Re: Help with making SRSG phase control work?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Esondrmn@xxxxxxx 

Phil,

I am using an Oriental Motor purchased from C & H Sales.  Salient 
pole, 1,800 rpm, 1/25 H.P.  It has several wires coming from the 
motor, so you can reverse direction.  For discussion, let's say it 
just has three.  #1 and #2 to to the AC line and there is a 3.0 ufd 
400 volt capacitor connected from #2 to #3.

So you want to add a capacitor directly across the AC line terminals 
at the motor (#1 & #2 above) and use the variac, center terminal and 
one end as you described, in series with the AC line coming in.  You 
will need to do several tests, trial and error, to select the right 
capacitor.  It depends on your variac and the motor.  I am using a 
10A variac.  You want to see about a 5 volt resonant voltage rise on 
the input to the motor over the full range of the variac.  For my set 
up, the capacitor selection was very critical.  I ended up with 17.86 ufd.

My large coil uses a 1/2 H.P. motor and a 10 amp variac and 254 ufd 
of capacitance.

Good luck,

Ed Sonderman

In a message dated 1/23/2006 7:08:34 PM Pacific Standard Time, 
tesla@xxxxxxxxxx writes:
Original poster: FIFTYGUY@xxxxxxx

Folks-

     I'm not having much luck implementing a "Freau" style phase
controller for my SRSG.
     First, motor details:
     "Shinano Tokki" brand, P/N X7807-202V. 120V .35A, specs a 2.5uF
run cap. 1800 rpm. Exactly the same as the one shown in the pic:

<http://www.tb3.com/tesla/sparkgaps/1800srsg/P2210012.jpg>http://www.tb3.com/tesla/sparkgaps/1800srsg/P2210012.jpg

  which is on Terry Blake's prop gap site:

<http://www.tb3.com/tesla/sparkgaps/1800srsg/1800srsg.html>http://www.tb3.com/tesla/sparkgaps/1800srsg/1800srsg.html

     I've already constructed the entire SRSG, copying Terry Blake's
propeller style. I've also verified synchronism. I'm using a
stroboscope to check the phase control.
     Going by the schematic at John Freau's site:

<http://hometown.aol.com/futuret/page3.html>http://hometown.aol.com/futuret/page3.html

     The variac I've been using is a Staco model 291, 3A ~110V cute
little variac.
     Now, I started by simply inserting a variac in series with the
motor's line connection. I also added a 1-1/2 amp fuse in series with
the existing 2.5uF run cap.
     When I checked with the stroboscope, the most phase adjustment I
could get was perhaps 30 degrees. It acted weird, in that I could
adjust the variac to move the phase in one direction, but turning it
back to zero didn't move the phasing back with it. If I went more
than about halfway on the variac position, the motor dropped out of
synch. And yes, I'm only using the brush and one end of the winding,
so the variac is running like a variable inductor.
     Then I tried putting the variac in series with the run cap. This
had even less phase adjustment, and dropped out of synch even quicker.
     I used a clamp on amp meter, and neither of the motor windings
went over .4 amps under any condition.

     So back to the drawing board... I figured John meant I should be
adding not only a variac, but a new, larger cap in addition to my
existing run cap. In other words, the motor on his schematic really
represented the existing motor system, complete with its run cap.
     I took a 30uF run cap, and hooked up the circuit exactly as
shown on John's site. I kept the motor's own 2.5uF run cap hooked up normally.
     The motor ran fine at zero on the variac setting. As soon as I
moved the variac by about 10 degrees, I heard a buzz for about 5
seconds, then nothing. Motor kept running. Sure enough, the 1-1/2 amp
fuse had blown.
     I'm getting a little frustrated, and I don't want to burn
something up by blind trial and error. I figured if I'm having
problems with slightly smaller values of inductance and capacitance,
then I'm not going to attempt the experiment with a full 7.5A variac
and 47uF cap.
     Where does the motor's existing run cap fit into all of this?
     The motor has a run winding (125 ohms DC), and a winding in
series with the run cap (185 ohms DC). The ends of both windings are
connected to a common line lead coming out of the motor, so the motor
itself has only three leads. It's a nice little motor, so I'm not
going to attempt to run it without the run cap winding... Is there a
better way to test the phase change, without hooking the motor up?
I've got an o-scope.

Thanks!

-Phil LaBudde