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Efficiency of various coil form designs (fwd)



---------- Forwarded message ----------
Date: Mon, 18 Jun 2007 00:58:00 +0000
From: Jeff Behary <jeff_behary@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Efficiency of various coil form designs

Hello all,

This is "round two" of my ramblings :) ...

I agree with Bill Wysock 110% on the various forms of coil forms and their 
attributes.  I'd like to add a few comments on that subject.

The efficiency of any form of Tesla Coil depends on the application and use 
of the coil also, and this hasn't been mentioned.  Of course, maximum spark 
length would imply resonance, and for most modern coilers that is a good 
indication of performance.  But for specific applications using Tesla Coils, 
the "qualities" of the discharge is sometimes more important.

Starting in the teens companies such as H. G. Fischer, Campbell Electric, 
Frank S. Betz, Remco, Sterling Laboratories, McIntosh Electric Corp., Master 
Electric, Haliwell-Shelton, Shelton Laboratories, Rogers Laboratories, 
Bleadon Dun, Chicago Scientific, Energex Co, Challanger, Violet Ray 
Corporation, Browne Electrical Laboratories, LE Knott Apparatus Company, 
Cenco, Renulife, Eastern Laboratories, Master Appliance, Gibbs Brothers, 
Sheidel-Western, Amos Cato, Contra-Pole, Wappler, Waite & Bartlett, 
Machlett, Elco-Lindstrom, Fitzgerald, Parco, Re'juvin Laboratories, Tuckers 
Mfg. Co., Viracorp, A. S. Aloe, Ajax, Electro-Technic Products, Fromm 
Industries, and many other smaller companies in the US made small Pancake 
Coils for therapeutic use known as "Violet Rays".  These machines were made 
to produce a spark about 1" long consuming from 15 - 30 watts of power.
A requisite of the spark was to create local heat through special geissler 
tube that conducted the current to the skin.

The measure of the efficiency of these machines was not spark length but 
rather the nature of the spark.  It must have been able to "fulgerate" (a 
form of spark cautery) the skin at short spark lengths (1/8- 1/4"), heat 
below the skin to a noticeable degree when in direct contact with the body, 
and dehydrate the skin when sparking 1/2" or more from the surface.  A 
further embodiment of some of these machines was the ability to power a 
small X-Ray tube for treating skin disorders.  (Dangerous I know, but its 
history).

At first sight these machines may seem like old rubbish, but I would pose a 
challange for someone to try and make a helix coil that still fulfills these 
needs and can be made 1" diameter and 3" tall (Primary and secondary coils 
included).  It isn't impossible - a very fine wire secondary of small 
diameter can be made to create a 1" spark, but often the output is too 
feeble to be used in the above manners.  Of the hundred or so machines of 
this variety that I have owned, all of them used
Pancake Coils.  They were all sightly different in design from model to 
model.

Second, as far as "visible" efficiency goes, these same small coils can 
produce sparks 2 - 4" long when the input power increased to 75 - 100W.  
(For those familiar with the circuits, adding an extra magnet coil or two in 
parallel will do this) The small Pancake coil must be thrown in oil to avoid 
spark-overs, but this is also pretty good for a 1" x 3" coil, P & S 
included.

Sorry in advance for the crude setup, but I have some photos of that:
http://www.electrotherapymuseum.com/2006/VROil/index.htm

Next application is Tesla X-Ray Coils.  This is an application that is 100% 
possible to use today for portable X-Ray machines, even with the modern 
Coolide tubes.  My Kilowatt twin Pancake Unit
can demonstrate some fierce RF flames 7-8" long that could be enclosed in 
the normal housing with oil and an X-Ray tube (lead lined of course).
http://www.electrotherapymuseum.com/2007/HighResCoils/KilowattKinraideFlames.htm

[An interesting note as to how to control the filament voltage - another 
Tesla concept 100% - impedance - a loose coupled coil wound on the outside 
of the primary can be used to power the
filament of the tube by impedance - controlled by a rheostat in the same way 
as a filament transformer.  
http://www.electrotherapymuseum.com/2006/Figure1/images/Fig1-04.jpg    ]

This is an application where cylindrical Tesla Coils have almost always 
failed, with exception of two oil-filled versions made by LE Knott Apparatus 
Co. and Elihu Thompson:
http://www.electrotherapymuseum.com/Library/LEKnottApparatus/index.htm
http://www.electrotherapymuseum.com/2007/ElihuThomson1/pages/ff0596.htm

In these two coils the Primaries extended the whole lengths of the 
secondaries to allow very close coupling such as the coil in this article:
http://www.electrotherapymuseum.com/TeslaArchive/ATeslaCoil/index.htm

Even some Pancake Coils for this purpose failed.   While nearly all Tesla 
Coils can produce X-Rays with a proper tube, the qualities of the discharges 
greatly effect the ability of the X-Rays to make proper radiographs.  Its 
the qualities of the discharge and style of X-Ray tube that determines 
whether your X-Ray plate will show a pretty picture of bones or a blurry 
mess.

The same style coil when powered by a tank circuit to produce long sparks 
may produce discharges 12 - 16" in length or more.  Despite the increase in 
spark length, the discharges are still hot in nature.  The heat can be felt 
several feet away, and if the spark touches your skin you are in for a 
painful surprise (bad RF burn):
http://www.electrotherapymuseum.com/Forgotten_Tesla_Technologies/Early_Prague-Coil_Testing/index.htm

One of the few areas of the past where helix coils were preferred was for 
surgical Tesla Coils.  A thick wire secondary (18 AWG) on a small coil form 
(2" diameter x 4" long) with a 1/4 or 1/2 KW power can produce up to a hot 
1" spark all day long for cooking and cutting tissues.  It sounds horrid, 
but many lives were saved this way.  In the case of malignant tissues, the 
cooked tissues/cysts/etc. could be safely removed without reinfecting other 
parts of the body with infected blood.  There was little bleeding involved, 
and recovery time was much sooner and with a greater success rate than the 
scalpel.


Aside from medical apparatus, early Tesla coils were used commercially in 
wireless telegraphy devices as well, but I don't have much experience in 
that arena to comment on the nature of the sparks produced for this.  I have 
attempted though to make some color renderings of the coils Tesla
created for this purpose.  Most had mercury interrupters.
http://www.electrotherapymuseum.com/TeslaArchive/Construction.htm

Jeff Behary, c/o
The Turn Of The Century Electrotherapy Museum
http://www.electrotherapymuseum.com

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