Re: the cure for racing sparks

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steven Ward by way of Terry Fritz <twftesla-at-qwest-dot-net>" <srward16-at-hotmail-dot-com>

Hi Paul,

Well everything that you mention is quite true, but ive managed to 
overcome(i think) these problems.  Ive tried all sorts of toroids, but they 
are not as good, and throw several smaller sparks.  The sphere almost always 
breaks from the upper side or top of the shpere, not usually at the 
bottom(since it is flat).  And ive tried the sphere on top of the toroid, 
but the sparks werent nearly as good, and again, it made several weaker 
sparks.  I feel that the sphere does very well with a small nut on top,  it 
has no trouble breaking out there, and its never shot down the secondary 
with the breakout.  I just like the violence of the coil when there isnt a 
breakout point.  Its much more entertaining to me, you never know what will 
happen!!  And in this way, it seems like the arc are louder, and sometimes 
attract to nearby people (out of reach of course, but close enough to feel a 
charging on your face!!!  its really amazing!!).  I think that my coil is 
doing fine now, my rebuilt transformer seems really robust, in that it takes 
lots of abuse, especially with the kickback from the sphere.

Steve Ward
PS, thanks a lot for all of the help with my VTTC, its slowly becoming more 
reliable, and i understand my problems now.



>As regards the sphere, any topload will tend to break out from the
>point on its surface which has the highest field strength.  In the
>case of an isolated sphere, this could be anywhere.  But put it
>atop a secondary coil and the highest field strength could well
>be just where you don't want it - where the secondary meets it!
>A sphere just doesn't do a good job of directing the breakout to a
>desirable place.
>
>One advantage of a toroid is that the highest field strength occurs
>at the outer rim, and the area where the top of the secondary meets
>it is a fairly quiet backwater as far as the field strength is
>concerned.  Another advantage is that, for a given breakout
>threshold voltage, a toroid will hold more charge than an
>equivalent sphere, so that when it does break out, it will send
>out a longer streamer.  Toroids are rather nice for this job, you
>have two degrees of freedom in the design - thickness and diameter.
>Roughly speaking, choosing a thickness sets the breakout voltage
>(by setting the minimum radius of curvature), and choosing a width
>determines the charge available for streamer formation (by setting
>the capacitance).
>
>Steven Ward wrote:
>
> > It takes a few seconds, then WHAMMM!!! a
> > huge 28" arc will jump out into the air.
>
>Your existing radius of curvature (6") seems quite large compared
>to that of toroids typically used with this size and power of coil
>(say 4-6" thickness = 2"-3" ROC?).  Therefore your secondary is
>doing a pretty good job of containing the voltage applied to it in
>the presence of an unhelpful topload.  So I'd recommend switching
>to a toroid.  This way you can reduce the peak voltage reached by
>the system, and at the same time maintain or increase the available
>charge.  You might well find that for best operation, the primary
>ends up being tuned 5-10% below the secondary Fres.
>
> > i use a sphere (12" diameter) because its the coolest damn
> > thing ive ever used for a topload!
>
>Hmm, sit the sphere on top of the toroid?
>
>[*]
>  http://personal.inet.fi/atk/dncmrc/thor.htm
>--
>Paul Nicholson,
>Manchester, UK.
>--