Re: Rotary phase adjustment size question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 4/22/01 11:31:36 AM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

>  
>  Hi John, All, 
>  
>        I am in the process of constructing a SRSG with phase control using 
a 
>  1/7 HP motor, running in sync at 3600 RPM as verified by the modified RS 
>  Strobe light. The motor draws just under 2.4 Amps -at-120V. Since the motor 
is 
>  almost three times larger than in the example, I figure I'll need about 
>  120-150uF, 

Matt,

Some motors, especially if they use a run capacitor, will need much
less capacitance than expected.  Some actually can phase shift
with no capacitor at all.  It's possible that you'll only need 30uF
or so if it's a cap run motor.  But only trial and error testing will
tell.

> I have 48 15uf 660V run caps, so no problem adding capacitance. 
>  However, my available unfried variacs are 2.5A, 20A and 30A. Also have a 
10A 
> 
>  with a dark brown dead section 1.25" wide about 2/3 of the way along. 

If the dead section is shorted out turn-to-turn, it will need to be removed,
or the variac will draw excessive power.  The variac can be used then,
but will give less of a phase adjustment range most likely.  I suppose
any of the other variacs could be used.  The large ones are overkill
of course as you mentioned.  If it were me, I'd try using the small
2.5A one.  The variac does need to be able to handle the current,
but variacs can withstand considerably more than their rated current.
The fuse may need to be larger.  Sometimes the motor circuit
draws more current when the phase shifter is added.

Cheers,
John Freau


>  Matt D. 
>