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Re: AC Resistance (formerly Spice Simulation Pictures)
At 05:25 AM 10/31/96 +0000, you wrote:
>> Subject: Re: Spice simulation pictures
>
>From bert.hickman-at-aquila-dot-comWed Oct 30 22:04:11 1996
>Date: Wed, 30 Oct 1996 18:14:25 -0800
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: AC Resistance (formerly Spice Simulation Pictures)
>
>Tesla List wrote:
><SNIP>
>>
>> >From couturejh-at-worldnet.att-dot-netTue Oct 29 22:49:50 1996
>> Date: Tue, 29 Oct 1996 19:34:48 +0000
>> From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
>> To: tesla-at-pupman-dot-com
>> Subject: Re: Spice simulation pictures
>>
>
> Big snip ------------------------------------
>
>
>Given the above parameters, what does your graph predict for Rac?
>
>Safe computin' to ya, Jack!
>
>-- Bert --
>
>-------------------------------------------------
Bert -
Your data did not include the Q factor of your coil. The 82.6 ohms you give
for the Rac value would give a Q factor of 495 which is unrealistic for your
coil.
Q factor = 6.283 LF/R = 6.283 (.07113)(91000)/(82.6) = 492
The program gives 2040 ohms for the Reff of your coil and this would give 20
for the Q factor which is more realistic.
Q factor = 6.283(.07113)(91000)/(2040) = 20
It is obvious that Rac can not be used to find the Q factor. What is needed
is an effective resistance Reff (something that works). I have found Reff
values for various Tesla coils to develop a graph that appears to work as
shown above. This information was obtained by using data on Q factors from
Henney's and other books and back-figuring for the Reff. The graph, Fig 6,
is shown in the Tesla Coil Notebook. I am sending you a copy by snail mail.
This graph shows 290 ohms for an 1800 watt coil compared to 2040 ohms in the
printout for your coil of 1800 watts. If you can explain this difference in
ohmic values between the graph and program for the same input wattage you
have a thorough knowledge of how the program works and of Tesla coil theory.
In the equation R = 6.283 LF/Q note that the R varies directly as the
inductance L. Your L (using 980 turns) is much greater than the typical coil
L (using 400 turns) that the the graph is based upon so the Reff resistance
is greater and the JHCTES program allows for this increase. However, this is
not the complete story. The Reff is also affected by other parameters and
these must all be coordinated in any program and to make a workable graph.
It was important to have a proper Q factor and Reff in the JHCTES program
because other important program parameters could be found using the proper Q
and Reff. The graph was made by calculating Reff values for typical coils
with known chacteristics. Only the use of the graph and time will tell us
about its accuracy.
For example, with the graph it is possible to find the critical (Rp = Rs) or
other coupling even before the coil is built. As I mention in one of my
other posts the coupling must be coordinated with the gap break 'ON' time to
obtain maximum output and spark length.
An important consideration is to assure that any combinations of typical
coils using these Reff values do not end up with values for Reff that are
less than Rdc or Rac which would be unrealistic. To avoid this condition the
program modifies the information from the graph so an unrealistic Reff
resistance for a realistic coil will not occur in the program.
The graph needs to be verified by much more coil testing but so far coilers
have not taken the time to study these parameters to improve their Tesla
coils. To my knowledge this in the only graph that has ever been made for
this elusive Reff parameter. As the Reff is a rsistance and determines the
output, spark length, and overall efficiency of the Tesla coil system it is
important that this parameter be given extra attention and optimized during
the design stage.
Understanding and studying the Reff parameter would give the advanced
coilers a means of increasing the spark length and overall efficiency of
their coils. It is apparent that as we learn more about the Reff resistance
of Tesla coils we can design the coils to produce more output and be more
efficient.
Jack C.