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Secondary with thin wire


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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Thursday, February 19, 1998 12:29 AM
To:  Tesla List
Subject:  Re: Secondary with thin wire

Tesla List wrote:
> 
> ----------
> From:  Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent:  Tuesday, February 17, 1998 1:47 AM
> To:  Tesla List
> Subject:  Secondary with thin wire
> 
> Hi:
> 
> I was looking what I have around to build a small capacitor-discharge
> Tesla coil. I found a PVC tube with 8.8 cm (3.5") of diameter (more
> than enough, about 2m) and many spools of 32 AWG magnet wire (relay
> coils). By my initial calculations, I think that I can build an
> acceptable secondary with this rather thin wire, with 1500 turns, what
> results in a winding measuring 30 cm (I don't want sparks longer than
> about this for awhile).
> The inductance would be 20.8 mH, the self-capacitance 10.4 pF,
> with resonance without top terminal at 305 kHz. Considering only the
> DC resistance of the wire (223 Ohms), the Q reaches 435 (I didn't
> compute the skin effect and other losses yet). I will have to use
> five of the spools to complete the required wire length.
> Some advice on how to make this work? Is the thin wire a so serious
> problem? An it is really necessary to dry and coat the PVC tube with
> polyurethane varnish before the winding? (saves a day).
> 
> Thanks,
> 
> Antonio Carlos M. de Queiroz
> mailto:acmq-at-compuland-dot-com.br
> http://www.coe.ufrj.br/~acmq

Antonio,

For a small coil, the fine wire should work quite well! The only problem
I'd have is trying to see the blasted stuff to close-wind it! I'd still
coat the tube, since it will otherwise be a source of additional loss
that's easily preventable at this stage. 

A 3.5" diameter winding about 1 foot long (~30 cm) close-wound with #32
AWG (97% winding density), should result in about 1300 turns, and about
39 uH of inductance. The Medhurst self-C would be about 5.9 pF, and a
self-resonant frequency in the region of 340 kHz with no top-load. A 3"
x 12" topload would drop this down to around 180-200 kHz. Should work
like a charm!

-- Bert --