Re: Help with making SRSG phase control work?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 1/24/06 2:46:12 PM Eastern Standard Time, 
tesla@xxxxxxxxxx writes:


> Hi Phil:
>
> Are you certain your motor is a salient pole type?  Since you have a
> strobe, does the motor, without the phase controller, start up in the
> same phase position every time?
>
> I can't imagine why you blew the fuse.  The fuse should be in series
> with the 30 uF run cap that you added, not the existing 2.5uF run cap,
> but it still should not have blown.



Phil,

It's true that an extra cap should be added, but since you have a small
motor, you may need only about 3uF for this extra cap.  30uF may be
much too large and may be resonating the system too much thereby
blowing the fuse.  Not sure.  My schematic assumed that the motor
didn't have a run cap.  but it's fine to use motors that have run caps.

In any case after installing a 3uF cap or so in the way shown in the schematic,
then rotate the variac throughout its range.  At some point along the
range it's desireable to see a resonant rise on you meter of about
5 volts max above line voltage.  Measure the voltage across the motor
leads.  If you get 10 volts that's OK too.  If you get 1 volt, or no rise
that may be ok too, but the motor may lose sync-lock near the end
of the variac range.  You should get 45 degrees of mechanical phase
shift if it's an 1800 rpm motor  (90 degrees electrical phase shift).

John