Re: Testing - John Freau's SRSG Phase Controller

["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 12/19/00 11:43:17 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

Terry, all,

I'm glad the circuit is working well on your motors. I did some more
testing of the circuit, this time using a small 1/50 HP sync gap.  I first
tried using 25uF, but the voltage built up by 20 volts over the line voltage.
Next I tried 22uF, this gave a 10 volt rise, which is acceptable.  Then
I tried 19uF.  This gives no voltage rise at all, rather the voltage drops
by 3 volts at a certain position.  This arrangement causes the motor
to lose lock right at the end of the variac's range.  I still get the full
45 degree mechanical shift, and the 90 degree electrical shift.  These
degree phase shift figures are approximate.  I tried a 15uF cap, but
the voltage dropped too much, although I still got the full phase shift,
but the motor loses lock at 1/2 variac range.  It's an 1800 rpm motor,
which also uses a run cap normally.  I left the run cap in place of
course, and added the new phase shifter cap according to the new
circuit.  My other 1/20 HP motor which I did the original testing on, 
uses a start cap normally as part of motor.  So it seems that any type 
of salient pole motor works fine with this circuit, as would be expected.
Of course the cap size is critical, and should be selected to give
somewhere between no voltage rise, to perhaps a 10 volt rise.  It
might actually be good to aim for a 5 volt rise.  This would demand
a precise cap value.

> There is an auto transformer affect which tends to drive the variac's open
>  end terminal to high voltage (~200 volts AC) at the beginning of the range.
>   The high current across a small portion of the variac's winding causes
>  this high voltage at the other end.  Saturation and carful capacitor
>  selection controls this.
>  
>  The variac is probably not very critical but the capacitor's value is.  Too
>  low and the range is limited, too large and the currents and auto
>  transformer effects get bad.  I found that 110-130 is the range with 120uF
>  being the value you really want for a 60Hz, 1800RPM, 1/4HP sync motor.
>  
>  I did not see anything alarming except the conditions I mentioned above.
>  The thing seems very stable and nothing is getting overloaded.  It looks
>  like a real winner!!  The sharp current spikes of the motor do tend to
>  cause humming in the variac at certain settings but nothing bad is
>  happening.  I drew up the circuit I used at:
>  
>  http://hot-streamer-dot-com/TeslaCoils/Misc/SRSG14HP.gif
>  
>  Other motors will need the cap value adjusted but this should work for
>  60Hz, 1800RPM, 1/4HP sync motors.  Of course, all this is pretty new so
>  there may be hidden things we still don't know about.  However, it looks
>  great to me.
>  
>  Great idea John!  Your circuit will be around Tesla coiling for a very long
>  time!!
>  
>  Cheers,
>  
>   Terry
>