Re: Tesla coil sizes and idea

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

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 

Tesla list wrote:
 >
 > Original poster: Dave Leddon <dave-at-leddon-dot-com>

 > This begs the question, what is the size and shape of the magnetic field
 > produced by a flat Archimedes spiral primary?  I've always assumed that it
 > was roughly spherical with a diameter slightly greater than the
 > primary.  If that assumption is true then wouldn't that argue for secondary
 > winding lengths not much greater than the diameter of the primary?

The magnetic field produced by any coil is just the sum of the magnetic
fields produced by the individual turns. The magnetic field doesn't
end at any particular distance. It just decreases in strenght with
distance. What matters is the coupling coefficient between the coils.
How the primary and secondary fields intercepts each other is not
important. Couplings in the usual range used in Tesla coils can be
obtained with primary coils of almost any shape. A flat coil is easier
to assemble than a conical coil. With a long secondary, it produces
weak coupling, but enough in most cases.
The Inca program can calculate coupling coefficients:
http://www.coe.ufrj.br/~acmq/programs

Antonio Carlos M. de Queiroz