Re: Help with making SRSG phase control work?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 1/27/06 9:51:57 PM Eastern Standard Time, 
tesla@xxxxxxxxxx writes:



>      My theory is to just keep power cycling the motor until it
> "cooperates". :)


Phil,

As far as I know the only 1800 or 3600 rpm sync motors
that keep locking up in different phase positions are the
hysteresis types.  These motors
usually have the word "hysteresis" printed on them in my
experience.  If you take it apart, the armature is a smooth
metal hollow cylinder without any laminations or other
features.  I avoid the use of these motors for a sync rotary.
I don't know if "Oriental" has built any of these.

In contrast the armature of a sync
motor that always sync-locks in the same position will have
laminations and will not be hollow.  It will look more like
the armature of a typical induction motor.  There will be
2 or 4 areas on the armature that are different.  These
areas will either be ground lower, or covered with smooth
plates.  I've seen these in various sizes from the small
Oriental motors to larger 1/10HP motors.  These are the
salient pole types or similar types.  These are the types
I use for a sync rotary gap.  These motors are called
salient pole motors or reluctance sync motors. Of course an
induction motor can be modified for salient sync operation
as you have done successfully.  Some larger sync motors
over 1 HP may have separately excited field windings for
greater torque.

There is a third type of sync motor that is used in clocks
and timers.  This type has many little metal magnetic pole
pieces arranged in a circle.  These motors are usually very weak,
and run at a lower rpm.  I don't really know much about this
type.  They tend to look very different than motors we
would use for a sync rotary gap.  I would imagine this
type can start up in various phase positions that match
one of the many pole pieces.

In any case it's easy enough to just install some sort of
cardboard disc with a line drawn across it onto the motor
shaft.  Then power up the motor many times while observing
it under fluorescent light or using a strobe light, to see if it
locks up in sync in the same phase position every time.

There might be some other types of sync motors in the
size we might use for a sync rotary gap, that I am
not aware of.  I heard there have been improvements
is permanant magnet type sync motors.

John