Old post regaring synchronous motors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Daniel McCauley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

Here is an excerpt from the archives regarding various types of synchronous
motors (as we've been discussing in the latest synch motor thread)  The
original excerpt was by John Freau December 2000



>>>>>>>>>>
There are basically 3 types of sync motors for sync rotary gaps;
Hysteresis, Salient pole, and home modified induction motors.

Avoid the hysteresis motors like the ebola virus!!  They are NG for
our use.  I had tested one in the past, and I thought it locked
in the same position all the time, but I retested it, and it does not.
Fortunately, these motors usually are marked as hysteresis types.
The armature is a special metal that has a large hysteresis
characteristic, and so it can lock in any random position.  If you
use this type of motor, you'll have to re-adjust the sync phase
every time you run the coil... not fun at all.  I wonder if grinding
flats on these motors would make them lock in the same position,
I wonder if anyone has tried that?  Somehow I suspect it won't
work well.  My hysteresis motor required the use of an 8uF capacitor,
and I was surprised that it worked poorly with a 15uF cap, I don't
know if the cap size is critical on all hysteresis sync motors.

The salient pole type is what we want.  These motors often don't
even say sync on them.  The clue is the rpm of 1800 or 3600, or
1500 or 3000 for 50Hz locations of the world.

Lastly are the modified induction motors.  Just take any 1725 or
1750, or 3450 rpm induction motor from a washing machine, clothes
dryer, etc, and file, grind, or machine flats on the armature, and this
will make the motor synchronous.  1725 gets 4 flats about 1/3 the
dia of the armature, 3450 gets 2 flats about 1/2 the diameter of the
armature.  The width of the flats is not real critical but should be the
same for balance.  You'll lose some power when it's modified, and
the motor will run hotter.  But many folks have used this method
and it works perfectly.  There's a method of using the dead poles
to decide the width of the flats, but many small motors don't have
dead poles, so I just ignore this dead pole method.  The 1725 rpm
motor will jump up to 1800 when it's modified, and the 3450 motor
will jump up to 3600 rpm.