Re: Small TC experiments

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

> "Ed Phillips <evp-at-pacbell-dot-net> wrote:
> 
> > ...If you keep the winding dimensions the same the inductance goes
> > up as the square of the number of turns, while the resistance only
> > goes up as the wire diameter.  Net result is that the Q stays the
> > same.

	This applies exactly to the ratio of the inductances of two coils of
the same dimensions, and also assumes that there is no insulation on the
wires to reduce the winding factors as the wire diameter goes down.  See
Grover [71], p 117 and others on following pages.  Of course, the
inductance of a long coil of variable length doesn't go up as N^2. 
There's the little factor of Nagaoka's constant, etc.  By the way, have
you seen the expression for a very accurate closed-form calculation of
Nagaoka which was in IEEE Proceedins a few years ago? 

> 
> The proportionality of inductance to turns-squared applies to a
> fully coupled winding, ie when all turns share the same flux, as in
> an iron cored toroidal winding for example. The opposite extreme is a
> coil in which air-cored turns are so separated that they contribute
> only their self-inductance, in which case L is proportional to turns.
> The tesla secondary is somewhere between these two extremes.


> Having said all this, for a disruptive coil, the secondary Q is
> of secondary importance. The potential advantage of increasing the
> inductance comes from the fact that for a given primary coupling
> factor, a larger primary inductance can be used, with possible
> consequent improvement of primary gap efficiency - a theory
> expounded by John Freau.
 
	Agree absolutely.  The Q goes to heck when the streamers form, as
evidenced by the decrement of the secondary voltage, so unloaded Q
doesn't mean much unless it is extremely low.

Ed