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FW: which disease?


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From:  Barton B. Anderson [SMTP:mopar-at-mn.uswest-dot-net]
Sent:  Thursday, March 19, 1998 1:51 AM
To:  Tesla List
Subject:  Re: which disease?

Arwin,
I'm new to coiling, but thought I would give this a shot anyway -

Tesla List wrote:

> ----------
> From:  solva-wijnschenk [SMTP:solva-at-xs4all.nl]
> Sent:  Wednesday, March 18, 1998 6:20 PM
> To:  bert pool; DR.RESONANCE-at-next-wave-dot-net; john freau; richard hull; tesla-at-pupman-dot-com
> Subject:  which disease?
>
> Dear All, I need some help.
>
> I wound a coil (diam. 4.33", height 33.66") with .35mm wire (AWG 28??)
> and a total secundary resistance of approx. 155 ohm. I thought that
> these 790 meters from 2290 turns would give me resonance at 94,8 kHz.
> Why not???

With these dimensions I calculate your Ls at 69mH and Cself at 12pF,
   therefore, 1/2pi(sqrtLC) = 175kHz (no top load).


> Everybody talks about 3:1 ratio but that means with 10" diam
> ->30"height, doesn't it.

No, you don't need a longer coil. The length of the wire determines the frequency. With a
wider secondary, you will increase the length per turn and thus less turns are required to
acheive the same length. Therefore, the coil height can be shorter.

> How do I get 1000 turns in so little height.
> Can I take a form with more height??

Using your 3:1 example of 10"w and 30"h,Circumference = 31.42" (per turn). That's a lot of
wire. If you used #24awg at about 40turns/inch, you would end up with about 1200 turns,
ratio of 3:1, Ls of 104.3mH,
Cself of 15.5pF, and an unloaded frequency of 125kHz. A 10pF topload should get
you back to the 95kHz range (if you wanted).


> I now get breakouts (>20") at half of the form, distroying my turns.

Ouch. Sound's like you've wound the secondary to 1/2 wavelength of the tank resonant
frequency putting your highest acheivable Vs at the center of the windings. I calculated
175kHz and your tank frequency is 95KHz? Almost half isn't it.

> I am using a cap wound from 2.5mm thick red plastic (don't know the
> material) 2 plates from about 20 cm widht and 7 meters long. Primary is
> 7.5 turns of .5" copper tube, gap=single .5", toroids vary. Best
> sparklength I get (don't understand!!!) with a very small toroid! Supply
> is a 10 kv 10kva plate transformer and a variac.
>
> is it wise to build a new coil with 8"diam and what height and number of
> turns should it have??? What wirediam??? I am thinking of using wire
> used in mainssupply (2.5 mm2). at least is low resistance. What am I
> doing wrong?
>

First, I think you have miscalculated your secondary resonant frequency. If I were you, I
would go back and recalculate the circuit again and consider somewhere between 3:1 - 5:1
secondary geometric ratios. Based on your transformer, you could probably use 18 to 20 awg
wire size with no problems.

> Please advice and thanks,
>
> ARWIN, Holland

  Bart