Re: Bart's Coil

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

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
--
Barton B. Anderson
http://www.classictesla-dot-com

Tesla list wrote:

> 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 mutual inductance tests. It looks like the programs
> are amazingly close to the test values. Your test values of 11.04 amps and
> 2.72 volts gives Lm = 653.52. The JHCTES gives 617.76 for Lm. I would expect
> that the JHCTES value to be lower because this is for when the bottom of the
> secondary coil is on the same level as the primary. When the secondary is
> lowered the Lm and the K would become larger.
>
> I plan to change the JHCTES program to include negative distance values in
> the near future so comparisons can be made on an equal basis. I agree that
> the K appears to be in the .159 and .169 range.
>
> There is a relatively easy test that directly tests for the K factor and
> eliminates the inaccuracies caused by the three variables, Lm, Lp, and Ls
> when calculating K. This test only requires a function generator, frequency
> counter, and oscilloscope and is shown in my TCC Guide page 14-11 of which I
> believe you have a copy. The equation is
>
>               K = sqrt(1-(Fo/Fs)^2)
>
> The function generator is used to feed a signal into the primary coil. There
> will be two resonant frequencies Fo and Fs when the unloaded (no toroid)
> secondary coil is open (Fo) and when it is shorted (Fs). The two frequencies
> are usually just below the loaded resonant frequency. The oscilloscope will
> indicate the two frequencies. The test is sensitive to the surrounding
> conditions.
>
>  I have not tried this on a coil of your size but it works good on small
> coils. I would be interested in the results if you get a chance to do this
> test.
>
> John Couture