Should cut in by about 1000 rpm and stay charging at idle once it starts. If the light is coming on at idle and going off as you speed up and then coming on again at idle, you need to look at replacing the voltage regulator or just the brushes.
The rpm quoted for alternator 'load up point',(lamp out),..............
Is that engine rpm or alterantor rpm?
I would imagine that the actual rpm of the alternator is 2 to 3 times that of the engine due to the pulley diameter differences.
Not sure about that. I had a thought on the way to work that one of the easiest ways to build a small wind turbine would simply be to incorporate an old alternator. I've got lots of those around, but it seems that what I've found that the neccesary RPM's for alternators is too high to be the most practical.