Can anyone tell me what I can use to hook to the trucks charging circuit to charge a battery in a camper? I want to hook into a 7 way plug already in the bed that will allow me to charge the camper battery but not draw down the truck's batteries. I was hoping for a simple fix without adding anything to the truck's charging system.

 

A battery isolator would be best. When the truck is running it will charge the battery in need and not hook the 2 together. This can cause 1 battery to go bad if the other is weak. The old way was to remove the power lead off the alternator and hook it to 1 of 3 lugs on the isolator the other 2 went to the batterties. when the key was off you could kill 1 completly and still have a good start battery. If you do not use a isolator you could use a starter solenoid to isolate the acessory battery and keep it from draning both.this is the way my 85 chevy came from the factory. Any RV shop should be able to sell you what you need for the job.

 

I bought my relay (looks just like the old starter relays) at an RV dealer. Cost me $16. Easy to hook up once you find the hot wire in the trailer circuit under the hood. That was fun.

 

If I use a relay, will it keep the batteries in the truck from discharging when using the camper battery?

 

Your battery will not run down. The way mine is connected is a seperate wire is run from the positive post of the truck battery through a circuit breaker than to the relay. From the relay the wire goes back to the battery on the boat trailer. The boat trailer battery is grounded to the trailer and the trailer is grounded back to the truck.

The wire that closes the relay is connected to some place that is engerized when the igniton switch is turned on. Thus when the ignition is on the relay is closed and feeding the trailer battery, when the ign, sw is off the relay opens isoulating the trailer battery.

The wire size should be about #10 and I used a 40 amp circuit breaker, as after camping for a while the camper battery could draw a pretty heafty load and the circuit breaker will give you some fault protection.

Hope this has been of some help.
Charlie

 

That's exactly what I was looking for. Thanks Charlie.

 

What Charlie did is just about exactly what I did for mine. The only difference is I used a 24volt contactor out of an old A/C condenser. I also used a 30 amp breaker too.
Tom