Re: safety gap / terry filter question

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Larry,

At 05:12 AM 10/16/2002 +0000, you wrote:
>just installed geek caps.  noticed the safety gaps firing more than usual.
>first slowly, then more frequent. then a few loud(er) cracks.
>after realizing that the terry filter (that is 'folded') is arcing between 
>nst hot 1 and nst hot 2,
>I readjusted the PE tubing insulation.  it helped but I need to think of 
>another fix or a redesign.

The Geek caps may make things more efficient or the tuning is a little better.

>
>BUT I ramble.  the safety gap fires occasionally and then increases.
>THEN it arcs between the hot legs of the output.  about 1.25" or so.  this 
>is the
>unfiltered side.  what would be causing this?

1.25 inches is pretty far.  Are there any sharp edges or surface for the
arc to travel along?  If so, dull the edges or slit the surface.

>
>ALSO I'm currently testing a helical primary on the coil. so my coupling is 
>probably like .2 or .3.
>coil specs... 12kv/60ma. sucker gap. 12.5nf cap. 4.5inch sec (22awg, 36inch 
>winding length)
>primary is 8 or 9 turns on 7" sono tube with 1/2" spacing using 12gauge 
>stranded.
>no racing. as sonotube to secondary spacing is like 2inches. AND i have like 
>5 coats of poly on it.
>if it carbon tracks, I have like 7 miles of wire anyway. it just sounded 
>(helical primary) like something
>fun to try.

With a 12/60 NST and a 12.5 nF cap you can resonate the primary circuit to
excessive voltages.  I worry that may be causing the very long arc overs in
the filter.  Be sure the safety gaps are set right and avoid the temptation
to open them further.

>
>why arcing between legs of safety gap?
>1) too darn close, duh!
>2) high freq likes to travel on surfaces.
>3) unknown effect from high coupling ?

See the above and worry about too much voltage.

>
>terry filter questions.
>when movs fail, they fail closed? (as in 0 resistance)

As they heat and the solder inside them melts, their voltage will drop way
low.  They usually get very hot and smoke.

>will arcing between legs of filter (after the movs, caps, bleeders, but 
>before power resistors) damage or stress filter?

If the voltage is too high the MOVs may be damaged but with things arcing
like you say, it sounds like they are fine.

>will arcing between safety gaps damage or stress filter? (between high sides 
>of output, not as in to ground in overvoltage protection mode)

As long as the safety gaps don't melt down it is fine.  The safety gaps
firing too much may indicate that the voltage setting for the main gap is
too high.

Cheers,

	Terry

>
>
>any tips?
>larry.
>
>