Re: mini coil primary coupling ?

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "Laurence Davis by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
 >
 > I'm near to complete the mini coil.  I've decided to make a conical
 > primary, since i've heard they
 > are more efficient for a small coil.  I'm aiming for a coupling of 0.18,
 > which i thought I had heard was optimal.

Mode 5:6, with energy transfer in 3 cycles. A good mode, but quenching
starts to be a problem.

 > all other conditions fixed and
 > assuming a 'tuned' state, changing the primary spacing or
 > primary angle should only change the total output by about a 25% variance
 > (lets say coupling is a fixed variable as well).  Am i correct?

At this relatively high coupling, the system is quite insensitive
to small variations.

 > I've read
 > that there is a preferred ratio from primary width to secondary
 > height.  Why this relationship?  em field size of the primary compared to
 > the secondary?

Maybe just to be able to achieve the desired coupling, that is a
function of the geometry of the coils. 0.18 is not easy to achieve if
the secondary coil is long. For example, for the secondary coil
that I use in my experiments (32 x 8.8 cm) I would need a conical
coil with internal radius=7 cm, external radius=20 cm, and
height=8.5 cm to have k=0.18. No flat coil below the base of the
secondary would achieve 0.18, but a flat coil elevated a few cm would.
A conical coil is better in terms of insulation.
The low-frequency coupling can be set somewhat below the desired k,
because the nonuniform current in the secondary when in real operation
increases the effective coupling a bit.

Antonio Carlos M. de Queiroz