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Re: Windings vs. Diameter

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Curt,
When wire is wound it tends to twist and roll some leaving spaces between the windings so there are a lot of charts around that predict how much space that is. 

Page 8 below is a very common chart that lists #30 wire at 90.5 Turns Per Inch.

http://hot-streamer.com/temp/FormulasForTeslaCoils.pdf

Here is the Nexans chart:

Winding percentages:
AWG             %
10-11           99
12-13           98
14-15           97
16-17           96
18-19           95
20-21           94
22-23           93
24-28           92
29-33           91
34-38           90
39-42           89
43              88
Of course, when I started the wind and could see this space, so I used my finger to force them together. If I had not done that then the chart might have been very good!! But it looks like I was able to push out "all" the space between the windings. 99.9999% of the coils on earth are machine wound so the chart is probably fine.
However for Tesla coil secondaries, we almost always do them by hand so there can be significant differences in turns per inch. We run into the problem when trying to predict secondary inductances using standard turns per inch charts. There is also a significant variation in wire coating thicknesses. I never had a good feel for how much this variation could be until now. it can probably make a 20% difference in the secondary coil inductance!!
Hardly anyone ever really "counts" the turns exactly, so we always have to guess... I knew that there was a lot of variation but know I know "why" *:-)) The next time I have to figure out someone's secondary coil, I will add this to the questions I ask ;-)) If they just let the wire fall naturally, then the chart above is good. If they pushed the windings together, then it is a pure wire diameter x distance thing. And that is a big difference!! 

Cheers,

        Terry

At 01:56 PM 6/30/2006, you wrote:

Terry,

Where did you get the 91% number from?  I'm
confused...

You coil looks great...

Curt.


--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: Vardan
> <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> Just for the record...
>
> The coil I just wound:
>
> http://drsstc.com/~sisg/files/SISG-coil/P6290127.JPG
>
> is 11.50 long with #30 wire.  There are 985.00 turns
> on it via digital counter.
>
> The wire is 0.0116 inches in diameter via a new
> Starrett 436 micrometer.
>
> 985 x 0.0116 = 11.426 inches.  Pretty close ;-))  I
> pushed the wire
> with a finger nail all the way during the wind so it
> is tight and the
> wire torque was high.  The wire is "cheap" and had a
> few rough spots
> I could feel as it was going out my fingers.
>
> There is a "wiring percentage" number of 91% for
> this wire that seems
> all wrong...
>
> If you can measure the wire diameter really well and
> wind it tight
> and forced, the "wire diameter x turns" seems to
> work out just
> fine...  Thin wire like this forces more easily than
> thicker...
>
> Cheers,
>
>       Terry
>
>
>


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