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Re: phase shifter with run-cap sync motors



Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-uswest-dot-net>" <mystuffs-at-orwell-dot-net>

john, all
in my testing of my 1/3 hp sync. motor i found that with the run cap of
12.5uf i
could not go over 20uf of phase shift capacitance or the spikes in the
waveforms
started to cause some sierious "bucking".
i tried different values up to 80uf where the motor simply wanted to jump
out of
it's cradel.
20uf seemed best for this motor giving a full 180degrees of electrical
shift from
the incoming waveform without to much resonant rise, the motor locked up at
65v if i
remembered right and held all the way through peak and back to 70 odd volt.
i was planing on getting some inductance readings of not only the variac
but the
motor windings them selves. it might be nice if we could get a little data base
going to layout a rough cap value for different run capped motors seeings
how they
require a somewhat different aproach? on motors that the run windings aren't
released at speed it is clear that the windings are definatly a part of the
overall
power factor corection of the phase adjuster cap to the inductor.
my rotor is two 1/2" lexan disks 10" dia. glued and screwed together.
more to come,
marc m.

Tesla list wrote:

> 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
> >