Andrew Howard said:
Does anyone know if its possible to use a motor as a generator (just an idea
I had). If you got something else to spin the motor directly, would voltage
appear at the motor's contacts?
I have no idea about any of this, I was just wondering about it.
ALL motors act as generators. This is actually part of the laws
of physics. If you could find a motor which didn't act as a
generator, then Lenz Law would be violated, energy would no longer
be conserved, and you could build a perpetual motion machine.
In normal use, motors consume less electrical energy when they
are doing less mechanical work... and this is a "generator"
effect. Spin a DC motor faster than it's normal speed, and it
will pump energy backwards into its power supply.
However, motors which lack permanent magnets won't act as generators
if you simply spin the shaft. "Field coil" motors need help to get
started. To make an "AC/DC" motor behave as a DC generator you have
to connect a battery temporarily to the motor while you force the
shaft to spin. This kicks it into operation, letting it power it's
own field coil, and then the battery can be removed. (If the shaft
should ever stop turning, the generator will need another "kick" when
you start cranking it again.)
AC induction motors are similar, they need a kick, but they also need
a device which temporarily stores energy for part of a cycle, and then
dumps some energy back into the motor coil for the rest of each AC
cycle. In other words, connect the right value of capacitor across
your induction motor and you've built yourself an AC generator:
http://www.qsl.net/ns8o/Induction_Generator.html
For hobby purposes, any small "permanent magnet" motor can be used
as a DC generator.
Try this: use some tape or a piece of wire insulation to connect
the shafts of two small motors together. Use a battery to run one
of the motors, then measure the voltage on the "generator". You can
use this generator to light a flashlight bulb or an LED... or to
run another motor.
Hobbyists who build their own Wind Power generators love treadmills
and other excercize machines. In particular, they love the large,
multi-horsepower DC permanent-magnet motors in these machines, since
they work great as high-amp DC generators, and the surplus catalogs
are full of them. (A similar DC generator, bought new, might cost
several hundred bucks!)
SCIPLUS: DC PM motor/generators
http://www.sciplus.com/category.cfm?subsection=18&category=174
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William J. Beaty SCIENCE HOBBYIST website
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Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
