[Prev][Next][Index][Thread]

1/4 Wave Theories - Trash Them!




----------
From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Monday, June 01, 1998 5:27 PM
To:  Tesla List
Subject:  Re: 1/4 Wave Theories - Trash Them!

Hi Terry, all,

> From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
> Sent:  Thursday, May 28, 1998 1:05 AM
> To:  tesla-at-pupman-dot-com
> Subject:  1/4 Wave Theories - Trash Them!
> 
> Hi All,
> 
>        I wrote another paper.  What many have suspected, appears to be true.
> Tesla Coils are not antennas.  They are transformers.
> 
> "An Analysis of Top and Bottom Currents in the Tesla Coil Secondary Inductor."
> 
> It can be found as a web page and WORD97 zip at:
> 
> http://www.peakpeak-dot-com/~terryf/tesla/experiments/experiments.html
> 
>     This paper describes measurements of the top and bottom currents in a Tesla
> coil secondary inductor.  These measurements indicate that the secondary is
> acting as a simple lumped inductor.  There appears to be no 1/4 wave effect.
> The currents are in phase.  It appears that the 1/4 wave theory of Tesla
> coil operation is incorrect.  Also, the top terminal appears to be acting as
> a simple capacitor in parallel with the coil's self capacitance.  A model
> for this behavior is presented.
> 
>         You can take all those 1/4 wave models and all those books with
> pretty sine wave current distributions and throw them away (Well.... save
> Tesla's)!  The basic Tesla coil is a simple lumped parameter transformer
> with loose coupling.  Very good news for spice modelers!
> 
> Still need to do some theorizing about the self capacitance........
> 
> 
> 
> Now.... comes the sparks!! :-))
> 
> 
>         Terry Fritz

I think there is no doubt this is true when the gap is conducting. 
The Corums say this as well. I should point out however that in a 
lumped circuit, not only should the phasing criteria be met but the 
currents at top and bottom should also be identical as in a closed 
circuit (when NO output discharge is issuing). Is this the case? I 
suspect not. The Corums say that this is because the coil, being much 
shorter physically than the operating wavelength, is immersed in the 
primary field. I pointed out to Ken that coupling is virtually non-
existent at the top turns. He pooh-poohed this as incorrect thinking.
Guys and gals, knowing what we now do about magnifiers, I suggest 
the lack-of-k-at-the-top argument demonstrably does have merit. 
     The nub of C&C's argument is that the resonator mode occurs when 
the gap has gone out. However, I am sure from my own experiments that 
this argument is passe - no-one can put the gap out without a 
secondary discharge issuing and without incurring serious losses in 
the primary. Besides, when the gap *does* eventually go out, most of 
the energy has already disappeared from the system by one route or 
another. I still have not seen any magical voltage rise in the 
resonator e-field on captured scope waveforms at this time. 
     The nice thing about the lumped model being valid is that it 
does make engineering a system for particular output voltages 
possible. One can choose a resonator height with this in mind.
It also ties in nicely with observed single shot spark lengths.

       I hate to perpetuate what I think are basically useless ideas 
in here but I would be interested to see some top and bottom current 
measurements under no breakout conditions. All input welcome.

Malcolm