Re: Fiberglass Coil form

To: tesla-at-pupman-dot-com
Subject: Re: Fiberglass Coil form
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Date: Thu, 21 Nov 1996 06:58:23 -0800
Tesla List wrote:
> 
> >From storey-at-stic-dot-netWed Nov 20 22:15:34 1996
> Date: Wed, 20 Nov 1996 11:28:33 -0600
> From: Storey Clamp <storey-at-stic-dot-net>
> To: Tesla-at-pupman-dot-com
> Subject: Fiberglass Coil form
> 
> Hi,
>         I was wandering through my favorite junk yard and came across a piece
> of fiberglass pipe, 10" diameter by 7 feet long, clean, apparently
> unused. I asked the junk dealer and he said,"It musta come in on some
> truck, but its nothing I can sell, so you can have it if you want it".
> So now I have a beautiful, light weight, 1/8" wall, coil form, and I am
> iching to start winding. I have on hand a supply of 22gauge formvar
> which would give me a winding length of 27 inches for 1000 turns, or
> should I go out and buy some 18 gauge and wind 40 inches for 1000 turns?
> I would like to optimize for maximum spark. Any comments from the
> experienced coilers would be appreciated. Thanks,
> 
> Storey Clamp
> San Antonio, Texas

Storey,

Nice score - and long enough to build 2 resonators! I've assumed 10" OD
in the estimates below. Some comparisons of the two proposals uloaded
(less toroid) and with a fair-sized (30" diameter) toroid of, say, 25
pF.
The winding "closeness" factor takes into consideration that you
generally won't be able to wind the secondary "perfectly" - there will
be small/random fluctuations in wire-to-wire spacing, which have the
effect of reducing the number of turns for a given wire length. 

22 AWG, 27", 97% "winding closeness":  
   969 Turns
   75000 uH 
   Fo~150 kHz (unloaded)
   Zo~71 kOhms kHz (unloaded)
   Fo~92 kHz
   Zo~43 kOhms

18 AWG, 40", 97% "winding closeness":  
   916 Turns
   47466 uH
   Fo~180 kHz (unloaded)
   Zo~54 kOhms (unloaded)
   Fo~113 kHz
   Zo~34 kOhms

Either should work fine!

However, I'd tend toward the bottom coil or use a wire size in between -
say 20 AWG.  The maximum output voltage withstand capability of the
secondary is a function of coil height. Also, we'll reduce streamers
from the toroid to the primary strike rail by using 18 or 20 gauge on
longer length forms. The top coil may be too short if you eventually
plan to drive the system to higher power levels. 

Safe coilin' to ya!

-- Bert --