Re: Secondary size

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

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

I'll give it a shot....


Subject: RE: Secondary size


 > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 > I would be ok with following a chart or just plain ol' going with what
 > the masses say they have used as sooo many do, IF there were some
 > reasons as to why they are in those ranges.  I may have to bite the
 > bullet and just go with what ever THEY say is right.  But even if it is
 > beyond my comprehension as far as the actual calculations etc.  someone
 > out there should be able to explain why you don't go over or under a
 > certain dia or hieght for a certain power input if you want good
 > results.
 >
 > Without going into the calculations one can explain why you want to
 > avoid a resonant size cap for an NST.  So why can no one offer solid
 > reasons for even one secondary dimension?

Height is essentially determined by output spark length (you're not going to
get 60" sparks from a 6" tall secondary...)
Height/Diameter ratio is optimally 4 or 5:1 (except for low power coils,
where tall skinny can work well, and for CW coils, as well)... I think that
this derives from a compromise between high inductance, coupling between
primary and secondary, and cost (it costs more to make a large diameter
coil)
# of turns is determined by desired inductance and tolerating resistive
losses.  1000 turns or so appears to be a good compromise.  Inductance, to a
first order, is proportional to number of turns squared, and high inductance
is good (since output voltage is roughly determined by the Ls/Lp ratio),
but, on the other, hand, lots of turns means lots of feet/meters of smaller
wire, which means more resistive losses.
Topload size is determined by several things:
a) desire to produce a decent electrostatic field distribution so it doesn't
spark over along the secondary
b) desire to have enough secondary C to store enough energy to support long
sparks
The primary C is usually chosen by the current available to charge it and
the time between discharges (break rate)
Everything hangs on the need to have the same resonant frequency for primary
and secondary.