RE: Bart's Coil

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Bart -

Thank you for making the K Factor Test. It looks like the K of your coil is
definitely 0.165 and the 653.52 is the correct mutual inductance. This is
proof that these two tests can certainly be used to find these two
parameters accurately when tests are properly made. I admit the tests are
not easy to perform and you did a good job.

The reason I wasn't sure that you could make the test is because when the K
becomes smaller (looser coupling) the two frequencies get closer together
and it is harder to read the frequencies. A frequency counter would make it
easier to read the frequencies than an oscilloscope. Note that it is a
coincidence that the operating frequency is near these two frequencies.
Changing the toroid size would change the operating frequency but not the K
factor frequencies.

Several years ago I made a rough graph of the K factor vs Fo/Fs ratios. It
is obvious from the graph that for K's lower than 0.2 the two frequencies
get very close together. As an example when the K = 0.165 the ratio of Fo/Fs
is 0.986 (7.2/7.3) and when K = 0.10 the ratio is 0.995, a difference that
will require careful measuring. For the graph click on

       www.mgte-dot-com/graph10.pdf

You will need Acrobat 4 or 5 (free) to review and print the graph. I lived
in California when I made the graph but now live in Jacksonville Florida.

Here is an unsolved problem for advanced coilers. What is the relationship
between the resonant frequency of the unloaded secondary coil (114.56 KHz)
and the open secondary (unloaded) test frequency Fo (68.493 KHz)? Is there a
theoretical equation that relates these parameters?

John Couture

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

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, November 27, 2001 6:54 AM
To: tesla-at-pupman-dot-com
Subject: Re: Bart's Coil


Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi John,

Ok..  I don't have a generator on site, but no worrys, I used Terry's TCT
to feed a signal into the
primary (another use for the little beast). I then used my scope to find Fo
and Fs with top load
removed. Signal came up nice and strong. The scope is analog (counting
squares and ticks). I spent
quite a while back and forth with the measurement to be as accurate as
possible. Here's the data.

Fo = 68.493 kHz (7.2 sq. -at- 2us/div)
Fs = 69.444 kHz (7.3 sq. -at- 2us/div)

Using, K = sqrt(1-(Fo/Fs)^2), then K = 0.165 and Lm = 653.52

The fact that the difference between 7.2 and 7.3 squares happened to be
exactly what I measured
previously is odd coincidence (since my eyes can't accurately go to a finer
detail). However, this
method obviously works just fine as long as the user can see the difference.

It would be more accurate with a scope that can capture the signal and not
be dependent on my eyes. If
I can grab a better scope from work this week, I'll give it another go.

Take care,
Bart
--