SteveUnruh:
I agree with you about the fine voltage and current regulation of a Powered field.
But you can get the same thing with a charge controller that limits engine RPM.
A generator is a funny creature,
It does not know when to stop, thats why they added the current limiting section ( to protect it from itself trying to supply more amps than the windings can handle in an overload condition ).
An alternator is somewhat self limiting in current, but this comes at the price or a wider range in field current VS load requirements ( to overcome the synchronous reactance of the stator coils ).
There is also the rectifier section of the alternator that replaces the low voltage cut out on the generator regulator.
This is why Generator regulators are larger with 3 sections and Alternators have only 1 ( voltage control excluding the rectifier bridge )
In booth cases you need to put power into a field.
In both cases you have a narrow window where the magnetic core density and RPM are right for the most efficient conversion of mechanical power to electricity.
Once you are outside these windows small alternators and DC machines see their efficiency drop bellow 50%