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AskTheRebuilder => Alternator Questions => Alternator FAQ => Topic started by: drew on September 20, 2010, 12:50:21 PM

Title: Isolated Dual Alternators For Motor-home Conversion
Post by: drew on September 20, 2010, 12:50:21 PM
Quote from: John P
I'm looking to convert a Step Van into a homemade motor home/camper.  Rather than REPLACING the stock alternator, I'm wondering about installing a second, high output alternator whose output would go only to the house batteries, thus avoiding isolator problems.  I'm wondering how to prevent the alternator from overcharging the house batteries on a long trip.  What would serve as the voltage regulator in a case like that?  Could the output somehow be wired through the same controller that controls charging when the motor home is plugged into shore power?  Could a magnetic clutch, such as is used on automotive AC compressors, be used to turn it off when it isn't needed?

John P

Excellent question John. Dual alternators are the way to go when dealing with battery banks you want separated. Battery isolators waste power, and all that power costs money, in gas or main-line electricity.

One caveat with dual alternators is the mounting. If you're using the Chevy P-30 Step-Van as your chassis, we offer a universal GM dual alternator bracket for vehicles '99 and up.

Dual Alternator Brackets: (

Now to control your alternator and keep it from overcharging your batteries, you need what's called a self-exciting voltage regulator, or SE voltage regulator for short. The self-exciting voltage regulator senses battery voltage and turns your alternator on as it goes below around 14.3 volts. There are several alternators that come optional with the SE regulator, but our most common and easy to deal with ones are the Si and CS series for GM; or the 3G and 6G series for Ford.

For dual deep cycle batteries, you need the most power and greatest durability, so I recommend the Extreme Duty CS144 Dual Rectifier Alternator: (