I'm going to be doing some projects in my car that are going to have some larger power requirements, and I don't think one battery will be able to handle this.

The question might be better answered in the car audio forum, but figured I would try here first.

What I want to do is put a second battery in the car, but to do that I suspect I'm going to need a bigger alternator. I'm pretty sure my amp draw will be more than a stock type can handle.

My questions are one, anyone have some suggestions on good alternators for this purpose? Something capable of 140ish amps would probably be sufficient.

Second, the wiring of the second battery. Can I ground it to the block with the other battery and just run a line to the same post on the alternator as the primary battery for charging it?

I have even entertained the idea of installing a second alternator in the car in place of where the smog pump used to be since I removed it. Would that be a better solution than charging two batteries with one alternator?

 

There are a few options. I have a diode type battery isolator which allows my alternator to charge each battery, but maintain separate circuits. Also, I had my stock alternator rewound at a local alternator, generator and starter service store so it outputs 140 amps. Most RV or marine stores will carry battery isolators, most for a two battery setup will only have 3 posts, the CS130 alternator needs one with a 4th post for excitation.

Here is a simplified drawing similar to the isolator system in my car, it doesn't show the 4th post required but the rest is accurate. My second battery is in the back with the system (in the lockable compartment) and grounded to the chassis by the hatch release.



Another option is to use a combiner/isolator which will allow you to use both batteries for starting and separate them while maintaining charging abilities from the alternator. I've heard good things from this site for that type of application..

http://www.hellroaring.com/battery1.php

http://www.hellroaring.com/Basic%20Aux%20Audio.php

 

Thanks for your reply!

I for sure don't want to use both batteries for starting. In fact that is one of the reasons I want to go to a second battery. One of the projects I'm going to be doing in my car is a carputer, if for some reason it doesn't shut down properly and stays running when I turn the car off, I want it be on an isolated battery and not kill the cranking battery.

It looks like essentially the battery isolator is just switching between the two batteries allowing the alternator to charge one battery at a time?

The placement of my 2nd battery I haven't decided fully yet, but I think I'm going to move the charcoal canister on the front driver's side and put it there.

Was getting your alternator rewound cheaper than just buying a bigger alternator, or was it simply mounting concerns that caused you to go in that direction?

 

Would love to see what you are planing that is going to pull 50+ amps constantly...

I built IASCA Competition vehicles back in the day and rarely went to a dual battery setup. and generally the only cars that got the dual setup were true competition vehicles that never saw the road.

a 120-150amp alternator, Optima Yellow Top and appropriate capacitors is more than enought for 99% of the cars out there.

 

Well my amp is already pulling 30 amps on average. As I said I'm planning to add a carputer to my car that is going to pull another few amps (Probably 5 to 10 amps). And there may be some other stuff that will collectively add up to another 5 or 10 amps.

Yes a 120 to 150 amp alternator would probably be enough on one battery, but as I said in my last post, one of my concerns is the carputer not shutting down correctly and draining the battery. Better to have it on it's own battery system and not effect the cranking battery so that I don't get stranded somewhere with a dead battery.

As for the Optima yellow top, no thanks. That is one of the most overpriced hunks of junk I've ever used before. I killed two of those batteries within a year in a truck I had before when running a larger amp and a few subs, even while using a 2 farad capacitor. After killing those two I put in an Advanced brand gold battery and it ran for 5 years before I got rid of the truck.

 

No switches, the diodes keep the two batteries isolated from each other during charge and prevent parasitic draw from one to the other.

It was more a convenience thing than anything else. Cost was about the same as a new alternator, but the shop was local and turnaround time was quicker than ordering a new one. Stock case was a bonus but 140 amps is all it can do for its size. Warranty is the same as new also.