Re: General Coil Design

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

Original poster: Paul Nicholson <paul-at-abelian.demon.co.uk> 

Ian McLean wrote:

 > ... 0.6mm copper and go for 1000-1200 turns on a 6 inch former
 > for a secondary length of 30-32 inches.  I have plugged these
 > figures into JavaTC and cannot for the life of me get the
 > results I am expecting.  The calculated resonant frequency is
 > below 100kHz, which can't be right.

It should be around 260kHz for the unloaded coil, for 1100 turns
over 31".   Perhaps you put 6" radius into JavaTC instead of
3" radius?   That would come out around 110kHz.

I don't know the answer to your questions about optimal
secondary design.  Around 1000-1500 turns is fashionable at the
moment, I think.  Others will have a better idea.

IMO the most important element is the topload, as this determines
the voltage at which breakout will occur, and how much charge
is available to support streamer formation.   I don't think your
post mentioned a topload.  Might be an idea to look and see what
toploads similar powered coils are using successfully.

The secondary is merely a secondary consideration, IMO, and should
be selected so that the chosen topload is charged up to a potential
comfortably above the topload's breakout voltage, but not vastly
higher.  That consideration will set the required secondary self-
capacitance (for a given bang energy and a guess at RF transfer
efficiency), and since you've already chosen a primary C value,
that then sets the ratio primary:secondary inductance.  The final
step would be to choose some secondary inductance that gave you
a reasonably practical primary coil, with not too high an Fres.

I should stress that this topload-first design approach is
probably not conventional, so I mention it just in the hope of
provoking discussion.

 > Sorry for the long email.

You've barely begun when it comes to long emails :) Welcome to
the list!
--
Paul Nicholson,
Manchester, UK
--