Dummy needs help !!

[Steve Curren]

I have a trailer with the deep cycle battery in the nose box, I want to put another battery in the rear. My question / concern is how I can wire the rear battery to the charging system from the tow vehicle without the other battery pulling power from it. I am not sure if it would suck the juice from either one but I want to hook it up corectly.
Thanks,
Steve

 

[DaveInDenver]

Do you need to be able to selectively switch the batteries? If not, you can isolate the two batteries with a pair of diodes. Feed the +12V to the both diode anodes and connect one cathode from each diode to the + side of the battery. Each will get current only from the common feed, not from the other battery. You will get a slight voltage drop across the diode, up to 0.7V but could be as low as 0.3V. Depends on the type of diode you pick. What's your budget for the project?

 

[Steve Curren]

I don't imagine I need to switch the batteries, I just want to be able to charge them both without taking power from the other. Now for the important quesiton what's a diode? I have no idea how much this would cost but I would like to keep it as low as possible yet do a good job. I would like to get the diode that restricts the voltage flow the best.

 

[articulate]

To make it simple, I'd call Wrangler Northwest Power Products and talk to Steve. He'll be able to talk you through it and suggest a product or two.

Hope it helps.

 

[DaveInDenver]

To make it simple, I'd call Wrangler Northwest Power Products and talk to Steve. He'll be able to talk you through it and suggest a product or two.

That's probably the right answer here. Think of a diode as a semiconductor check valve, current flows one way, but is blocked from flowing back.

 

[Steve Curren]

Guys,
Thanks for the info, I now have a good idea what a diode is and I am looking up Northwest Power Products.

Steve

 

[eugene]

yep, its a one way valve. Surepower makes a lot of battery isolators which are a pair of diodes stuck in an aluminum case. You have three terminals, one for input and one for out to each battery. The diodes prevent current from flowing from one battery to another.
Napa sells surepower gear with their name on it. You need to size the isolator large enough to handle the load, for example for my 105A alternator I used the 120A isolator.

 

[Steve Curren]

Thanks, I looked up the Surepower and have fond one I believe that will work.
If I was to get a 120 A isolator how can I determine the output of my alternator?

Thanks,
Steve

 

[eugene]

The alternator output should be marked on the alternator or on the specs for your truck somehwere.

 

[articulate]

Steve, the output on the OEM Jeep Rubicon (through 2006) alternator is 117 amps.

 

[Steve Curren]

Gents,
Thank you ever so much for your kind assistance. I have the battery installed and will order a 120Amp Isolator, one question more if you please. Can I use a common ground for both the batteries without messing up the works once again??

I owe a drink to all, I will be at Pyramid Lake and you can collect there.

Steve

 

[DaveInDenver]

Gents,
Thank you ever so much for your kind assistance. I have the battery installed and will order a 120Amp Isolator, one question more if you please. Can I use a common ground for both the batteries without messing up the works once again??

I owe a drink to all, I will be at Pyramid Lake and you can collect there.

Steve

Yup, all the negatives are connected together. You don't have to physically tie each ground wire together, taking a ground cable to a common thing like the frame is fine.

 

[Steve Curren]

Thanks, I will just tie the negative posts of both the batteries to the ground coming from the Jeep..
Once again I am in debt to those on Expedition Portal, great group of folks.

Steve

 

[eugene]

Check the surepower instructions and see if you need the isolator with the 4th pin. Some alternators require it, like my GM.

 

[Steve Curren]

Thanks for the heads up, I have a Jeep and it looked like the Chrysler products didn't. I did see a certain type of GM product that was different.

Steve