Re: Help Trying to Use D.C. Motor as Generator

On Wed, 3 Dec 2008 23:06:20 -0800 (PST), Techmann
<Inthemedia@xxxxxxxxx> wrote:

I have a D.C. motor that spins just fine when I apply 12V to it. The
motor has a 1/4" shaft and I would like to use it as a generator.
When I hook up a DC voltmeter to the leads and spin the shaft in the
same direction with my electric drill (around 1000 RPM) the most I
see out of the motor is only .24 volts. I am puzzled why I am not
seeing close to 12V output on this motor. Can only certain kinds of
DC motors be used as generators? Is it caused by the way the coils
are wired up internally and is there a way to test or change this so
that it can be made into a generator? Thank you.

T.C.

Yup only certain kinds. Some DC motors and all universal motors,
AC/DC (like your drill, vacuum cleaner, blender etc..) have field
windings to create a magnetic field. Some DC (only) motors use
permanent magnets to create the field - they make good generators
without modification. Some stepper motors make pretty good (if a
little small) AC generators.

A motor with a wound field can be made to work as a generator by
either exciting the field portion with a battery, or putting the field
in parallel with the armature so it is supplied by its own voltage.
(otherwise known as a parallel wound motor).

With that type of motor, used as a generator, the iron in the field
has to retain a little residual magnetism to start it producing power,
and it sometimes helps if it is not under an electrical load until it
starts producing current. A small permanent magnet can also be put on
part of the field to insure it starts (if the iron doesn't retain
enough magnetism - determined by the type of iron)
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