Re: A new idea? ...different geometries in coil construction more efficient?

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

Original poster: "Mr Gregory Peters by way of Terry Fritz <twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>

The ultimate source of voltage rise in a tesla coil is resonant rise.
However, it is unavoidable that some parasitic conventional turns ratio
transformation will take place. This is "all bad" as it interferes with
the free resonating of the coil and therefore reduces output and can aid
in coil failure.

Primary shape determines the maximum coupling possible. The coupling for
a "Conventional" two coil tesla coils needs to be fairly low (0.05-0.3,
depending on size and construction of coil). Any higher coupling will
result in the point of critical coupling being exceeded, whereby the
source of voltage rise in the coil will become dominated by transformer
action rather than resonant rise (much less effective), and power input
will be greatly restricted as the coil "burns up". The flatter coils
such as pancake and cone primaries will generally easily achieve these
low coupling levels if properly constructed. It therefore makes sense to
use these forms, as they are less prone to strikes, and although they
can't couple as well as some other shapes, they provide enough coupling
for most purposes. 

It is only in magnifier systems, where the secondary is intentionally
used mostly as a conventional transformer, that tighter coupling is
required for maximum power transfer. In these systems, the highest
possible coupling is desired and a traditional cylindrical shape primary
is used. Magnifiers really begin to perform at coupling levels over 0.4. 

In summary, I wouldn't bother too much trying to increase the coupling
of your coil.


Cheers,

Greg Peters
Department of Earth Sciences,
University of Queensland, Australia
Phone: 0402 841 677
http://www.geocities-dot-com/gregjpeters