Re: Ratio of primary outer dia.

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

Original poster: FutureT-at-aol-dot-com 

In a message dated 12/9/03 10:43:29 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

>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.


Dave,

A secondary is excited in a similar way regardless of the number
of turns in the primary.  Most of the energy goes into the bottom
section of the secondary either way.  Much analysis of this has
been done by Paul Nicholson and others.  These subjects has been
discussed a lot in the past and there's a lot about it in the
archives.

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.


If the secondary is stressed too much, it probably means the
coil is over-coupled or the bang size is too large.  Richard Quick
also advocated high break-rates.  It's the high break-rates that
permitted him to use the small capacitors and still get a large
enough power throughput, but with a smaller bang-size.  More
research is still needed on racing sparks however.


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.


If the capacitor and transformer is rated for the power, etc, it won't
fail.  Space-wound coils actually can give excellent results.  Large
capacitors can give excellent results also, if used with a low break-
rate.  Kevin Eldredge's Biggg Coil is a good example of this type
of design.  Kevin's coil should now be very efficient now that he
has replaced his old ballast which was heating and wasting power.
I forget what his latest efficiency results are unfortunately.
Kevin's coil is actually based on my recommendations for the
break-rate.

I like to use a large enough inductance in the primary
to give a rather high surge impedance which tends to reduce the
spark gap losses.  This often requires the use of quite a few
primary turns and also quite a few secondary turns to keep the
coil in tune.  Too many primary turns (and too many secondary
turns) is undesireable too because the wire losses will rise too
high.  A physically larger coil may be able to tolerate a lower
number of primary and secondary turns because the wide form
diameters tends to keep the inductance high anyway.


>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.


The flux field behaves similarly in either case.  Racing sparks
and secondary flashovers has more to do with coupling and
bang-size than with the primary size, shape, or number of turns.


>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.


See above.

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.


More recent research has found a number of flaws in such earlier
viewpoints.


>The large primary coil tunes with a much smaller (and cheaper) tank
>circuit capacitance which requires a smaller power supply to charge.


It is true that one of the advantages to using a high break-rate, small
capacitor and many-turn primary is that the capacitor can be cheaper.
The charging requirements should remain constant however for a constant
power throughput.


>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.


I have not seen any benefits from the above described design approach.
In my work, I've seen the best results using large capacitors, low
break-rates, and a large number of primary and secondary turns.
( high inductance really).   In any case, the difference tends to be
small for well designed coils.

As an added

>boon, the large primary coil and high inductance secondary form a
>"slow-wave" system.


I remember the Corums' mentioned something about slow-wave
coils.  I seem to forget what they were refering too.  They paid
a lot of attention to coil VSWR ratios but these do not in reality
seem to be very important for a sparking coil.  The Corums ignored
quite a few important factors in their analyses.

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.


It's true the peak bang size is lower, but the higher break-rates
advocated by Richard Quick may also abuse the caps depending
on their design.  The same goes for the gaps and power supplies.


The gaps quench easier and I have found

>that the tank circuit capacitors have a much longer life.


Again it depends on the design of the capacitors and their
rating.  I seem to remember that Richard Quick used Richard
Hull style rolled homemade caps.

I mention similar things to what I've mentioned above at my website
and there's a link to Paul's site also:

    <http://hometown.aol-dot-com/futuret/page3.html>http://hometown.aol-dot-com/futuret/page3.html

Well, we'll see what other folks have to say about the issue.

John
--


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
>
>
>