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

[Futuret <futuret@xxxxxxx>]

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withdrawn.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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