A flyback diode isn't a diode that is especially made for use in a flyback situation; it's an ordinary diode that is used to prevent the voltage surge created by electromagnets when the electromagnets are turned off. The electromagnets are power output devices and a diode can only be used in a DC circuit, no AC.
Both generators and alternators are power input devices. A diode cannot be used with a generator or an alternator because either the diode is going to short out the generator or alternator, or the diode isn't going to do anything at all.
Douglas Krantz
