Re: Latest coil

To: tesla-at-pupman-dot-com
Subject: Re: Latest coil
From: Bert Hickman <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 08 Sep 1999 11:58:04 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme
Gary, Don, and all,

I suspect that you're seing the effects of overvolting the secondary
coil. This often occurs when the coil length is too short for the peak
secondary voltage that's being developed, or the insulation of the
secondary wire is poor. Racing sparks tend to be faily random, seem to
be confined mostly to the upper portion of the coil, and can be
relatively easily eliminated by reducing the primary to secondary
coupling. On the other hand, overvolting is often not corrected by
reducing the coupling, and is characterized by discharges from the top
to the bottom (or near bottom) of the secondary. Overvolting can be
brought on by any change which will tend to significantly increase the
peak secondary voltage prior to breakout. This can include increasing
the gap size, tank capacitor size, or the toroid's minor diameter.
Getting streamers that are greater than 2.5-3X the secondary coil length
requires careful construction of the secondary and good electrostatic
field control by the toroid.

The fix is simple - use a longer secondary winding, wound from
double-insulated magnet wire or plastic insulated wire. A heavy topcoat
of a relatively high-k 2-part resin coating such as Behr Build 50 or
Aristocrat Coating will also improve the dielectric strength of
a secondary wound from magnet wire by helping to "smooth" and reduce
point stresses in the e-field around the top of the winding. These, or
equivalent products, are typically available at Home Depot of craft
stores. The latter product is also available through Craftswholesale on
the web at http://www.craftswholesale-dot-com/ under "Aristocrat Epoxy".

Safe coiling to you!

-- Bert --

Tesla List wrote:
> 
> Original Poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
> 
> The racing sparks occurred for as long as I ran it, which wasn't too long
> since I was afraid I'd damage the secondary (and did).  My secondary is
> 4.25" dia x 23" long.  I think I may follow the advice offered by John Freau
> and build a larger (6 x 28) secondary.  In addition to being longer, this
> will also allow me to use more primary turns with a higher surge impedance,
> and lowering the frequency is good in that it lowers losses.
> 
> For both of us, the racing sparks began when we used higher valued caps,
> which not coincidentally required us to use fewer primary turns.  This had
> two unintended consequences.  The coupling is increased with fewer turns,
> and the transformer turns-ratio is increased.  I hope that a larger
> secondary, leading to more primary turns, will fix this.
> 
> Regards, Gary Lau
> Waltham, MA USA
> 
> >Original Poster: Don Allen <dona-at-amigo-dot-net>
> >At 01:00 PM 09/05/1999 -0600, Tesla List wrote:
> >
> >Hi Gary, all,
> >
> >I've been using just one .01 mfd cap on my coil for a while
> >doing experiments. I added the second one into the circuit
> >last night to get .02 mfd and got racing sparks right off the bat.
> >Actually, the sparks want to travel straight down to the base
> >of the secondary.
> >
> >Since I last ran both of the caps together, I have adjusted the
> >secondary coupling. It is fine with one cap but with both I think
> >it's just too much. With two caps, there's a lot more corona
> >coming off the topload
> >
> >Do the racing sparks happen the entire run, or do you
> >notice it at a few seconds into power-up? Mine were the
> >entire (brief) run.
> >
> >Don