Re: [TCML] Variable RSG

[FutureT@xxxxxxx]

In a message dated 4/9/2008 6:51:35 P.M. US Eastern Standard Time,  
quarkster@xxxxxxx writes:

>Let's also make sure that everyone is talking about the same type  of motor. 
When we're talking about a >motor for use with a Synchronous  Rotary Spark 
Gap, and "synchronizing" the rotor angular position >with the  sine wave of the 
AC power supply, we are usually talking about a "salient  pole" type motor, 
>either factory-made (like used in a Teletype machine) or  a modified (flats 
machined on rotor) >synchronous induction  motor.

>  Miles' original post dealt with  adjusting the phase of a "syncronous" 
motor, and there was no mention >of  salient-pole modification.

>  I've experimented  with John Freau's phase adjust circuit using 
salient-pole motors, and it works  as >advertised.

>  However, I've never tried it  on an un-modified synchronous motor 
(conventional squirrel-cage induction  >motor). Does it work on an regular 
squirrel-cage motor?

>  Regards,
>  Scott Hanson


Scott, all,
 
A conventional squirrel-cage induction motor is not a synchronous  motor.  
Such a motor
will always slip and run slower than the synch speed.  Such a  motor only 
becomes
synchronous when it's modified by grinding the flats.  Commercial  synch 
motors of
the salient pole types are sometimes called reaction synch  motors.  Still 
another
type of synch motor is the hysteresis synch motor.  This type will  lock into 
a
different phase position each time it's turned on.  It didn't seem  clear to 
me which type
of 2HP motor the poster was using.  I got the impression it may  have been a 
hysteresis
type since he said it locked into various phase positions.  But if  he has a 
regular
induction motor, then he'd need to grind flats onto it before it could  
possibly run
in synch fashion.  My phase shift circuit cannot work with a  un-modified 
regular induction motor.  It has to be modified first by  grinding flats.  
The key
will be what is written onto the name-plate of the motor.  If it  says 1725, 
or
3450 rpm, then it's an induction motor, not a synch motor.  A  synch motor 
will say 1800 rpm, or 3600 rpm (1500 rpm or 3000 rpm in countries 
using 50Hz AC power).   
 
I've never tried my phase shift circuit on a hysteresis type motor.   I think 
I
remember that someone said they tried it and it worked, but I'm not  sure.  
In any case since my circuit can only give 90 degrees of electrical phase  
shift, 
a few starts of a hysteresis motor may be needed before it can be 
brought successfully into phase using the circuit (assuming the  circuit
works at all with a hysteresis motor).
 
Cheers,
John









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