Dual Batteries on an older truck.

[mkitchen]

I am working on my 71 F 250 with the intention of having it for a secondary expedition vehicle. The engine and drivetrain is pretty much good to go (knock on wood). I do want to upgrade to Alcan springs but that can wait.

Right now I want to put in an additional battery. The truck now has G27F battery and I want to put in another battery of the same or similar in size, but with an isolator so I don't over use both batteries. There is plenty of room under the hood for the second battery. I would like to access the second battery as needed for starting if needed. I am not too worried about expense, more concerned about good quality and not too difficult to install.
Mikey

[MakersTeleMark]

http://bluesea.com/category/2/productline/overview/329

[benjamin]

http://www.wranglernw.com/ShowCatego...ategoryid=1008

[rusty_tlc]

When I wire the 12V circuit for a trailer connection (the same thing as a dual battery set up with the battery located in the trailer) I use a regular old solenoid. These mechanical relays are incredibly robust, essentially the same design as an old Ford starter relay. They also have a very low "ON" resistance. If one does fail you can get a replacement at any RV parts store in the world. At less than $30 they are, IMHO, the best bang for the buck.

The down side is you have to use jumper cables to self rescue, but you probably carry a set of those to help out others anyway right? My opinion is you should maintain your truck electrical system well enough that needing a jump is the exception, not something you would spend time and money on hard wiring switches into your electrical system to accomplish.

[rusty_tlc]

You will also need a thermal breaker with whatever isolator you choose.
I like this type with the rubber insulating boot. This will cost less than $10 with the boot.

[Wyowanderer]

When I wire the 12V circuit for a trailer connection (the same thing as a dual battery set up with the battery located in the trailer) I use a regular old solenoid. These mechanical relays are incredibly robust, essentially the same design as an old Ford starter relay. They also have a very low "ON" resistance. If one does fail you can get a replacement at any RV parts store in the world. At less than $30 they are, IMHO, the best bang for the buck.

The down side is you have to use jumper cables to self rescue, but you probably carry a set of those to help out others anyway right? My opinion is you should maintain your truck electrical system well enough that needing a jump is the exception, not something you would spend time and money on hard wiring switches into your electrical system to accomplish.

Ditto, except that you need a continuous duty solenoid, not a regular Ford solenoid. They don't last long in continious use. You can buy the right one at an RV parts store; I think I paid fifteen bucks for my last one.
Great suggestion otherwise.

Connect the camper battery to ground and to a thermal breaker, the thermal breaker to the solenoid, and the solenoid to the main battery. Ground the solenoid and connect the exciter terminal to switched on/off 12V power (like your coil wire) and you're done with the charging system. You'll want a quality fusebox like the one made by BlueSea to protect the wiring between the aux. battery and the camper/load, and you're done.

[rusty_tlc]

Ditto, except that you need a continuous duty solenoid, not a regular Ford solenoid. They don't last long in continious use. You can buy the right one at an RV parts store; I think I paid fifteen bucks for my last one.
Great suggestion otherwise.

Connect the camper battery to ground and to a thermal breaker, the thermal breaker to the solenoid, and the solenoid to the main battery. Ground the solenoid and connect the exciter terminal to switched on/off 12V power (like your coil wire) and you're done with the charging system. You'll want a quality fusebox like the one made by BlueSea to protect the wiring between the aux. battery and the camper/load, and you're done.

I didn't word that very well, I wasn't suggesting using a Ford relay. Thanks for pointing out how that could be misunderstood.

[mkitchen]

If I do use the solenoid, would I be running battery size wire from the battery to the thermal breaker and then to the solenoid? My appologies for my ignorance.
Mikey

[rusty_tlc]

If I do use the solenoid, would I be running battery size wire from the battery to the thermal breaker and then to the solenoid? My appologies for my ignorance.
Mikey

Just a large enough wire to carry the max expected charging current. I use #10. I'm wiring from the battery all the way to the rear bumper, a heavy wire has less resistance and thus a lower voltage drop*. For a short run you could probably use #12.

Anything you wire off the aux battery will need the correct size wire, #2 for a short run to a winch for example. But sizing wire is a whole topic in itself.

*You want to keep the voltage drop low to reduce heat in the wire;
P=IV, the power will be dissipated as heat.