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Ooops Short height limit for toroids.
Original poster: "Garry Freemyer" <garryfre@xxxxxxxxxxx>
About a couple years ago, I had purchased a Tesla
coil off of a coiler on the list from EBay and it
came to me completely mis-wired. Both HV wires
went to ONE end of the NST, loose connections and
a few other mis-wirings. I fixed it and wrote the
fellow mentioning the problem and they were as
puzzled as I was about how it happened to get
that way because they had tested it out before
shipping it. The secondary was a five and a half
inch outside diameter pvc capped on both ends and
each cap was covered in foil but there was no way
to be sure which end was ?Up?.
I never ran it much but have been in the process
of getting things sold, thrown away and all
because I?ve been unable to find programming work
and am preparing for the worst.
I dug out the Tesla coil and noticed two burn
marks on the secondary as if there were arching
across the windings that were covered with
silicone seal. I know I did not do this, I would
have remembered it knowing the horror I would
feel as I watch a good secondary go bad. I
started it and immediately the burn marks started smoking badly.
I took the windings off and discarded the AWG 24
wire and as expected found and removed metal
fragments from the pvc pipe. Winding length was
17? exactly and decided to recalculate the length
I would need to maintain the same resonance by
using the formula 24/28 * 17 = the new length
which turned out to be about 11 and a half
inches. I had tried a few java calculators on the
net, but the results did not agree, in fact, the
same java calculator gave a winding count of 40
and 44.4 per inch given the SAME parameters!
I rewound the coil figuring that I could simply
have the toroid five and a half inches above, at it?s original height.
Instead of the streamers emitting from the
toroid, they emitted from the top winding to
strike the primary. Definitely no the result I wanted.
I soldered, the end and wound the coil to 17
inches, hoping I could adjust the primary that
was wound with copper tubing, to work. I only
needed to buy about three feet more of smaller
pipe to get it reasonably in tune.
I consider myself darn lucky that it worked but I did learn a few things ?
* The maximum working height of a top load in
relation to the secondary is a LOT smaller than I
figured. I wonder if there is a formula to figure it out.
* Always closely inspect any coil you
purchase for burn out and other defects. I find
the folks on the Tesla list are a very nice bunch
of folks, but we are human, and it is easy for
anyone in the business of making coils to forget
to test a coil, or grab a defective secondary
when they intend to send a good quality unit.
Mistakes like this are easy for any honest person
to make besides, it feels better to think it was
an ?Honest? mistake, than the alternative. J
* If you can?t adjust the secondary, or the
capacitance or the NST, don?t forget, there is
such a thing as adding windings or multiple
levels to the primary winding! <Evil Grin!>
* Floors attract epoxy covered secondaries
like magnets, and will yank them from your hands when you least expect it.
* Brush on clear coat casting epoxy covers a
multitude of sins, er soldered splices.