Camper trailer Spare Batt Charging

[sambo2222]

My Oldies have one of those off road campers with a battery in it to run lights andd water pump ect. The question is how do I wire the trailer batt up to the car to charge of the car's alternator or batteries.
It is a late model Pajero with dual batteries. The trailer is also fitted with anderson plug for brakes. Any help would be greatly appreciated.

[CRUSHU]

Sometimes you see trailers where instead of using a trailer axle, they use a car diff. If you did use one, you could run 1 or 2 alternators off the pinion of the diff. Whenever the trailer is in motion, it is charging the battery. It wouldn't help much if you were setting up camp for a while, but if you were moving every day or two....

[sambo2222]

unfortunately it is one of those flash ones. No diffs. The dual battery in the engine bay gets charged so I don't see the reason I can't do the same with the trailer battery. I just don't know how

[drivesafe]

First off, how thick is the wire for the trailer brakes. You might be able to move the brake wiring to the trailer plug.

Or you can just run new cable from the vehicle’s Auxiliary battery to the trailer’s battery and fit another set of Anderson plugs, only this time use a different size so that there is no mistake when connecting all the cables.

Next, no matter how you decide to connect the cable between the vehicle and the trailer, you are going to have to run some heavy cable from the vehicle’s battery to the trailer’s battery and it will have to be at least 10mm2 or you will take for ever when trying to charge the trailer battery. That’s both a positive cable and a negative cable.

You will also have to fit circuit breakers at each end of the positive cable, as close as practical to the positive terminal of each battery.

That’s the basics of it and if you set it up this way, while the trailer and vehicle are connected together, the camper can use some of the power from the vehicles auxiliary battery.

Cheers.

[sambo2222]

thanks drivesafe. Sounds good. If I connect 10mm2 cable between the aux batt on ther car and the batt on the trailer won't they be in parrallel. Hence a big inrush of current when the trailer gets connected to the car especially if the trailer batt is pretty flat and the car battery is fully charged. Is that what the circuit brekers are for or for short cct protection?

[drivesafe]

Hi sambo2222, if you connect the trailer to the vehicle while the motor is off and depending on the types of batteries you are using and the amount of difference in the state of charge in the batteries, there will be a current flow between the highest charged battery to the lower charged battery but even in the worst case it will be measured in amps not tens of amps.

But, as will be the case most of the time, when you connect the trailer to the vehicle while the motor is running, then the alternator voltage is going to be way above the vehicle’s battery voltage and as such, there will be NO current flow from one battery to the other.

The alternator will be providing voltage/current to both batteries.

Cheers

[sambo2222]

aaaaaahhhhhhhh. The light finaly comes on. Thanks heaps for the help. Will connect up tomorrow and see how things go.