On 28 Jun 2005 02:26:54 -0700, wrote:

Dear Jim,

wrote:
You've been wading in pretty deep water - although, at first
sight a self excited squirrel cage alternator sounds like a simple
device they're a positive feedback system. They're so touchy that
they're pretty well only used by dedicated amateurs - I don't know of
a single commercial application.

A positive feedback system would be unstable.

I do understand that the initial remnant magnetization is fed back to
produce more magentization, but since operation is on the capacitive
side of the Bode plot, I see negative feedback as the primary
characteristic.

That is, loading the generator incrementally produces reduced speed,
producing more output. This is negative feedback, stable
characteristic.

I would be very interested in hearing from you an explanation of which
aspects of the system are positive-feedback in nature, and which are
negative. Anyone else, also, is welcome to comment on this.

Doug


It is a positive feedback sytem and it is unstable. With a
sufficiently high loaded Q, feedback builds up the small residual
magnetic pattern in the rotor to produce ever increasing output.

This suicidal tendency is only controlled by both shaft available
input power (i.e. the speed drops) and the rising iron losses which
drop the loaded Q and modify the feedback phase angle.

Jim