: 484519

Reply By: The Bantam - Sunday, Apr 29, 2012 at 12:13

Sunday, Apr 29, 2012 at 12:13
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.


AnswerID: 484529

Follow Up By: The Bantam - Sunday, Apr 29, 2012 at 12:18

Sunday, Apr 29, 2012 at 12:18
BTW...you should have both ends of the connecting cables fused near the batteries.

The battery in the trailer makes the connection on the drawbar live and a posible source of a short.

SO the cable from the trailer battery to the drawbar should have a fuese or a breaker in it as well asn the supply from the tow vehicle battery.

FollowupID: 759817

Reply By: johno59 - Sunday, Apr 29, 2012 at 14:02

Sunday, Apr 29, 2012 at 14:02
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
AnswerID: 484537

Reply By: Rockape - Sunday, Apr 29, 2012 at 14:51

Sunday, Apr 29, 2012 at 14:51
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.
Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

Image Could Not Be Found

I can't remember the cost but I did all the work myself. The cable was welding flex.

AnswerID: 484542

Reply By: johno59 - Sunday, Apr 29, 2012 at 21:04

Sunday, Apr 29, 2012 at 21:04
Rockape, Thanks for the pics,much appreciated!! johno
AnswerID: 484570

Reply By: lesterb - Monday, Apr 30, 2012 at 14:40

Monday, Apr 30, 2012 at 14:40
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?

AnswerID: 484636

Sponsored Links