Re: Phase adjust

["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 12/24/00 7:45:25 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

> Hi Ed,
>  
>  I have a 1/4 Hp 1800rpm motor. With 50uF it would barely stay locked. With
>  100uF  I could vary the mechanical firing angle about 40 degrees. I think
>  even more capacitance would have been better in my case, but all I had were
>  two 50uF caps. I guess it's time to check out Surplus Sales!
>  
>  My $.02,
>  
>  Jon

Jon,

An 1800 rpm motor can never be varied more than 45 degrees
mechanical using this circuit.  45 degrees mechanical = 90 
degrees electrical for
an 1800 rpm motor.  For a 3600 rpm motor, 90 degrees mechanical
= 90 degrees electrical.  So you're just about at the limit now for
the phase shift capability for an 1800 rpm  motor.  If your motor 
is staying locked for only part of the variac range, then a larger
cap may help that.  I like to measure the voltage across the motor
with the cap in place, and look for about a 3 volt rise over the 
line voltage (max) at some point in the variac's range.  

Often, the circuit still works well with a smaller than full variac
range, and gives the full range.  Just be sure not too turn the
variac past that point during coil operation, to keep the motor
locked.

It will be good when we hear more reports from folks using
various sized motors, and what cap values they needed to
use.  I do have a 1/4HP modified induction sync motor, which
I have yet to try.  The bearings are shot and it makes a
horrific racket !

John Freau