Re: Building a new coil

From: 	Chuck Curran[SMTP:ccurran-at-execpc-dot-com]
Sent: 	Monday, June 23, 1997 9:23 PM
To: 	Tesla List
Subject: 	Re: Building a new coil

Tesla List wrote:
> From:   Rodney Davies[SMTP:rgd872-at-anu.edu.au]
> Sent:   Monday, June 23, 1997 9:39 PM
> To:     tesla-at-pupman-dot-com
> Subject:        Building a new coil

I've stuck in several comments/suggestions to help you proceed with your
project--hope it helps and good luck with the whole thing.

Chuck Curran

> Hi all,
> I'm designing a new small TC for my neice to build for her high-school
> science project.
> I've done a few rough calculations, plus using a few rules of thumb, I've
> come up with this design -
> Secondary:
> ----------
> Sealed 4" diam PVC pipe, 22" long.
> 740 turns of 22 guage enamel coated copper wire closewound.
> Winding length of 20".

That's plenty long, consider a 16" wound length.

> (I take it that #22 wire is 0.67 millimetres thick?).
> Estimated self resonant frequency (unloaded): 317kHz.
> (Frequency should drop to a lower frequency with top toroid.

Well,  I get 521 Khz unloaded and 313 Khz loaded with a 13 pf toroid
(3x12)--no big deal, the rest of the key numbers in the primary look
pretty good!

>  BTW, does anyone know how to do a rough calc of a secondary res.
>  freq. with a known capacitance of a toroid and height above
>  top secondary turn?)
> Top Terminal: 12" x 3" toroid. (approx 12.95pF)
> Primary:
> --------
> 10 turns of 1/4" copper pipe.          _    _
> Spacing of 1/4" between windings ---> (_)--(_)
>                                          ^^
>                                           |----- 1/4" gap.
> Archimedes flat Pancake coil configuration, with first turn spaced at
> 1" from base of secondary.

Ah, do you mean a 6" diameter first primary turn, or the first primary
turn 1" below the secondary bottom turn?

> + Strike Rail (Probably not required, but a good idea).

I'd include it, easy to make and alot safer for the system.

> Width: 4.75"
> Average Radius: 5.375"
> Calculated Inductance: 30.33uH (at 10 turns)
> Capacitor Value: 0.01uF 20KVDC (Big cylindrical type, not poly, but
> hasn't failed me yet).

My calculations suggest a .01 Mfd cap too, with the 6" diameter first
turn on the primary, looks pretty durn good!

> Hence will require an approx. inductance of 25.2uH to resonate at 317kHz,
> so I'll probably tap somewhere between 9-10 turns.
> Mind you, that will decrease with the the added secondary capacitance.

Hold It--Increasing the secondary circuit capacitance will lower it's
resonant point.  This is typically done with a larger toroid. 
Therefore, with a fixed primary capacitance, in order to achieve system
tune, you would require MORE primary turns.

> Neon Transformer: 120KV 30mA Centre Tapped on secondary.
> Spark Gap: RQ Quenched static type gap with 10 gaps spaced at approx
> 1/8" each. Able to tap at any gap number desired (ie 1->10).

Another recommendation--use a .025" air gap between each of your
electrodes--you'll have real problems using 1/8" per gap, like it won't

> -----< end Specs >-----
> ...anyway, your comments and ideas are welcome...as always! :-)
> Thanks All!
> Catchya!
> Rod

Sounds like you got a good start to your project--now is this project
really "just" for your niece or are you going to have some fun too??

Chuck Curran