Q's on Isolators???????

I did a search already on the net, here, por, a few other sites but I still have some questions.
Tonight I picked up a second battery from one of my friends. It tests good at 850CCA's. I intend to use this in a dual battery set up. I know I will need to run an isolator but am having difficulty choosing one. I found a new one for 15 bucks but its only like 30 amps... So my question right now is will that isolator be enough or am I going to need something more? Other items that might factor in are:

1) I am still using the factory alternator. I intend to up grade to another alt. this spring that is about 140amps.
2) I am running driving lights and intend to install a second set of offroad lamps.
3) The XJ has medium power stereo system that isnt drawing a bunch, but I do intend to install a couple amps this coming spring. Right now its only like a 200watt system.
4) I will be installing a CB soon.
5) We will be upgrading some of my systems wiring. I will use a heavier gauge wire and relays to draw power directly from the battery (headlamps, door locks, etc.)
6) Have no thoughts on buying a winch.

I want to make this as cost effective as I can. My first item to buy is going to be the isolator. So I need to know which one of proper for the application. thankx

While an isolator will do the job, I have found that using an industrial solenoid is cheaper and better. You should be able to score one for about $10 at a "truck supply" shop - but make sure to ask for one with a 100% duty cycle.

You'll wire it up so that the solenoid will close with the ignition in the "ON" position - that way, you can wire up your accessories, lights, radios, and whatever to the deep cycle directly and use them with the key OFF or in ACC without digging into your starting battery.

Typically, the solenoid will work for up to 100A - you can find higher ratings if you are willing to wait a couple days.

Another place to try is Allied Electronics (I think) - look them up at www.alliedelec.com. I seem to recall seeing solenoids like this in their catalogue, and they are all over the place. I think they carry solenoids up to about 200A with a 100% duty cycle, so that should work for you.

How high should you go? I'd take the peak power output of your alternator, drop about 30A for essentials, and add about 15% of what's left for overage. Or, you can just take your alternator rated output and use that straight over (use the next higher, if you are in between.)

Either way, I'm sure you'll find the solenoid to cost quite a bit less than the solid state isolator, and I find them to be quite reliable. I've used them when rigging electrics on work trucks - while I've often included a spare in the onboard kit, I've never needed it...

5-90

If you go the isolator route, you will need one rated same as or higher than the alt output. I think the iso is the best way to go. I put a solenoid between the batteries so I could turn on the 2nd batt when I wanted to, ie winching, other batt was dead, etc. The isolator lets you charge both batteries but doesn't let them drain back through the charging system. Example...the very first night I got my jeep back on the road after 4.0 swap, 2nd battery, HO alternator, etc., the alt was bad and it drained my battery dead overnight. I come out for work in the am and nothing...flip the switch to turn on #2, and she started right up. It worked well for me. Downside, a 130A isolator was over $100.

HTH.

Hamy.