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Re: Secondary size
To John C., Mike H., All;
Reading the two posts below, I notice that both talk about "radius to
winding length..." John, where you talk about Robert Golka's 1970's coil,
you mention that it was 50 feet diameter by 8 feet high. These dimensions
do yield a 6.25/1 ratio of diameter to height, but not of "radius to
winding length".
There have been a number of posts recently, more or less suggesting a
"standardized" language set, to describe various coil geometries, etc.
I would suggest that the term "coil diameter" and "coil height" be used
to describe a helical inductance's form factor, instead of "radius to
winding length." When I read "winding length," I think in terms of how
many feet of wire are being used. Certainly, it is correct to say that a
coil that has a large diameter, will also have a large curvature of radius.
You also mention below, that you modeled such a coil as Golka's or
Tesla's at 60 KW input. If you look at the design of my Model 13M
(www.ttr-dot-com,) you will find drawings at the end of the pages entitled,
"The Model 13M Story." Please note that the secondary of that system
utilized a 2/1 ratio of diameter to height. When energized at 100 to 125
KVa input, and loading into a 1/2 ratio diameter to height Extra coil,
there were frequent d'Arsonval type arcs (high current-moderate voltage)
between the transmission line and ground. These were approximately
7-8 feet long, in most cases.
I personally worked on Golka's "Project Tesla" when it was first set up in
the hangar at Wendover AFB, in 1977-79. Bob's secondary was 50 feet
in diameter, but it was actually about 10 feet high, and had about 26 turns
of # 4 AWG, spaced at about 3" between turns. The transmission line
between the top turn of the secondary and the input turn of the Extra coil
was almost 12 feet high above the concrete floor. This system also
exhibited frequent very high current arcs, from the transmission line, down
to the floor. The arcs were so intense, that where they connected to the
concrete floor, large chunks of concrete were literally "blown" out of the
floor, due to super heating and rapid expansion at the arc attachment
points. I observed the same characteristic from my Model 13M, however
in my case, the transmission line was above asphalt instead of concrete,
and the arc attachment locations made black colored spots in the
asphalt. The output of Golka's Extra coil had no "top load" in the form
of a toroid, or any other capacitive type device. However, it was being
operated inside of a virtual Faraday cage (the metal structure of the
hangar,) and may have seen capacitive loading from the building. I
personally placed a 6 foot long corona point on the top conical formed
top most turns of Golka's Extra coil, to try to direct the sparks. This
partially worked, as many of the arcs would go straight up and attach to
the apex of the metal ceiling. This was measured as a 52 foot straight line
distance. Still, even with this 6 foot long vertically placed corona point
on
top of the Extra coil, the discharges were so intense that many of them also
branched out horizontally, then downward to ground, or curling back around
in a semi-circular manner and attaching to various lower parts of the Extra
coil.
John, you may be interested in the measured data from my Model 13M
system. In this design, I employed a secondary that is 10 feet in diameter
and 5 feet high. The Extra coil itself, is 5 feet in diameter and 10 feet
high, (but elevated 7 feet high between the lowest part and ground.) With
125 KVa input, the best measured straight line spark length (not "controlled
sparks") was 55 feet. Drawings and some measured data are in the
figures at the end of the text on "The Model 13M Story."
Best Regards,
Bill Wysock
-------------------------------------------
Tesla Technology Research
----------
From: Tesla List
To: Tesla List
Subject: Re: Secondary size
Date: Tuesday, October 20, 1998 3:52PM
Original Poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
Mike -
You are correct in that the maximum inductance for the TC secondary coil
has a 10/9 ratio of radius to winding length with a fixed wire length. You
can find this inductance quickly with the JHCTES computer program. The
program will also indicate this ratio has two undesireable characteristics,
a high volts per turn and a short winding length that could cause
flashovers. With the program you can change the inputs to eliminate these
unwanted conditions.
You asked if anyone has built a coil with a high radius to winding length
ratio like Tesla's Colorado Springs coil. This was done by Robert Golka in
the 1970's. He told me he got 50 foot output sparks using 150 KW. I did not
ask him if these were controlled sparks!
The JHCTES does not cover such large coils, but as a test of the program
I show a JHCTES printout in the Tesla Coil Notebook of a coil this size but
using instead only 60 KW. The secondary coil is 50 feet in diameter by 8
feet high with a 6.25/1 ratio of radius to winding length. The program
showed a spark length of 37 feet. The numbers appear to be in the ballpark.
John Couture
----------------------------------
At 10:04 AM 10/17/98 -0600, you wrote:
>Original Poster: Hollmike-at-aol-dot-com
>
>In a message dated 10/16/98 5:49:53 AM Mountain Standard Time,
>tesla-at-pupman-dot-com writes:
>
>> Knowing this length you can design a
>> secondary coil that will give you the maximum inductance without
>> overloading the power transformer.
>John C.,
> Based on the Wheeler equation, the maximum inductance of a coil with a
>given length of wire occurs when the radius/winding length is 1.1111(or
10/9).
>That would produce a very short, fat coil that would not necessarily be the
>best geometry for a TC secondary. Tesla did use coils that were relatively
>short, with a large radius, but I believe he found it necessary to space
wind
>the coils to prevent excessive voltage stresses between the turns.
> Has anyone built a coil with such a geometry? If so, how did it work?
>MIke
>
>
>