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Re: Tesla calculator frustration.

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Bill,

It is not really simple.  You need a couple of programs and a fair bit of
knowledge.  Let me "try" :-)

First I like to figure out the secondary inductance.  I just use the L(uH)
= (N x R)^2 / (9R + 10H) formula from Matt's site but many programs do it too:


I get 35.85mH for your secondary coil's inductance.

Then you need to know the resonant frequency of your system with E-Tesla6.
I typed the following into E-Tesla6.  I had to guess at a few numbers.
Your 4 inch spaced pizza pans will not matter really but you should use the
center of them for the terminal height in E-Telsa6.

 E-TESLA  V6.11C  November 21, 2000 
 Grid Size = 200.000000
 Scale Multiplier = 1.000000
 Terminated Coil
 Ceiling Distance = 100.000000
 Wall Distance = 50.000000
 Primary Height (Inner Turn) = 12.000000
 Primary Inner Diameter = 9.750000
 Primary Outer Diameter = 24.000000
 Primary Height (Outer Turn) = 12.000000
 Strike Rail Height = 0.000000
 Strike Rail Diameter = 0.000000
 Secondary Base Height = 12.000000
 Secondary Diameter = 6.625000
 Secondary Length = 27.625000
 Secondary Inductance (mH) = 35.850000
 Terminal-1 Height (center) = 45.000000
 Terminal-1 Cord Diameter = 8.000000
 Terminal-1 C-C Diameter (toroid only)= 23.500000
 Terminal-2 Height (center) = 45.000000
 Terminal-2 Cord Diameter = 0.000000
 Terminal-2 C-C Diameter (toroid only)= 0.000000
 Top Voltage = 100.000000
 Pass     Ccalc (pF)          Change            Fcalc (Hz)
  1000   C=18.37255       Err%=1837154.625000       F=196105.98
  2000   C=30.79789       Err%=67.629959       F=151465.97
 27000   C=43.10861       Err%=0.000491       F=128024.63
 28000   C=43.10872       Err%=0.000266       F=128024.46
 29000   C=43.10874       Err%=0.000024       F=128024.45

Ok so we get 128.0kHz as the secondary system frequency.

No you can select from all kinds of programs.  I'll us my silly one since
it is "mine" and "I" like it ;-))  But there are far far better ones...
Mine needs the dos screen font and all set up which is a pain... (read the
directions if you try it)


Note this picture of the program's output:


Now you need to separate the total secondary capacitance (43.10874pF) from
the Medhurst (secondary self capacitance) capacitance (12.23328 from my
program).  You just subtract:

43.10874 - 12.23328 = 30.875pF which is the effective "top load"
capacitance.  Note that the secondary frequency (in my program) is now
128.0 :-)))  Of course, "my" programs always work out :-)))

The green number by the primary turns is the tap point of 7.34 turns which
is the answer you seek and assuming I used the right numbers and did not goof.

A check is that the secondary and primary frequencies match.  Of course,
you may have to adjust the tap point a little for streamer loading and room
effects but it will be really close.

E-Tesla6 kind of threw a monkey wrench into many programs in that it
suddenly provided a way to find the resonant frequency, and top load
capacitance.  Most existing programs were not ready for this and they have
not caught up yet, so it is still a bit messy...  If you want one of the
most advanced programs, check out Kurt's:

(needs Excel to run)

I am sure the programs will catch up pretty quick once we stop changing the
rules all the time ;-))

Hope this helps.



At 05:38 PM 5/30/2001 -0400, you wrote:
>This really should be quite simple, but no...
>I just want to calculate where I *should* tap my primary, given the
>Cap: 0.06uF
>Primary: Inner diameter = 9.75", 1/2" spacing (center to center), 1/4"
>Secondary: 1000 turns, 27.625" winding length, 6.625" diameter.
>Topload: 8" chord, 23.5" center to center (capacitance = 34.845?)
>Previously (with a smaller topload), I managed (or so I thought) to do
>the calculation using JHCTES version 3.2, at
>but now I can't see how I ever did it.  The weird thing here is that
>what I would logically like to specify as input parameters, like primary
>interturn spacing, are output parameters.  I have to try to adjust the
>input parameters to get output parameters that match my existing
>I've also tried E-Tesla 5 and 6 - got significantly different results,
>and don't quite see how to calculate my tap point anyway.
>Are the specs I've listed sufficient for calculating the tap point?
>Another question, about toroid topload shape:  I made mine from 8" dryer
>duct and two 16" pizza pans, but the pizza pans are about 4" apart. 
>Should that be a problem?  Any idea how much that affects the toploads
>	Thanks again,
>	Bill V.