Re: stepper wiring and AC stepper

Hi,

It is an excersize if futility to use an "AC synchronous step motor"
as a bipolar step motor, though you can do it.

Just like "real" step motor, it has two windings except one end of
each winding is connected internally and the common wire is brought
out, for a total of 3 wires.

One winding ( common and one end) connects to 115VAC, driving it with
a 60Hz sine wave. The remaining wire has a capacitor in series that
provides a 90 degrees phase shift at 60Hz. This phase shift means
that winding is driven with a cosine current. Direction is determined
by which winding gets the cap.

What you have then is an infinite resolution microstepper that runs
at 240 full steps per second.

The problem is it is designed to run of off 115VAC at 240 full steps
per second. This means the motor must have enormous inductance to
limit current at such a low speed and high voltage.

This motor would require a 1,600 volt bipolar drive ( 10 times 115VAC
times 1.41 ) to get the same torque at 2,400 full steps per second!

You can open the back of the motor, identify the common connection,
seperate it into individual wires and bring them out. What you would
have after your efforts would be a motor that completely runs out of
steam at 60 full steps per second using a 40VDC driver. Not exactly
blazing performance.

These motors are cheap on the surplus market because they have near
zero value for anything other than its designed purpose; a fixed 72
RPM motor.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "Tom Eldredge" <harmonyt@r...> wrote:
> Marris,
>
> Ya know, I think you are correct. Now, how did I hook up those AC
> synchronous motors and drive them as biplar driven steppers?
Maybe they
> had three wires? I know they were AC because I used some as AC
motors.
> You could reverse them easily with a switch controlling the
cap/motor hook
> up.
>
> Tom Eldredge
> ----- Original Message -----
> From: <mariss92705@y...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Tuesday, April 03, 2001 12:04 PM
> Subject: [CAD_CAM_EDM_DRO] Re: stepper wiring
>
>
> > Hi,
> >
> > AC synchronous "steppers" do not have 6 wires.
> >
> > Mariss