Re: sparks running down secondary - why?

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

Original poster: "Kennan C Herrick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kcha1-at-juno-dot-com>


On Mon, 28 May 2001 14:09:47 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Bill Vanyo by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <vanyo-at-echoes-dot-net>
> 
> Last time I ran my coil, I got occasional loud snappy sparks 
> running
> down the length of the secondary, as well as occasional firing of 
> my
> safety gap.  Wondering what causes the sparks down the secondary, 
> and if
> it's a problem?

I saw this just the other day when I had moved my coil (a s.s. one; see  
http://hot-streamer-dot-com/temp/Tcg1.jpg and also -tcg2.jpg) from its usual
location just above a concrete slab to a wood deck upstairs (for a big
party).  I'd put down a 4 ft-square wire mesh, tied to a ground rod, as a
counterpoise but it seemed it was not quite enough: I got the occasional
spark running from a MOSFET heat-sink to just about the center of the
secondary.  Happily, no damage either to the MOSFETs or to the secondary.

I suspect that, as soon as the spark formed from the toroid, that
"anchored" the potential of the toroid with respect to earth ground. 
Then, the ac potential of my entire primary apparatus moved far enough in
the opposite polarity to so as to cause the breakdown--right to the
center of the coil, which would then have been at virtual ground
potential.  That's probably what's happening with yours.

Ken Herrick
Oakland, CA
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