Sounds like an induction motor.  If you just spin it you will get squat.  As
a motor it has a rated speed at the rated hp.  Unloaded it will spin a
little faster.  There is a theoretical synchronous speed that the motor
would spin if there was no friction.  As you load the motor it slows by a
slip speed that grows as the extracted power increases.

To use it as a generator you connect it to power and spin it FASTER than
synchronous speed.  This gives a negative slip speed and produces negative
current load (generation!).  This means you have to have a power source
available to get things started, and you need good speed regulation of your
power source.

Doug Butler
Sherpa Engineering


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Gary Neal
> Sent: Saturday, November 23, 2002 7:59 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [EE]:3 phase motor as a generator?
>
>
> Guys,
>
>         I've got an old 3-phase 230/460V, 3/4hp electric motor
> that I was thinking
> about using for a generator (maybe as part of a windmill).
>
> Here's all the details I know:
>
> 9 lead wires
> Seems to be a wye configuration
> When spinning the shaft at 900rpm, get ~10V line-line on the outputs
> The Rotor has no wire connections or slip rings or anything.  Just a bunch
> of laminated plates that spin on bearings (not magnetic)
> Rated speed is something like 1170rpm
> Really very basic motor
>
> So, I've got a couple questions:
>
> 1.      What "type" of motor is this?  It's sad to say, but I
> went through an
> entire Mechanical Engineering curriculum, and they taught us all about the
> "theory" of electric motors, but never taught us how to identify the darn
> things.  Is it induction, synchronous, ...?  How does it work?
>
> 2.      If I end up using it in a windmill, I'd like to run it at
> low speeds
> (couple hundred rpm) and charge a 12V battery.  Is there an easy
> way to get
> higher V/rpm?
>
> 3.      I've seen discussions about needing to have "running"
> capacitors or be
> hooked to the grid and then spin the motor slightly faster than its rated
> speed to generate electricity.  This was all over my head and I
> was getting
> disappointed until I just took a couple LEDs and hooked them across the
> leads, spun the shaft, taaadaaaa, they lit up = electricity out.  So,
> what's the deal with that?
>
> Thanks,
>
> Gary
>
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