Re: [CAD_CAM_EDM_DRO] Strange motor - question

Jerry Kimberlin wrote:

> I recently picked up a motor which was labeled as being made by
> Emerson. It was a 230vac, 60 hz, 3 ph, running at 3s50 rpm. Takes
> 3.3 A and had a K-2 on the label. Also listed at 1/x hp. The label
> is incomplete and I have no other information. There are 3 wires
> out.
>
> I tried running the motor using my Hitachi LJ100 VFD and got
> errors. The motor tried to turn but only got around about a third
> of the way. Eventually I opened up the motor and found it was 24
> poles which explained why the VFD didn't drive it.

How did you determine it was 24 poles? Did you just count stator
slots? Those are not the poles, but just slots to put coils into.

What is 3s50? Do you mean 3450 RPM? That would indicate
a 2 pole motor. But, even if it WAS a 24-pole motor, as long as it
was 230 V, 60 Hz, the VFD should run it fine.

>
> It is a nice small motor and appears to be 1/4 hp. The field coil
> and armature are about 3" long. There is nothing else inside the
> case, which is about 4" OD and 5 1/2" long, totally enclosed, and
> has a foot mount.
>
> I can't find out a thing on the Emerson/USMotor site so the motor
> must be an OEM/special. In fact I can't find much on motor
> construction so I don't know what 3 phase motors having 24 poles are
> used for.
>
> The question is: What have I got? Is this some sort of synchronous
> motor, or an AC servo? Anyone have any ideas - especially how I can
> run it off of a VFD?

If it has an ordinary squirrel cage rotor, that sounds like a standard
induction motor. An induction AC servo motor should run fine on
a VFD, assuming voltage and frequency are compatible. Frequency
and RPM would not be listed on the nameplate except as a maximum,
rather than a nominal operating condition. If the info you quote in
the beginning are from the nameplate, then it is an ordinary induction
motor.

Jon