Mutual Inductance (was Flat Primary Winding - next question)

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Tuesday, June 23, 1998 5:25 PM
To:  Tesla List
Subject:  Re: Mutual Inductance (was Flat Primary Winding - next    question)

  Terry -

  Many thanks for your comments on the JHCTES computer program and the
additional information regarding the parameters of your coil. I was pleased
to find that the program K = .21 gave an accuracy of 1.5% with the K = .204
of the test. I must admit that this very favorable accuracy is unusual for
the program. From your comments it is obvious you have a good understanding
of how the JHCTES program works.

  I agree that Mark's program has the advantage of predicting the K factors
at various secondary heights. The original JHCTES program included this
parameter as "x" in older programs. However, because of lack of empirical
data and the fact that the same effect of raising the secondary could be
accomplished in the design of the primary coil this parameter was omitted in
the newer versions.

  The new Ver 2.3 program gives recommended pri/sec clearances as a default
and raising the secondary was considered unnecessary when the proper
clearences are used.. For example, the reccommended clearance for this coil
is about 3 inches. (avg rad = 12.4, width = 8.0, turns = 11.64, Lp = 111 uh,
and K = .17 coupling). The pri inductance, oper freq and spark length are
the same but the added clearance would avoid sparkovers between the pri and
sec coils. The K Factor is changed but this does not change the amount of
energy transfered and would not change the spark length.

Raising the secondary coil also changes the tuning of the system and changes
the operating frequency. In the past some tests involving raising the
secondary gave better tuning and spark length compared to the non raised
untuned condition. This was misinterpreted as raising the sec to be an
advantage. Do you know why raising the secondary changes the quenching? Is
there a math relationship?

 It should be noted that quenching is not a part of the JHCTES program. To
my knowledge no one has ever developed a program that included the operating
spark gap, quenching, and the approximate dozen other parameters involved.
This would require a large number of building and testing of coils to obtain
the necessary data..  

  However, raising the secondary is still a controversial issue with coilers
that only empirical data from testing real coils can settle. Adding the "x"
dimension to the JHCTES program could easily be done in the future if
testing indicates it is an advantage and what parameters are changed.

  John Couture


At 11:46 PM 6/21/98 -0500, you wrote:
>From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
>Sent:  Sunday, June 21, 1998 12:13 AM
>To:  Tesla List
>Subject:  Re: Mutual Inductance (was Flat Primary Winding - next   question)
>Just for clarity,
>The coil in case A has the following parameters:
>15,000 volt 60 mA neon input (variac controlled)
>17.05nF primary cap
>8.84 inch avarage radius flat spiral primary of 1/4 inch tubing.
>5.67 inch wide coil section
>Lp = 118.4 uH
>Fo = 112.0 kHz
>5.13 inch radius
>1000 turns
>33.33 turns per inch
>0.02002 bare wire diameter
>Ls = 75.4 mH
>Cself = 16.68 pF
>Ctop = 10.10 pF
>The JHCTES program gives a K of 0.21 and m = 602.04 uH.
>Mark's program gives a K of 2.01 and m = 635.96 uH.
>The actual K is 0.2069 and m is 618.19 uH.
>The thing I really like about Mark's program is that it predicts K for
>various coil heights.
>My coil will not quench well with a K of 0.21.  I have to raise the coil
>about 2 inches to get a clean quench.
>Mark's program very accurately predicts the K at various heights.  The
>JHCTES program omits this input because of "lack of emperical data" (page
>11-1 Tesla Coil notebook).  Perhaps John could add this feature to JHCTES??  
>        Terry Fritz
>At 08:09 PM 6/20/98 -0500, you wrote:
>>From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
>>Sent:  Saturday, June 20, 1998 3:01 PM
>>To:  Tesla List
>>Subject:  Re: Mutual Inductance (was Flat Primary Winding - next  question)
>>  All -
>>  The mutual inductance of a Tesla coil is important because it is the major
>>parameter that connects the two magnetic circuits of the primary and
>>secondary tank systems. Mutual inductance can be used to find other
>>parameters including the important K factor or coupling of the coils.
>>      K = Lm / sqrt(Lp x Ls)
>>  It is always interesting to compare different methods of finding TC
>>parameters like the mutual inductance. Mark has listed below the mutual
>>inductance he has found for different primary coil arrangements. To compare
>>his data using the JHCTES program I came up with the following for System A:
---------------------------------  big snip