Re: Ratio of primary outer dia.

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

Original poster: Dave Leddon <dave-at-leddon-dot-com> 

At 11:22 AM 12/8/03 -0700, you wrote:
>Original poster: Esondrmn-at-aol-dot-com
>In a message dated 12/7/03 3:46:24 PM Pacific Standard Time, 
>tesla-at-pupman-dot-com writes:
>
>
>>Hello,
>>
>>Does someone have a rule of thumb for determining  primary outer diameter
>>based on secondary diameter and height?
>>I did an archives search, but came up with nothing definitive.  I am sure
>>that there is a ratio for optimum performance.  Also, if John Couture is
>>reading this, are you planning on publishing an updated version of your
>>construction guide?  Mine is from the early 90's, and I was curious if you
>>are planning to integrate some of the last decade's developments into a new
>>book.  I certainly hope so.
>>
>>Thanks,
>>John Richardson
>
>
>John,
>
>On my coils, which use flat primaries, the outer diameter of the primary 
>just ends beigh what it is by default.  Depending on the secondary size 
>and input power, I decide what I want for the I.D. of the primary, tubing 
>size and spacing.  I always wind the primary for 12 to 14 turns.  I prefer 
>to run my coils with at least 10 turns used on the primary to keep the 
>surge impedence lower to make it easier on the caps.  The primary on my 6" 
>coil is about 26" in diameter with about 2.5" inside clearance.  My 3" 
>coil primary is about 16" with about 1.5" inside clearance.
>
>Ed Sonderman

Hi Ed,

Sounds like you're an adherent of the Richard Quick school of primary design.
Time to introduce some controversy.


While Dr. R advocates:

If you are in the range of 6-12 turns (with NST) or 3-8 turns (with pole
xmfr), you have a good, but not optimum capacitance.

Now, we tune for optimum capacitance by adding more capacitors and reducing
the # of primary turns.  Our final goal is 6-12 turns with NST or 3-6 turns
with pole xmfr.  A large capacitance value provides more peak current and
additional energy available to couple into the secondary system.

This "turns reduction" as I call it usually provides significant improvement
in secondary output (assuming your spark gap is up to proper quenching of
additional current).

But Richard Quick has the opposite philosophy as quoted from the archives:

The small five turn primary at the base of a coil does a very poor
job of uniformly exciting the secondary coil. Most of the energy
is forced into the bottom third of the secondary winding on these
systems and these turns are unnecessarily stressed. The solution
was frequently to space wind to unstress the secondary, which in
turn reduced the ratio of turns transformation, which further
crippled the poor design. The small primary, large capacitor, space
wound secondary is a design loser. These systems are highly stressed,
inefficient, and require large and expensive capacitors and trans-
formers that are prone to high failure rates.

The solution of course is to move in the opposite direction. The
primary needs more turns which cover a larger area. This means a
substantially larger primary coil. Instead of a five turn primary
coil tapped in at three turns, the coil needs to have fifteen turns
tapped out at twelve or more turns. This primary design creates
a much larger field flux which completely engulfs the secondary
winding. The resulting excitation is much more uniform.

What happens next is very interesting. Because the secondary coil
is uniformly excited, the secondary coil can be close wound with
magnet wire without breakdowns and excessive corona losses. The
close wound magnet wire secondary has a very high inductance per
unit volume of coil form. When coupled to a large, high inductance
primary, the resulting coil set will achieve the same ratio of turns
transformation as the small primary design discussed previously.
This is a "win-win" situation.

The large primary coil tunes with a much smaller (and cheaper) tank
circuit capacitance which requires a smaller power supply to charge.
Yet the system is able to process power more efficiently because of
the large field flux and uniform excitation of the high inductance
secondary. The overall RF power processing efficiency is so great
that coilers who follow this design method blow away other designs
by producing bigger sparks with much less input power. As an added
boon, the large primary coil and high inductance secondary form a
"slow-wave" system. The tank circuit operates at a lower frequency
with less peak power which in turn reduces the stress on the gaps,
caps, and power supplies. The gaps quench easier and I have found
that the tank circuit capacitors have a much longer life. Run times
are longer with a higher duty cycle. When something finally does
fail, it is cheaper to replace.

So who's right?

My personal experience with a 12" diameter pig fed coil supports Richard's
observations but I see pictures of a lot of large coils using primaries like
those described by Dr. Resonance.  So, what's the consensus among those of you
who have built pig-powered coils?

Dave