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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
> >