Ooops Short height limit for toroids.

["Tesla list" <tesla@xxxxxxxxxx>]

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.