Re: TC Critical Coupling

To: tesla-at-pupman-dot-com
Subject: Re: TC Critical Coupling
From: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Fri, 07 May 1999 11:41:35 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

  Terry -

 Thank you for your reply to my post. How do you find the time to do all
this work for the Tesla List? We all appreciate your efforts in keeping us
informed.

  I do not wish to imply that your coil is not "optimal". In fact I do not
know what would comprise an optimal Tesla coil. A random extra long spark
certainly is not a proper scientific way to rate a TC. In my Tesla Coil
Notebook I mention that the critically coupled TC may not give maximum spark
length because other TC parameter combinations are more effective in
producing spark length. Note, however, that Terman said maximum secondary
current, not voltage. Spark length is due to voltage. In other words the
critically coupled TC may give more current or power but not necessarily
longer sparks than the non-critically coupled TC.

  The reason that your JHCTES printout was different than mine was because
you used a different input. That was my fault. Sorry about that. I should
have mentioned that the primary was a coil not a spiral. If you make this
change and change the 10.10 to 4.00 you will get the same outputs I got. The
effective resistances will be Rp=Rs=92 ohms. Note that this is the effective
resistance not a DC resistance. The DC resistance does not work with other
equations in the program. I noticed you did not use the resistances in your
program. 

  All of the parameter values shown in the program must work with all of the
equations in the program if the TC system is to be coordinated and in tune.
This makes developing a TC computer program like the JHCTES difficult to
accomplish and obviously why it stands alone for the time being. The program
appears to be deceptively simple but in fact takes some knowledge of how a
Tesla coil operates to get the most benefit from it. It has the great
advantage that it is based on both theory and data from real world coils.
The JHCTES program is only for classical Tesla coils. Ther are no similar
computer programs for other types of Tesla coils mainly because there is not
enough empirical (real world) data.

  Raising the secondary can be used to find the critical coupling point but
this is self defeating because it reduces the magnetic flux linkages which
reduces the TC output. For optimal power output the TC must be designed
correctly from the start in order that the secondary does not have to be
raised to make it work at all, usually to prevent sparkovers.  

  The 830 primary amps and the 32.4 secondary amps are instantaneous peak
amps. In my TC Notebook I show how the primary amps are found.

   Ip = Vp sqrt(Cp/Lp)
 
  These instantaneous amps are high and the reason the primary wiring must
be large. Note that the magnetic flux from the primary coil is dependent on
the turns times the amps. Using more turns as some coilers recommend would
not help if the primary wiring was large enough for the current. In fact the
added resistance of more turns would reduce the magnetic flux and the TC
output.

  Thank you again for replying to my post.

  John Couture

---------------------------- 

At 08:31 PM 5/5/99 -0600, you wrote:
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>Hi John,
>
>Always good to hear from you.
>
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