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Re: [TCML] Questions on the Freau SRSG Phase Controller
For testing the phase-shifting behavior, I've found the easiest thing is,
assuming you have a scope, tape a small magnet to the motor shaft. Place a
pickup coil (something with maybe a couple hundred turns) beside the magnet
and connect the coil leads to the scope input. Set the scope sync to "Line"
so the sweep is triggered by the mains phase. When the motor is running,
the pulse train generated by the magnet sweeping past the coil should shift
as you vary the phase-shift Variac.
Regards, Gary Lau
MA, USA
On Tue, Sep 21, 2010 at 8:03 PM, A Rothman <canihazpolepig@xxxxxxxxx> wrote:
> John,
>
> Yes, it's me, Aric. I've been off the list for a while, and out of
> coiling. I've decided to dust off some half-finished aspects of my old
> coil, and give it a go again. This includes the SRSG phase control, and a
> 4-MOT stack to replace a 15K/120mA NST supply.
>
> I wired-up a high-intensity white LED to a chain of Zener diodes, a
> rectifier diode, and a current limiting resistor, to illuminate the RSG
> rotor. The LED is illuminated for about 15% of each line cycle. Peak
> current through the LED is 150mA. I'm hoping it will suffice to allow me
> to
> view the phase-shifting behavior.
>
> Thank you for your help.
>
> Aric
>
> On Tue, Sep 21, 2010 at 4:22 PM, Futuret <futuret@xxxxxxx> wrote:
>
> > Aric?
> >
> > The setup may be OK as-is, if you're getting about 90 degrees of
> electrical
> > and mechanical phase shift before you lose sync lock as you keep turning
> > the variac. If you're getting sufficient phase shift, then you can just
> > put a
> > stopper on the variac so you can't accidentally turn the knob too far and
> > then use the system that way. Many folks have done that, and some of my
> > setups are
> > working that way. If you want to be able to obtain the full rotation of
> > the
> > variac, then you may need to add even more capacitance, but since you
> > say the thobbing threshold occurs sooner with more capacitance, then
> > perhaps more capacitance is *not* the answer. Usually it's possible
> > to obtain some resonant rise across the motor when enough capacitance
> > is used. It's not essential to have any resonant rise across the motor
> > however. Usually without resonant rise, the motor loses sync lock
> > (throbs) at some point as you rotate the variac knob, as you are
> > indeed seeing. The bottom line is that the main thing is that you're
> > obtaining enough phase shift. You can observe the mechanical
> > phase shift under ballast-type fluorescent lights although some folks
> > have trouble seeing the shifting pattern as you rotate the variac knob.
> > The phase shift effect is easier to see using a neon bulb strobe light.
> >
> > It's normal to see the voltage begin to decrease at some point along the
> > variac
> > knob's range. Usually a larger cap causes first a rise, then a decline
> > in voltage. With a smaller cap, only a decline may be seen. None of
> > it matters too much if you're getting enough phase shift, and provided
> > you don't rotate the variac knob too far and lose sync while the TC is
> > running.
> >
> > John
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: A Rothman <canihazpolepig@xxxxxxxxx>
> > To: tesla@xxxxxxxxxx
> > Sent: Tue, Sep 21, 2010 11:21 am
> > Subject: [TCML] Questions on the Freau SRSG Phase Controller
> >
> >
> > I have a SRSG, consisting of a 1/2 HP 3450 motor, modified for
> synchronous
> >
> > operation via the usual grinding of flats in the rotor. The motor is
> >
> > equipped with a second winding, in lieu of a run or start cap, to provide
> a
> >
> > second phase for starting purposes. It is switched out via a centripetal
> >
> > switch after the motor spins up.
> >
> >
> >
> > I have followed the standard schematic, but included a contactor which
> >
> > isolates the variac and the motor from the capacitor when power is
> >
> > withdrawn. I have increased the resonant capacitor value from 20uF to
> >
> > 105uF, in 5uF increments, and have not observed the resonant rise in
> > voltage
> >
> > across the motor terminals. What I do observe is a monotonic decrease in
> >
> > that voltage, as the variac is adjusted from minimum inductance upward,
> >
> > until the motor speed starts to fluctuate, accompanied by an even steeper
> >
> > drop in voltage, but with 5-10V oscillation in unison with the motor's
> >
> > throbbing. As I increase the capacitance, the threshold at which the
> >
> > motor's throbbing starts seems to come sooner in the variac's rotation.
> >
> >
> >
> > Help!
> >
> > _______________________________________________
> >
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> >
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> >
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> >
> >
> >
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