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Re: [TCML] Questions on the Freau SRSG Phase Controller
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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