Re: my coils not up to snuff

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

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Sam,

It's likely your out of tune for such small sparks.
Some of what would be helpful to ensure your tune is in range is a little 
more detail: With what you have given, I would expect about 10 to 10.5 
turns, but without more info, there's no way to be sure (however, we can be 
sure with more information).

1) The primary outer radius (from the very center of the coil to right at 
turn 8).

2) The vertical position of the inner primary turn in relation to the 
bottom secondary turn.
If at this time it is "even", then your coupling is about 0.219 and this is 
too tight. As you come into tune, you'll begin to have problems (arc over 
and/or racing sparks along the coil). I like to set my coupling at 0.158 to 
start and then adjust the secondary manually by observation up or down 
until coupling is as tight as possible without occurrences of racing 
sparks. For your coil, 0.158 would occur with the secondary bottom turn 2" 
above the primary (I assume this is a flat primary?). Others like to start 
with tight coupling and loosen up until racing sparks go away, and yet 
others like to start loose and tighten up until racing sparks start, and 
then loosen up until they stop). It's not a big deal how you adjust 
coupling, so long as you do. BTW, some folks are happy with a smooth 
running coil that isn't set to maximum performance (not too loose and not 
too tight = somewhere in a happy medium).

3) The toroid major diameters would be helpful and their positions above 
the secondary.

4) A static gap is fine, but you "need" a fan to stabilize the arc voltage 
across the gap, otherwise, the gap will quickly heat up and reduce the arc 
voltage required to arc the gap (this can occur very fast if electrode mass 
is small).

5) Set the static gap electrode separation to your NST's arc distance 
between the outputs (this is should be your maximum total gap distance). 
Simply take the NST by itself along with your static gap. Adjust the gap 
distance to the point where the NST itself can jump across the gap. Be sure 
to "UNPLUG BETWEEN GAP ADJUSTMENTS". When the NST can arc the gap distance, 
you know your "maximum" electrode separation distance is. To go beyond this 
is asking for trouble (NST and/or cap failure is probable).

Take care,
Bart

Tesla list wrote:

>Original poster: "Sam W." <HAZAA_69-at-hotmail-dot-com>
>
>----- Original Message -----
>From: <mailto:HAZAA_69-at-hotmail-dot-com>Sam W.
>To: <mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
>Sent: Monday, December 08, 2003 3:08 PM
>
>I have a coil running on a 12/60 nst
>4.5" x 30" secondary w/21 AWG magnet wire
>Primary:8 turns of 10 AWG insulated wire
>Spark gap is a single static with no pressurized air for quenching
>mmc 25 0.33 uF caps rated at 600VAC in series to make 12500VAC 0.0133uF
>choke 200 turns 21 AWG
>4" flexible aluminum ducting covered in aluminum tape
>2" flex aluminum ducting covered in aluminum tape
>(double toroid)
>
>im getting like 3" breakout, with only 9" going to a grounded pole. I 
>couldnt get any thin walled copper tubing, so i used insulated wire rated 
>at 15 kv. if i replace the primary and change the spark gap will i get 
>bigger sparks? im reading about people with similar setups getting like 
>3-4 ft. sparks. This was my first coil, and i did it for science fair. I 
>was a little dissapointed with performance. I dont want to use a rotary 
>gap, cause i cant get a synchronous motor, and asynchs will blow my nst. 
>PLEASE HELP!
>
>
>
>