Originally Posted by markopolo
I've been looking into High Output Alternators.
Does anyone know what the mpg impact would be if I went from a stock alternator to a something like a 200 amp, 120 amp at idle alternator?
I'm just trying to figure out real costs. I'd have to upgrade my isolator. Might have to upgrade some wiring.
My van has a 6.5l Turbo Diesel and from memory, it gets 17-18 mpg now.
If the MPG impact is too high then I'd probably not bother.
A high amp alternator may have slightly lower efficiency at lower outputs than a standard one, but I seriously doubt you would see it in fuel economy. You would need to upgrade any wiring and components that could possibly see the higher amperage.
Under normal conditions, the alternator is going to run at a set voltage, and the amperage will be determined by how much is being used. If you are going down the road with full batteries, no lights on, no accessories running, the amp draw will be very low, and the same as a lower maximum output alternator would be. The higher amps would only show up when needed.
As a point of reference, our Chevy 6.0 gas engine has a 145 amp alternator IIRC, which will do about 80 at idle. We have the 200 amp separator, and the wiring to the coach batteries is fused at 80 amps. To this point we haven't tripped the breaker.