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You might also try reducing the number of plates used on your tank cap since a 15/30 NST will optimally drive a tank cap that's about 8 - 12 nF when used with a static spark gap. When the tank cap is too large for the NST, the NST doesn't have sufficient current to charge the tank cap up to the point where the spark gap will fire on every half cycle of the incoming AC waveform. Try not to reduce the capacitance to less than about 8 nF. Using at least 8 nF reduces the possibility of accidentally overvolting your NST (from 60 Hz resonance effects between the NST and your tank cap). The other possibility is that your tank cap may have developed a high voltage short. If this is the case, the cap will measure OK at low voltages, but will internally arc over when high voltage is applied. This will also prevent the spark gap from firing. Is your tank cap oil immersed? Oil immersion is essential to keep corona from damaging (and rapidly destroying) the polymer dielectric, particularly at the foil edges. Again, good luck! Bert
: Hey,
:
: We have recently built a high voltage Tesla coil for a graduating project
: for our high school, but we're having some problems. My friends and I were
: hoping that anyone might be able to help us troubleshoot.
: Our coil itself is powered by a 15kV 30mA neon sign transformer. The
: primary coil has 11 turns of 3/8 inch copper tubing, with an inner radius
: of 3.5 inches and an outer radius of 13 inches. The secondary is 26 inches
: tall with 22 gauge copper wire. We have a static spark gap and safety gap
: that are easily adjustable. We built the capacitor ourselves out of
: polyethylene sheets and aluminum. We believe it to work well and have
: found it to be 18nF.
: The problem is that once the coil is wired the transformer fails to fire.
: There is no arcing across the spark gap, and no noise indicating that the
: transformer is working. Our schematic has the spark gap and safety gap in
: parallel with the transformer and in series with the capacitor and primary
: coil.
: We feel as though we're missing something simple. The components
: themselves seem to be working properly but when wired correctly the coil
: does nothing. We have found it possible to create arcing in the spark gap
: but only when all the components are wired in series. When this happens,
: however, we can tell that the primary coil creates no field because we
: have held a fluorescent bulb near it with no result.
: Any help would be greatly appreciated. Hopefully you have a chance to
: respond soon as we do have some time constraints.
:
: Sincerely,
: Ian, Thomas, Chong
:
:
Hi Ian,
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