RE: Tesla Coil Blunders

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>


Dunckx -

Thank you for the info on your web site. I agree the log decrement, Q factor
and the R are all equated by the equations you show, however, I believe this
R is a different R then the one I am referring to. For example:

   Your    R = 6.283 F L/Q

   My      R = 2L x sqrt( 1/LC - (6.283 F^2))

In the data I have collected tests indicate that the TC secondary coil has
two resonant frequencies depending on how you do the test. A low voltage,
low current test or a high voltage, high current operating test. The latter
test gives a resonant frequency that is about 10 to 15 percent lower. The
low voltage test when properly done gives a resonant frequency that agrees
with the Wheeler/Medhurst equations to around one percent. You can easily
check this with the on line JHCTES Ver 3.2 program and other similar
programs. I have not had time to check this with the ETesla6 program.

John Couture

----------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, March 28, 2001 4:00 PM
To: tesla-at-pupman-dot-com
Subject: Re: Tesla Coil Blunders


Original poster: "Dr. Duncan Cadd by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi John!

>To my knowledge no one has ever determined how to find this very
important
>"R" for an operating Tesla coil either by calculation or by tests. TC
>programs are hurting because of this lack of information.If anyone
has any
>comments I would be interested in them.


You can get this from the ringdown time (via logarithmic decrement) of
the isolated secondary (i.e. get the primary out of the loop) as the R
determines the damping.  I can't reproduce all the maths here, but
it's on my page at:

http://home.freeuk-dot-net/dunckx/wireless/sparktx/sparktx.html

The relevant bit starts around half way down the page.  You can
measure the log decrement either by means of an absorption wavemeter
(and I'm sure Ed Phillips would just love to tell you how :-) or by
recording the ringdown on a suitable scope and counting the peaks, a
shortcut to this is also on the above page (if I typed the URL
correctly ;-)

Hope this helps.

Dunckx