It also needs to be said that highest coupling is not the goal - more is
not necessarily better. Performance will generally increase with
increasing coupling, until an ill-defined threshold is reached. Increasing
coupling beyond that point will result in what's called "racing sparks" -
sparks across portions of the surface of the secondary coil that can
quickly destroy the secondary. You need to design the coil in such a way
that the distance between primary and secondary can be experimentally
adjusted to vary the coupling, typically by raising the secondary. For
most coils, using a flat spiral primary provides adequate coupling when the
plane of the primary is near the bottom end of the secondary.
Regards, Gary Lau
MA, USA
On Wed, Oct 14, 2020 at 4:26 PM jimlux <jimlux@xxxxxxxxxxxxx> wrote:
> On 10/14/20 11:10 AM, Douglas Johnson wrote:
> > What could one consider a good coupling starting point for a 3.5"
> > secondary? Even with the primary, maybe a little above or below?
> > Also, using tesla map, I see quite a difference in tuning by changing the
> > center hole size. Can someone explain this to me?
> >
>
> The coupling is determined by how much of the magnetic flux from one
> coil (the primary) is in common with the flux from the other coil (the
> secondary).
>
> A primary with a giant hole has lower flux in the center than a primary
> with a small hole - because the flux is distributed over a larger area.
>
> Consider a vertical solenoid primary - that will have the highest flux
> in the center, and is the highest coupling.
>
> I think someone (Greg Leyh?) built a coil with a solenoid primary
> *inside* the secondary.
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxxxxxx
> https://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla