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Re: Info and requests for book




From: 	Mark S. Rzeszotarski, Ph.D.[SMTP:msr7-at-po.cwru.edu]
Sent: 	Wednesday, September 17, 1997 2:27 AM
To: 	Tesla List
Subject: 	Re: Info and requests for book

Hello all:
Terry Fritz said in part:
<snip>
> If any one has a "wish list" of things they would like to see in
>a Tesla Coil design book please drop me an E-mail at "terryf-at-verinet-dot-com" .
>>From what I have seen here and in the archives it looks like capacitors,
>secondary inductors, and power sources are the big issues.  I guess I am
>somewhat surprised that there is so little theory.
        I guess I am considered one of the more theoretical folks on the
list and have in fact worked a lot towards a mathematical understanding of
the tesla coil.  I have written simulations for mutual inductance, helical
resonance, proximity effects, optimal coil geometries, and a host of other
topics.  Each topic leads me back to the lab for experimentation.  There are
fine theoretical works out there such as the Corum brothers references, but
these theories fall quite short when the sparks break out.  The bottom line
is that I am skeptical that any one person can write an authoritative text
on the subject at this time.  I find myself doing more experiments in the
lab to confirm theory than vice versa.  Things get quite nonlinear when the
sparks fly.  I agree that there are lots of useful texts/manuals out there
and that each has limitations and omissions at the present time.
        Much of what you see posted on the list is due to the continual
addition of newbies who need guidance on basic issues.  A lot of the higher
level discussions occur off-list on a person-to-person basis to minimize
bandwidth and prevent the inevitable newbie questions which occur when these
things are posted to the general list.  I probably send 25 personal E-mails
relating to tesla coil research for every one I post to the list.

>I am looking for any info on the following:
>1.      Any information on the losses on the secondary such as secondary
>terminal capacitance change vs voltage, Energy loss vs voltage and time,
>ect. would be useful.
        Do you have a really good method for measuring the voltage of a
tesla coil during spark breakout?  If so, I am interested.  I do not have a
model for this either.  Recent off-list discussions suggest that sparks
introduce additional top capacitance on the order of 1-3 pF per foot of spark.

>2.      Has anyone tried using varistors (transient surge absorbers) instead
>of spark gaps for transformer protection?  I realize they my need to be
>isolated with chokes due to their capacitance but in quantity they are
>fairly inexpensive (1800V 4500A $1.88ea from DigiKey) and they can be easily
>chained together to reach a desired voltage.  I would think they would give
>much better protection than a spark gap.
        They are worth investigating, but I have my doubts.  How do they
perform at RF frequencies?  Can they switch on fast enough?  Will a
resistive voltage divider work once these things start to turn on?  Peak
kickback can be more than three times the peak A.C. output voltage of the
transformer.

>3.      Any info on predicting secondary parasitic capacitance or resonant
>frequency.  This is a big killer for most Tesla coils and the info I have
>seen tends to fall far short of what is needed.  There are certainly better
>ways to wind the secondary to reduce this capacitance but I have never seen
>any good details on doing this.  The programs and equations I have seen have
>never predicted any of my coils very well at all.  Virtually all Tesla coils
>tend to be big delay lines instead of antennas.
        Distributed capacitance is easily modelled and is essentially
isotropic in nature, related to the area of the coil on the former.  It is
not turns dependent.  It is not a killer unless you build really big coils,
and top capacitance does much to tame it.

>I guess I am one of those who never saw too much mystery in how Tesla coils
>worked (although getting all the variables to work together is a challenge).
>I guess it is time to finally put this all in some kind of book.  I hope
>this doesn't take too much of the magic out of Tesla coiling but I feel that
>there needs to be better basic info.  Thoughts / Comments  let me know.
        Good luck with your book.  I for one feel there is still a lot of
mystery in tesla coils and am still learning a lot about them each week.  My
computer simulations help me confirm what is going on, but fall short when
it comes to predicting performance.  Make sure you include a design for a
really killer coil system in your text, since that is what mose newbies
want.  You may want to post one to the list for constructive comments, to
verify that it is indeed a great performer.
Best Regards,
Mark S. Rzeszotarski, Ph.D.