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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.