Dual Voltage

[48mirage]

Finished installing a dual voltage system today. I bought a GM 10si alternator from the pick and pull and rebuilt it with a 12 volt Positive ground rectifier. Installed 2 Optima 6 volt batteries in series and then tapped off of each one for my needs. Car still operates on 6 volt, starter and headlights now on 12 volt. I will be adding a 12 volt radiator fan in the future. For a modern radio I will still need one of those fancy little inverters but I'm happy with the outcome so far. I know there are some that have told me that I will end up overcharging the outside battery. We will see. I wonder if the positive ground polarity affects this.

http://s262.photobucket.com/albums/ii86/jacobsheir/?action=view&current=DualVoltage2.jpg

http://s262.photobucket.com/albums/ii86/jacobsheir/?action=view&current=Dualvoltage.jpg

[martybose]

The problem has nothing to do with the positive ground, it's because you can only have one of the batteries set up as the ground reference for the 6V system, but you are using a 12V alternator to charge both batteries in series. There isn't any way to charge the load battery without going through the other battery.

I'd say that sooner or later you are going to have to switch to a complete 12V system. If you wanted to stay 6V all you needed to do was install a 6V alternator.

Marty

[grey beard]

Congratulations! You will do just fine with that setup. I've been recommending this very package for years. What many people do not understand is that polarity - positive or negative ground for any system - is limited to just the charging system and the battery. All other components - except for any solid state stuff you add later - do not care one iota about polairty, including the starter, itself. What you;'ve gone and done is made a system that has the best of both worlds, without destroying any originality that could not be put back later. JMHO

[Merle Coggins]

I've seen many, many cases of 24V systems (two 12V batteries in series) where an operator tapped off of one battery to run his radios (stereo and CB). Every case I've seen like this had a problem with short life on one battery. It was almost always the one that wasn't tapped for the radios.

As was said, the loads aren't equal on the batteries and the charging system will work to keep the more loaded battery charged up. This will tend to over charge the other battery, shortening it's life.

Your setup may work for some time without problem, but beware of shorter life of one battery.

Merle

[48mirage]

I believe with the low resistance of the Optima batteries the problem you identify will be diminshed some. As part of my routine maintenance I plan on rotating the battery positions. Right now I'm thinking once a year unless someone can offer me a failure curve that would suggest a faster rotation. I don't drive the car everyday, probably average twice a week to work 20 miles one way.