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Re: A Question about SRSG

In a message dated 9/6/00 8:19:09 PM Pacific Daylight Time, tesla-at-pupman-dot-com 

>      I was wondering if an 1800 RPM 1/4 HP motor with four rotary 
>  would be considered synchronus? I don't know much about synchronism, and i'
> ve 
>  been having trouble accessing the archives (it keeps saying: Could not 
>  connect) so it would help if someone were to shed some light on what makes 
>  motor synchronus.


If the motor is truly exactly 1800 rpm, then it is indeed synchronous.
In a sync motor, the armature is "locked" to the rotating field of the
motor which will rotate at 1800 rpm in a motor with 4 poles.  In a
normal induction motor, the armature is permitted to "slip" some
which reduces the speed to below 1800 to about 1725 rpm, but 
it can deliver more torque this way while slipping.

In a sync motor, not only is the speed constant and locked to
the incoming AC, but the phase is locked also.  Phase means
time basically; a point on the motor rotor will always be at
the same spot relative to a certain spot on the incoming AC
sine wave.  When using a sync rotary gap, we must have a way
to alter the position of the spinning electrodes relative to the
fixed ones, to adjust the phase as needed.  This can be done
by rotating the motor in a cradle, by rotating the electrode 
assembly, or by shifting the rotor position on the motor shaft.
When the phase is adjusted correctly, the gap will fire at the
correct time so that max voltage is on the tank capacitor.
This position can be found by trial and error, or by calc, etc.
One way to find the approximate position is to run the gap
under fluorescent light so you can see where the spinning
electrodes are syncing with the incoming AC, then adjust
the phase so they are in the correct position relative to the
fixed electrodes.

The motor should be started up first, well before the coil.

John Freau

 Another thing (this might sound a little silly) is when do 
>  you turn on a motor relative to the power to the coil? I was thinking that 
>  you might be able to put a switch on the 120 VAC line and hook the motor 
>  it in parallel, so the motor started running the same time as the coil. 
>  if you did that, wouldn't the motor have to have some time to reach full 
>  speed? I've heard about positioning the rotor at angles (like 315 degrees 
>  something like that), and I think I know what this means, but i'm not 
>  sure... Any help would be very much appreciated.
>  Thanks,
>  - Joshua