Re: Inductance of a conical coil

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

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Antonio,

At what frequency does the coil resonate at? I'm not sure how a flat 
primary distributes current at low vs. high frequency's (the calc's are low 
freq inductance's). I don't know how much has been studied in the primary 
arena for the typical geometry's we use. Considering the low inductance's, 
it may not take much to make a significant change, but possibly the 
external cap may make for an even distribution.

Take care,
Bart

Tesla list wrote:

>Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
>
>Tesla list wrote:
>
> > Original poster: "Barton B. Anderson by way of Terry Fritz 
> <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
>
> > Nature will know, but how accurate is your meter and can it read that low?
>
>I don't have an inductance meter. To measure inductance, I resonate the
>coil with a known capacitor. A problem may be the influence of
>connection
>wiring in these measurements of uH inductances.
>I made a flat spiral coil today, to be used with the secondary that I
>used in my transformerless coils in a conventional Tesla coil.
>I planned it to have 58.4 uH, by Wheeler's formula. Fantc predicts a
>bit less: 57.3 uH. The dimensions of the coil were: rmin=7 cm,
>rmax=12.5 cm, 14.7 turns, #18 wire (more than enough for the case).
>The design coupling coefficient with the secondary was 0.105, for
>mode 9:10.
>The measured coil measured as 60.20 uH, and the resulting coupling
>coefficient for the design geometry ended as 0.125, lowering the
>operating mode to close to 7:8.
>Looking at what was wrong, I noticed that to obtain this inductance
>I have just to increase the number of turns to 14.93. This is less
>than 20 cm of wire, and in the measurements I certainly had more than
>this. The increased coupling is more puzzling, but it was evidently
>changing depending on how I was arranging the connections of the
>coils. Theoretically, I could obtain this by rising the primary
>coil by less than 1 cm.
>The coil worked very well as primary in initial tests. I tuned the
>coil by changing the length of an antenna in the secondary terminal,
>as I prefer to do. 15-20 cm multiple streamers at the antenna tip,
>with a 5 nF primary capacitor and a 5000 V, 30 mA NST. A bit better
>that what I obtain with a directly coupled version (that operates in
>a much slower mode). I will set up a page showing the coil soon.
>
> > I was thinking about the flat spiral case. Have you considered looking at a
> > mutlilayer formula? By "concept", the flat spiral is similar to a
> > multilayer coil, except the length of the coil doesn't really play a
> > significant role since the length becomes the wire size. I expect
> > multilayer formula's are derivitives of Wheeler, so maybe just stripping
> > down of what is not needed.
>
>Maybe. I will take a look.
>
>Antonio Carlos M. de Queiroz
>
>
>
>