Your description sounds similar to the AC output tachgen I've seen on some
small motors. They are using a (ceramic? ferrite?) magnetic rotor attached
to the motor shaft, with a coil wound on a bobbin. There are 2 steel disks
with fingers bent to surround the rotor (forming interlaced stator poles)
which are probably what's inducing the AC into the coil (my guess). These
are on Oriental Motor AC motors, where the output is 0 to about 100V for the
input into their variable speed modules.

I've also seen a little (synchronous, I suppose) AC gearmotor (approx. a 2"
cube) produced like this. It has two rotors and two coils on bobbins (2
leads per coil).
It's labeled Hurst Mfg Corp, Princeton Indiana (USA).
It's a 115VAC powered, and utilizes a 0.68uF capacitor when operated as a
motor. I haven't actually spun it with a meter attached to see what the
output would be (it's mounted on the back end of a motorized
variac/autotransformer).

WB
..................

"Mark Harriss" wrote in message
...

Thanks Oppie for the lead: I'm in Australia with a particular Wadkin
that the owner was later told was a prototype unit that should never
have left the UK let alone be sold to a client. The tacho is a multi-
phase ac unit with stationary windings and a rotating iron magnet and
no brushes. I'll have to get some part numbers next time I'm at the
machine.

Thanks
Mark




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