Todd,
The heat actually affects the rare earth magnets, a search on the internet should confirm this. I just can't remember the details. I guess the glue is another matter.
George (down under)
  Hi Ernest;
      From Georges comment, I gather that the heat sensitivity would likely be due to the glue that bonds the magnets to the inside of the rotor. This makes sense and also means that I shouldn't have much of an issue if no air blows under the rotor and onto the stator. Air movement around the rotor should be enough.
       I really am a lot less satisfied with "should" than I used to be.

  Todd
  C-FSTB

       
  On Sun, 2009-05-03 at 21:01 -0400, Ernest Christley wrote: Todd Bartrim wrote:
> I'm thinking about the cooling issue that you are addressing with fan > blades. How much heat do you think it will generate? I'm > thinking/hoping not much. I don't know about the original Harley > install, but as this is commonly used source of power, I got to > looking at my Ski-Doo, ATV and dirt bike. In everyone of them the > stator/rotor is completely sealed up and is not liquid or oil cooled. > And I've never had issues with them. It would be a simple matter for > me to put a small baffle at the exit of one of the evap cores that I > use for cooling and direct some of the air over the rotor, but due to > the tight fit, not much air would find it's way under to the stator.
I don't know what sort of heat load it'll generate, but it is almost immaterial to my installation.  For me, he intake air will be flowing over it regardless.  I've been told that PM alternators are only 50% efficient.  I find that hard to believe;  that would be a 500W heat source for a 40A generator.  But even at that worst case, it isn't an issue for me.