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Re: [TCML] Need assistance in diagnosing poor performance

Stephen -
   
  It looks like you bought the $900 "Tesla coil kit" from eBay seller rainylk, consisting of a 12/30 NST, a pre-wound 4" X 22" #22 AWG secondary, a 3" X 12" spun toroid, CD 942 series film/foil caps, parts for a Terry filter, a single-segment tungsten-rod spark gap, and various other pieces. See eBay item # 130239387220 for the details of all the components. You are correct in that this kit, when properly assembled and tuned, should yield better than 3" streamers. This coil should easily generate 2' streamers, and with some optimization (including parts NOT provided in the kit) should do significantly better than 2'.
   
  If your coil is only generating 3" streamers, something is VERY wrong.  Here are some suggestions for a methodical approach to determine exactly is wrong:
   
  1. Verify all component values are correct, especially the resistors and MOVs used in the Terry filter, and the capacitors and bleeder resistors used in the MMC.
   
  2. Verify the wiring is correct, and all connections are tight and low resistance, especially in the tank circuit.
   
  3. Verify that both sides of the NST are generating full voltage (carefully check arc length to the NST case from each bushing).
   
  4. Verify the connection from the top secondary winding to the toroid is secure.
   
  5. Tape a small fluorescent lamp to the top of the toroid so end end extends well off the toroid, and use this as an indicator of topload voltage less than that required to obtain breakout.
   
  6. Temporarily set aside the electronic "tuner" and, starting at the outermost primary turn, start tapping and testing, moving inward in 1/4-turn increments until you start to get some output.
   
  7. If the coil is properly designed and correctly assembled, somewhere between the outermost and innermost primary turn you will find resonance. Remove the fluorescent tube, and start "fine-tuning" the tap point to obtain maximum output. If you don't achieve 2' streamers by this time, post a whole series of clear photos of every component part of the coil, and all the interconnects, for TCML members to review.
   
  8. 98% of the time,  "poor output" from a first coil is due to it being out-of-tune. As you bought a pre-engineered "kit", I assume that you personally did not verify the design parameters for the primary, secondary, tank capacitor, and topload, and are relying on the seller to have designed a coil that can be brought into resonance with the parts provided in the kit. It might be enlightening, and well worth your time, to spend an hour using one of the better Tesla coil design software packages to verify all the dimensions and parameters of the parts in your kit, and verify that the design is valid and the parts you received are capable of being brought into tune.
   
  Personally, after getting the coil operating satisfactorily, one of the first things I would do would be to go to a simple multi-segment spark gap instead of the single-segment gap. In my early coiling days (after tuning to achieve achieving resonance) the biggest single performance improvement came from changing from a single-segment spark gap to a fan-cooled multi-segment gap.
   
  Regards,
  Herr zapp
   
   
   
  

"Stephen J. Hobley" <shobley@xxxxxxxxxx> wrote:
  We're still not getting the performance we would expect out of the Tesla
coil we built.

It might have been the humidity that killed it tonight, as performance
was the worst yet - spark length was only 3" using the safety wand.

Where should I start in looking for problems? I've built the 555 timer
based tuner and re-tapped the primary at coil 11, as this gave the
dimmest indication, as per the instructions.

Apart from that, I'm a bit stumped. 

I've seen evidence that this coil can give much better performance -
Alan sent me some recent pictures of a US military coiler over in Iraq,
getting at least 25" arcs out of his coil - exact same specs.

Maybe the desert air helps...

Any help is greatly appreciated.

Steve
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