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Re: 10 tests and suddenly...RRRAAAATTTTT!!!

Subject:      Re: 10 tests and suddenly...RRRAAAATTTTT!!!
       Date:  Sun, 11 May 1997 12:51:23 -0700
       From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
         To:  Tesla List <tesla-at-pupman-dot-com>
 References: 
            1


Tesla List wrote:
> 
> Subject:  10 tests and suddenly...RRRAAAATTTTT!!!
>   Date:  Sun, 11 May 1997 03:42:01 +0200
>   From:  tesla <tesla-at-ixx.se>
>     To:  tesla-at-pupman-dot-com
> 
> Hi all.
> 
> Just returned from my test site and now i believe i can't stop doing
> this
> anymore. Yep, just got my coil working after 9 or so miserably
> unsuccessful testruns. Here's the specs :
> 
> Primary : 10 turns of 0,8mm coppertubing and 1cm spacing
>            Angle : 5%
> 
> Secondary : 1000 turns of 0,6mm enamled copperwire
>              Height : 60cm
>              Diameter : 16.5mm (0,4mm walled PVC pipe)
> 
> Cap : Homerolled poly cap. 29,3nF approx. capable of 20kV pulse
>         (Very overdimensioned!! Just in case)
> 
> Transformer(s) : 6 4kV/45mA transformers wired in series and paralell
>                  for a total output of 8kV/135mA. About 1,08kVA
> 
> Other : Toroid - Dia : 70cm x 11,5cm covered with aluminumfoil
>          Spark gap : R.Q with 7 electrodes and 12V high speed fan.
> 
<SNIP>
 I went to the variac and cranked it up when
> suddenly......KKKKRRRRRAAATTTT.
> Some really fat purple and white arcs jumped around the toroid and some
> shot of to the lifting jack. I was STUNNED! 3-4 footers continously!!
> 
> Now this might not seem very impressive to some of you experienced guys
> but to me, with all my failed tests this is a real big leap forward.
> I'm off to coiling heaven. Nothing(except power) will stop me now. I'm
> hooked!
> It sure is one thing to see pictures of a running coil and experience  > it live!
> The sound it produces is really agressive.

<SNIP>

Congratulations on first light, Matt! There's really nothing like seeing
(and hearing!) the coil you've built from scratch really work! From the
sounds of it, you'll really need that strike rail again!

> I won't bore you anymore with this but instead i've got a question
> regarding the cap.
> Why is it that the capacitance recommended by different programs and
> even the
> "hand" calculated values are way too big?? The only way to get it near
> the "correct" value is dividing it by two.
> I think i must agree with Richard Hull here. Theory and practice are > two very different things, yet one can't live without the other.
> 
> I'm off rebuilding things, see you later.....   =)
> 
> //Matt


I assume you meant your coil diameter was 16.5cm and not 16.5 mm. :^).
For my conveniance, I've converted the Metric values to English. I've
also tried to "read between the lines" on your coil parameters. 

Toroid: 27.5" x 4.5"
Est. Toroid Capacitance (20% derating assumed) ~ 19pF
Secondary: 24 AWG, 23.6" high, 1000 turns, 6.5" outside diameter
Estimated secondary Inductance ~ 40.5 mH
Estimated secondary Self-Capacitance ~ 10.5 pF
Estimated Unloaded secondary Fo ~ 244 kHz
Estimated Loaded (secondary + toroid) Fo ~ 146 kHz

(Note: Have you tried measuring your actual secondary-toroid Fo with a
signal generator and LED-pair?)

Primary: Tubing Diameter = 0.3"
Ctr-Ctr Spacing = 0.39 + 0.3 = 0.69" (Assumed)
Inner diameter: 8"  (Assumed)
Number of Turns:  10
Estimated Inductance = 41 uH
Primary Cap Size = 29.3 nF = 0.0293 uF
Primary Fo ~ 145 kHz

(Note: I assumed you meant you had 1 cm of clearance between primary
turns... If your ctr-ctr spacing was only 1 cm, I can understand why you
might be running into primary turn-turn arc-over problems).  

Conclusion: Primary Fo ~ Loaded Secondary Fo ~ 145 kHz. Lookin' Good!

>From the looks of it, the parameters you're using look to be "right on"
for a good running coil! Are any of the above assumptions I've made in
error? If not, compare the various values with what your calculated
values are, and we can see where any problems lie in your design tools. 
Relative to basic 2-coil design, the basic design parameters are pretty
well "shaken down", and practice pretty closely matches theory. It's
when you get into the subtleties or try to maximize sparklength versus
input power that the "black magic" starts creeping in... :^).

Good luck, and safe coilin' to you, Matt!

-- Bert --