Re: arc-overs!

Subject:  Re: arc-overs!
  Date:   Fri, 18 Apr 1997 06:59:39 -0700
  From:  "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
    To:  "Tesla List" <tesla-at-pupman-dot-com>

Hi Chuck"

Your primary is much too close to the sec. coil.  We usually use 1 3/4
to 2 inch min.  You don't have to get it any closer because you usually
up elevating your sec. coil to acheive the proper coupling for max.
transfer.  Usually a 1 3/4 inch pri - sec spacing with the first turn of
the sec. coil starting 2 1/2 to 3 inches above a horizontal line even
the top of the primary elevation will work as a good starting point.  In
some systems you will find best coupling with sec. elevated 3 1/2 to 4
inches above this reference line.

Sounds like most of your problems are being caused by a severe case of

Hope this helps out.


> Good afternoon everyone,
> Here is a frustrating event I have a challenge with.
> While I was tuning my last coil design, and pushing the envelope a
> little a witnessed a nasty arc-over from the bottom of my secondary to
> the ground of my primary.  Here is the set up.
> Cp=75.7 nF
> Lp=45 uH, flat spiral
> Ls=125.7 mH, 113mm x 667mm
> static spark gap
> DC supply 15kV, operated variably using a 120V variac
> The system is designed to operate at 75 kHz.  My primary starts at 1/4"
> away from the secondary coil form, 
> 1/4" interwind spacing, 11.5 turns, 1/4" soft copper tubing.  The ground
> start nearest the secondary coil 
> form.  Since I operate at DC I have an actual ground for the power
> supply and a seperate RF ground to the same 
> AC mains ground.
> When I operated the system to its best, I had lifted the primary to
> roughly 1.5" away from the bottom of the 
> first winding on the secondary; in the hopes of improving the
> primary-secondary coupling.  This is where the 
> arc-over happened.  The arc started about 1.5 turns into the secondary
> and smacked into the ground connection 
> on the primary.  This persisted if I kept the voltage high enough.
> What surprises me is that there would even be enough potential 1.5 turns
> into the secondary to cause arcs to 
> ground on the primary.  This was a high current arc as well; very
> blue-green because of the copper vapor and 
> very thick and bright.
> What am I missing here?
> Chuck