phase shifter with run-cap sync motors

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

All,

The remote phase shifter circuit is used to remotely adjust the
sync gap phasing of a sync rotary gap, using the simple twirl of
a variac dial.  The phase shifter circuit can be seen at:

   http://hometown.aol-dot-com/futuret/page3.html

Alan Jones has made some valuable findings regarding the use of
the phase shifter circuit with run-cap sync motors.  Basically, for his
modified 1/8th HP motor, he needed no phase shift cap at all, just the
variac, and he obtained the full 90 degrees of electrical phase shift. 
(That's 45 degrees of mechanical phase shift because it's an 1800 
rpm motor).  His tests also suggest that the run capacitance, and
the phase shift capacitance can be traded against each other.  It
is unknown how other motors will behave.  Another interesting 
finding is that the total capacitance needed is much less than I
would have expected for that motor.  I pasted an e-mail from Alan
below, which includes a more complete battery of his tests, and
more complete comments and conclusions at the bottom.  I know 
from my own tests, that some run-cap motors do need the phase 
shift cap, but it is interesting and important to know that some do not.

John Freau
--
> >   Tests:  (specified run cap is 25uF)
>  >
>  >  small disc
>  >  25uF run cap - no phase cap - begin voltage = 122.2
>  >  max voltage = 135.9 - full phase adjustment 
>  >  reso rise 13.7v
>  >  
>  >  large disc
>  >  25uF run cap - no phase cap - begin voltage = 121.3
>  >  max voltage = 137.2 - in sync but slightly less than full phase adj. -
>  >  reso rise  15.9v 
>  >  
>  >  small disc
>  >  10uf run cap - 10uF phase cap - begin voltage = 121.5
>  >  max voltage = 121.3 - lockup position change
>  >  no resonant rise, slightly less .2v
>  >  
>  >  large disc
>  >  10uF run cap - 10uF phase cap - begin voltage = 120.7
>  >  max voltage = 118.7 - in sync but not full adjustment
>  >  no resonant rise, 2v less 
>  >  
>  >  small disc
>  >  5uF run cap - 10uF phase cap - begin voltage = 122.0
>  >  max voltage = 121 - loses sync easily
>  >  no reso rise, slightly less
>  >  
>  >  large disc
>  >  5uF run cap - 10uF phase cap - begin voltage = 120.5
>  >  max voltage = 119 no sync - no reso rise, 1-1/2v less
>  >  
>  >  
>  >  small disc
>  >  no run cap - 10uF phase cap - begin voltage = 121.9
>  >  max voltage = 120.2 - would barely hold sync
>  >  very little adj. - no reso rise, 1.7v less
>  >  
>  >  large disc
>  >  no run cap - 10uF phase cap - begin voltage = 121.1
>  >  max voltage = 118 no sync - no reso rise, 3.1v less
>  >  
>  >  
>  >  small disc
>  >  no run cap - 15uF phase cap - begin voltage = 122.5
>  >  max voltage = 120.9 - would hold sync but not easily
>  >  very little adj - no reso rise, 1.6v less
>  >  
>  >  large disc
>  >  no run cap - 15uF phase cap - begin voltage = 120.6
>  >  max voltage = 119.4 - no sync - no reso rise, 1.2v less
>  >  
>  >  
>  >  small disc
>  >  5uF run cap - 15uF phase cap - begin voltage = 122.5
>  >  max voltage = 121.7 - slight adj. possible - no reso rise, .8v less
>  >  
>  >  large disc
>  >  5uF run cap - 15uF phase cap - begin voltage = 120.3
>  >  max voltage = 119.8 - no sync - no reso rise, .5v less
>  >  
>  >  
>  >  small disc
>  >  10uF run cap - 15uF phase cap - begin voltage = 123.1
>  >  max voltage = 137.2 - reso rise 14.1v - some adj. possible
>  >  
>  >  large disc
>  >  10uF run cap - 15uF phase cap - begin voltage = 120.8
>  >  max voltage = 132.5 -  reso rise 11.7v - no full adj. of phase 
>  >  
>  >  There was more resonant rise with the 10uF run cap and 15uF phase cap
>  >  (14.1v) than with the 25uF run cap and no phase cap (13.7v) using the
>  >  small rotor. But with the large rotor in place with the 25uF run cap
>  >  and no phase cap the resonant rise was 15.9v, where in the last test
>  >  above it was only 11.7v rise. The test with the large rotor
>  >  experienced more reso rise in the normal running mode that I would use
>  >  with the small rotor. The results seemed to swap where the 10uf-15uf
>  >  small rotor was higher and the 25uF-0uF large rotor was higher.
>  
>  Yes, those are the two sets of tests that I focused on also.  They
>  seem to show that the degree of loading (disk size and weight)
>  affects things to some degree.  That aspect is hard to interpret,
>  but may be related to a changing of the power factor with different
>  loads or something similar.  To me, there are four very signicant
>  findings.  First, that a resonant rise can occur with a run-cap only 
>  (no phase cap).  Second, that a motor can lock throughout the
>  variac's range with no phase cap at all, just a run-cap.  Third, is that
>  the value of one cap can be directly traded for the other, at least 
>  within some range of uF values.  I did not think this was possible
>  when you had suggested it, but it turns out you were right.  Forth, 
>  the combined uF value of both caps (run-cap + phase cap) is less
>  than I would have expected for the size of the motor (1/8th HP).
>  Marc M also said he was seeing unusual behaviour also with a run-cap
>  motor, and needed a smaller than expected phase cap I think.  
>  I did do a test of a small run cap motor, but I missed this effect,
>  possibly because my run-cap was so small at only 3uF or so.
>  Also this was a commercial sync motor, instead of a modified
>  motor such as yours and Marc's.
>  
>  So the bottom line is that a run cap motor may need a much
>  smaller phase shift cap than expected, or even none at all, as
>  you've been saying all along.
>
>  John
>  
>  >  
>  >  Alan
>