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RE: oudin coil (fwd)

---------- Forwarded message ----------
Date: Sun, 01 Jul 2007 04:28:28 +0000
From: Jeff Behary <jeff_behary@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: RE: oudin coil (fwd)

Hi Scott,

That's a simple and reasonable question with a lot of complex and illogical 
history behind it.

The original apparatus was called an "Oudin Resonator".
In the early days, Tesla was developing his coils in the US and in France a 
man named Arsene d'Arsonval was developing the same thing only without a 
secondary coil.  d'Arsonval was taking the output from either end of the 
primary coil and using it to cause heat in the body.  This was later called 
Diathermy, Thermo-Faradism, Thermo-Penetration, and a host of other terms 
depending on whether it was used for therapy or destructive effects 

Both Tesla and d'Arsonval were given credit in medical books for discovering 
high frequency currents.  Tesla didn't like this, and went to France to sort 
it out personally!  After he got there and met him, and saw the apparatus 
that d'Arsonval developed, it was said that he enjoyed the visit so much he 
decided to drop the issue of priority completely.

A friend of Arsene named Paul Oudin found out that if you connect a coil of 
longer finer wire to this "d'Arsonval" coil, you could get a higher voltage 
from it.  In the original apparatus there was no coupling of the coils, in 
fact the primary coil was wound horizontally on a table and the secondary 
was simply placed next to it (vertically) and connected to one end!


Oudin later found that if this coil was placed inside of the other or in the 
same field that the efficiency was greatly increased.  Many early designs 
were a coil form where the primary was wound on the bottom and the secondary 
wound on top, and still others had a single layer of space wound wire with 
the bottom portion of this used as the primary coil.

The original construction used a 12-24" induction coil for the power supply. 
  The spark dischargers of the induction coil were used as a spark gap, with 
the rods set an inch or so apart.  Two Leyden jars were placed in series 
with this gap and the "Oudin" resonator.  It was a simple Tesla Coil 
circuit, but the proportions were different.  Most Oudin Resonators were of 
large diameter and thick wire.  Perhaps 10" - 12" in diameter and 3 foot 
tall, wound with 1mm wire spaced a few mm apart like a giant spring.


The electrical output of these was normally a strong (and slightly painful) 
spark 2-3" long, yet a soft corona discharge ("effluve") 12" long.  A 
"patient" was connected to a ground plate and a needle electrode (or disc of 
needles) was approached about a foot away from them.  Between them and the 
discharger a corona effect would occur and the whole of the air would ionise 
between the electrode and the person's skin.  The physiological properties 
of this are numerous and can be found in early books.  Tesla said it was 
like being bombarded by miniature hailstorms, and though it sounds strange 
he was exactly correct with that analogy.  Its a bit like getting shrunk and 
placed inside of a plasma ball, then having it switched on...


Companies like Scheidel Western made huge outfits and even bipolar coils 
specificially to use these ionising effects.

As time progressed (around 1920) the "Oudin Resonators" began to look a lot 
like the modern Tesla Coil.


(from 1890s-1910 most "Tesla Coils" marketed were Pancake Coils).

As time progressed to the 20s and coils more or less all began to look very 
similar, another definition that appeared specified that Tesla Coils were 
bipolar coils (a horizontally mounted cylindrical secondary coil unearthed, 
floating in a primary coil) and Oudin Resonators were "grounded" and 
"uni-polar" - the ground typically being a connection to the primary coil 
with the bottom turn of the secondary.  By the mid 20s, Oudin coils were any 
coil that had a common connection between the P & S coils, and a Tesla Coil 
was a grounded coil that wasn't in any way connected to the primary coil.

The definitions overlapped and were as confusing then as they are now.  
Tesla's original patents showed Pancake, Conical, and cylindrical coils all 
that were grounded.

To add to the confusion with priority issues of Tesla and Thomson, some 
books referred to "Oudin Resonators" as one class and "Tesla-Thomson Coils" 
as another class, with "d'Arsonval" coils being a third class without a 
secondary coil.

To add even more confusion to the historical definitions, voltage outputs 
were also used to determine the names given.  d'Arsonval currents were 
normally 30,000V.  Tesla Currents were typically 100,000V - 250,000V.  Oudin 
currents were typically 250kV and above.   Of those Tesla currents were 
typically a hot flaming discharge used for X-Ray purposes, and Oudin 
discharges were generally reserved for therapeutic uses as a very high 
voltage but low current "spray" of electricity.

Some early wiring diagrams for these coil can be seen here:

By the 1930s, Oudin Coils were generally any large cylindrical Tesla Coil.
I have several plans for these from magazines that I can put on the site.

The output of the original Oudin resonators is ... "different".  When you 
use very high voltages and low currents to excite Tesla Coils you get a lot 
of beautiful effluves and corona effects but the actual sparks are reduced 
greatly.  Instead of a lightning show you get more of a St. Elmo's Fire 
show...which is still interesting.  Since few caps can handle a tank circuit 
of 50 or 100kV, normally small leyden jars are used creating a very high 
frequency circuit in the megahertz range...
A few of the early units used Franklin plates instead of leyden jars, which 
was simply an air-insulated capacitor of two metal plates 14x18" or so 
mounted on slides to adjust the distance between them.

Jeff Behary, c/o
The Turn Of The Century Electrotherapy Museum

>Hey everybody,
>      What is an Oudin coil?  Somebody told me you can put a much higher
>input voltage into one that a conventional TC, therefore getting a higher
>voltage out, but I do not know if they were correct.  Thanks.
>Scott Bogard.

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