I have finished my Fo calculation program (E-Tesla) and I have posted it to
my site at:
You can input the dimensions of your coil's secondary system and it will
estimate the total capacitance and Fo frequency. It will do one or two
terminals and flat or cone primary configurations. The dimensions can be
in standard or metric measure.
It is written in the old MS BASIC but it will serve as a basis for faster
versions written in other languages (I am not a computer programmer :-)).
There are different levels of accuracy depending on how much time you have.
The more accurate the calculations, the longer it will take. On my
system, it gets within about 2% of the actual values at accuracy level
three. Time will tell how well it does on a wider variety of coils but I
think it will do fine. As far as I know everything is working the way it
It also outputs files for the voltage and stress fields around the coil.
Excel can do nice surface plots with these files. You can modify the
program as you please, if you have some special situation, but it should
cover everything the way it is. There are other versions in the works, by
others, that will, hopefully, eliminate some of the speed and memory
limitations of BASIC.
The program works by setting up the coil boundary conditions in an x,y
array and solving the matrix by Laplace's equation. Then the E-field is
measured around the coil and extrapolated to find the total E-field normal
to the surface of a virtual sphere around the coil. The charge inside the
sphere is then known and the initial voltage is also known so the
capacitance is the ratio of charge over voltage. There are no fudge
factors or anything like that, it is all pure applied field theory.
This BASIC program is free and public domain. If you can use it as part of
something or can improve it, feel free to do so.
I hope this program and some of the more refined programs to follow will
help solve the problem of estimating the resonant frequency of the
secondary. It will also provide a way for people without test equipment to
get a pretty good idea of what frequency their coils run at.
I will try to answer questions, comments, problems, etc. off-list at
<terryf-at-verinet-dot-com> . I tested everything as well as I could on my
system. If you do have a problem, please send me the file OUTPUT.TXT
generated by the program. It has all the vital parameters in it.
Hopefully, I can figure out what is going on from that file.
My special thanks to Jim Monte for providing many great tips and comments
that went into this program.
Have fun with this program. It was a lot of fun to write even if I didn't
really know what I was doing :-))