caravan battery wiring

Hi Bob,

While it sounds good in theory, there are many pitfalls to the "simple" system as described.

First of all, the aux connector on a standard 7 pin plug would only be good for ~10 amps. When you start your vehicle, the van battery is now in the circuit and you will fry your low amperage wiring.

Secondly, the voltage drop with small wiring will result in only ~12 volts at the van battery. A wet cell battery needs at least 13 V to get a half decent charge into it (alternator puts out 13.8V to car battery) and would never be fully charged.

I could go on with more issues in greater detail, but basically I could not recommend it as described. However, by simply using heavy wire (+ve and -ve, not chassis) and heavy duty connectors (ie. Anderson plugs), fuse it both ends and put a relay in to disconnect while starting, then you have the makings of a system to charge the van battery.

Cheers

Captain

Hi Bob and I’m sorry to contradict you again Captain but that is really bad advice about using the chassis as the earth return. Doing so is just begging for trouble and yes Captain I know you have done it that way and got away with it but it is not the recommended way to connect two batteries together, especially on a caravan.
Most caravans have a sub frame and the caravan body is bolted to the sub frame. This form of construction lends itself to poor electrical conduction all over the place. For low current uses like your blinkers and stop lights etc., you will probably get away with earthing them to the chassis but for high current situations, like charging a battery in the caravan from the vehicles alternator, if you want a proper charge then run twin 8 B & S cable from the front battery to the rear battery.
Using heavy cable, you will not only charge the rear battery at a higher voltage but it will charge quicker and as you have to run one cable from battery to battery, you might as well run twin cable as it will take you no longer and only cost you a few dollars more to guaranty you will not have any problems.
The one thing I do agree with Captain on is the use of Anderson Plugs on the battery wire between the vehicle and the caravan. A set of 50 amp Anderson Plugs will work a treat and note, Anderson Plugs are usually sold as single plugs and you need two.
One more point, you are far better off installing circuit breakers on the battery wire at each battery positive terminal. They will tolerate current surges but if the high current persists then they simply trip. If you use fuses, you will either be replacing them all the time or you will have to use large fuses and still might have problems.
It will probably pay you to install some sort of low voltage cut-out at the front battery so that you don’t end up being at a camp site for a few days and when you go to start your vehicle you find you have two low batteries. Hope this is of some help.
Regards

Hi again Bob H, are you wiring the whole van or just adding the battery. The reason I ask this is that you have not said whether you have fuses in the caravan already.
Regards

Bob,
Try the 12volt shop for information. They have a twin charge system for charging caravan & campervan battery systems. I have used this system in 2 vans and have had no trouble at all as the van batt gets a proper charge to the oulse stage. Connected to the vehicle via an anderson plug as mentioned with all wires of 6ml.
Sugest you contact the 12v shop. The ph no and E mail nos etc are advertised in 4b mags & van mags.
Regards Dodg