On Tue, 8 Mar 2011 23:31:31 -0500, "Josepi"
wrote:

Your friend was wrong. Motors need a magnetic field, whether permanent
magnet or electromagnet to produce voltage.

Three phase motors are typically induction types and produce the second
field of magnetism by induction from the wound fields.
Dynamic braking can use the collapsing field while they are turning for a
only short time to generate power but then the field is gone.

--------------------

"Existential Angst" wrote in message
...

Awl --

So I'm amassing a collection of perm. mag. DC motors for my various
(de)generative follies, but a friend said he took apart a gas powered
generator, and observed no magnets, with both stator and rotor being
wound -- suggesting that AC induction motors should provide juice, but mine
don't.

Was my friend wrong, or can wound rotors/stators yield juice, and if so,
under what conditions?

Many of the smallish generators (5KW to 50KW) in the Army had wound
rotors. They worked by bootstrapping: remnant magnetism in the iron
generated a small field current, which increased the generated
voltage, increasing the field current.... until the output voltage or
field current reached a threshold where some means of regulation
engaged. Occasionally a generator would fail to generate because
there wasn't enough remnant magnetism to get it going. The solution
was to "pole" the field by applying DC to it to re-magnetize it.


How are back-up generators generally wound, as well as prime generators,
such as coal, hydro, etc?

Will a typical 3 ph motor throw out juice, if driven by a pony motor?

In a way. It must be excited by the proper 3phase AC voltage, but if
the pony motor then spins the 3phase motor above synchronous speed,
the direction of current flow will be such as to deliver power to the
power line. An electric meter on that line would run backwards.