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Re: [TCML] Variable RSG
In a message dated 4/9/2008 6:51:35 P.M. US Eastern Standard Time,
>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
> Scott Hanson
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
synchronous when it's modified by grinding the flats. Commercial synch
the salient pole types are sometimes called reaction synch motors. Still
type of synch motor is the hysteresis synch motor. This type will lock into
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
type since he said it locked into various phase positions. But if he has a
induction motor, then he'd need to grind flats onto it before it could
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.
will be what is written onto the name-plate of the motor. If it says 1725,
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
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
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).
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