Re: Rotor size question

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

Original poster: FutureT-at-aol-dot-com 

Robert,

It's hard to say unless someone has tried such a rotor on that same
model of motor.  I think I heard somewhere that hystesis motors are
quite powerful for their size, but I'm not sure.  I use a 6.5" x 3/8" G-10
phenolic rotor on my 1/20 HP salient pole sync motor.  This motor seems
to be rather powerful for its size.

A large rotor is better for a number of reasons.  First it will give a
shorter mechanical dwell time for the electrode presentations.  This
is important because a too-long dwell time can cause the gap to
refire while the electrodes are still aligned.  If the gap refires, this
causes inefficient operation.  If you run more power, you need larger
electrodes, and this makes the refiring issue worse.  Second, since a larger
rotor gives a faster electrode closing speed, this results in less jitter
(I think).  Jitter is important because it determines just where the
gap fires along the sine wave peak.  The time of firing affects the
next capacitor charge, and jitter can cause instabilities and erratic
firing.  I saw this effect in a small NST powered system with a
small diameter rotor at 120 bps.  (At least I think this is what was
happening.)  Some of this jitter may occur because the spark
fires before the gaps are aligned.  The longer the electrodes linger
at a close spacing, the more "indecisive" the firing becomes.

John Freau


>I am wondering if my 1/20 hsp. cap-start motor will handle a 7" x 1/4"
>phenolic rotor or if I should use a smaller one- say 4 1/2" to 6". It is a
>synch hysteresis and I've noticed in searching the archives that some have
>had trouble when the rotor is proportionaly too large. Any help will be
>greatly appreciated- this thing needs to get built %^ )
>Why is a bigger rotor better? My next coil will be powered by two
><mailto:15000k-at-60ma>15000k-at-60ma NSTs.
>Thanks,
>Robert Hanford
>