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Re: Suicidal Secondary--Update



Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 1/11/02 7:47:35 AM Pacific Standard Time, tesla-at-pupman-dot-com
writes: 


>
> > 
>
>    Hi everyone. 
> First I should thank all who gave suggestions.  I just got around to 
> running the coil tonight, and had a chance to put a few of your ideas to 
> work.  I patched the craters from last week's run with 5 min. epoxy, put 
> plexiglass washers around the top half of the coil, and rested a 3" dia. 
> toroid on the top washer as an anti-corona ring. 
>
> These worked to some extent, but not as well as I hoped.  I got no full 
> secondary arcs, but had many hot racing arcs trying to find a way around 
> the washers.  There were also arcs running in between the washers.  I 
> did the coupling calcs. that Terry suggested, and found that the highest 
> coupling I achieved was 0.12.  It sure looks like I'm overdriving the 
> heck out of the coil, but I'm only running at 1.5kVA.  The bang size is 
> about 5 joules.  I tried both toploads (6" by 20" and 8" by 22" 
> toroids), with the coil tolerating the smaller one best, but with much 
> decrease in spark length.  My big topload gave the coil trouble, but 
> cranked out 4 1/2 ft. sparks (at the most).  This run was done in moist 
> air, when the racing arcs are less of a problem.  Running the coil on a 
> dry day would probably be a disaster. 
>
> I'm sorry if I'm being a nuisance, but I am really at a loss here.   I 
> can't see how many of you are able to crank 4 and 5 kVA into a 6 inch 
> coil similar to mine (achieving sickeningly large sparks in the process 
> :-))  What did I do wrong? 


-- snip -- 

Winston, 

In my opinion, racing sparks on the secondary are caused by either running the
coil out of tune, overcoupling or just overpowering the coil - putting in more
power than it can take.  I use two toroids on both of my coils, one right on
top of the secondary (to prevent sparks from leaving from the top windings)
then another raised up on a hollow cylinder made out of aluminum sheeting.  The
upper toroid is larger and most of the discharges will leave from the here and
go up and out, preventing strikes down into the primary.  My 6" coil produces
sparks that are more than three times it's winding length. 

Have you done the math on this coil so you know approximately where it should
be tapped on the primary?  Is the best tune point within a turn or so from
there?  If so, I would suggest that you are overcoupled.  Is your primary
flat?  A normal flat primary usually provides acceptable coupling with the
first secondary turn set to be even with the top plane of the primary.  Lay a
ruler on the primary and it should be just even with the first secondary
winding.  If you have an inclined or saucer shaped primary, the secondary will
need to be raised up possibly an inch or more to prevent overcoupling. 

Ed Sonderman