Electrical Guru's: Dual Battery Question....

[lump-dog]

I'm rounding up all the items needed for a dual battery setup on my 2001 f150 supercrew.

Question 1:
Do I need an battery isolator gizmo? Or is a 4 postion switch all I need? (BATT 1, BATT 2, BOTH ON, BOTH OFF). Pros, cons, and an explanation of why would be greatly appreciated.

Question 2:
While searching for a battery switch, I came across a
BLUE SEA ([URL="http://www.bluesea.com/product.asp?Product_Id=31165&d_Id=7458&l1=7458&l2=) switch that has an Alternator Field Disconnect feature that will protect an alternator with an external regulator from damage in case the switch is inadvertently turned off while the alternator is producing power (I guess that's bad!?). This feature requires me to cut into the alternator field wire, and run it through a couple lugs on the switch. My alternator has what I would call an "external" regulator, since it is attached to the back of it. However, it doesn't appear to have a field wire that I can get at, it seems it is "internal". Anyone have a direction for me on this?

[FlyHiFlyLo7]

Maybe there is a Bad *** alternator you can get from a car audio shop that solves this issue. Like Phoenix Gold type of deal. The car audio guys really have this problem wired. (no pun intended) Maybe go to your local car audio shop and see what they do on Fords.

[Superfab]

Watch out for the battery switches. I've had different ones fail. The solution I'm using in the new race car is 2 Flaming River "Big Switch" on-off switches. The contacts are rated at 250 amps continuous and 2500 amps surge. With this setup I can add a battery to the circuit and remove the other one after without shutting the motor off or hurting the alt. You can turn on the second batt. when needed for misc. circumstances. Charge wise, you can rotate the batteries so they are allways charged. This way you don't effect the alt. wiring in any way. If you switch off both the batteries while the thing is running you will smoke the diodes in the alt. !

[gwm]

On my chase truck and hauler I run a big relay just like on a motorhome. It's wired so the batteries are connected during normal operation and both are charged by your alternator without modification. The second battery is an optima blue top and runs the race radio and other things I might use when the truck is off. I have a toggle switch powered by the aux. battery to power the relay just in case I need an internal jump.

Two things: make sure the relay is run by keyed power and stay away from isolators. It's cheaper and a lot more reliable just to run a relay.

(Oh, and make sure it's the right relay. A stereo or motorhome shop can hook you up. Starter relays are not made for continuous use.

[endeavor]

Personally, I think an isolator is the way to go. These guys are awsome -- spend a little time on their website and you'll learn a lot about dual battery setups.
http://www.hellroaring.com/

[azfabguy]

I have used the relay setup for years on big stereo show cars and had no problems.