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Re: Capacitor Help



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Malcolm,

I think you will find that threading the tubing thru the holes will be a pain. Many use HDPE material (white waxy looking plastic) for supports and drill the holes with the desired centers. Then they cut thru all the holes in a support a little off center so the final hole looks like a C. The tubing then just snaps into place. As you slowly uncoil the coiled tubing to match the curvature of the primary, you snap it into place and go on to the next one minimizing the unbending of the original coil. Since you are using wood, you could just deepen the slots so the tubing lays down into them. Once the tubing is in place, you could hot glue them so they stay down. More than 4 supports will also help keep the tubing where you want it and allow closer spacings. I use 8 supports others use 6. The larger the primary diameter, the more supports you will need.

Also to answer a previous question, LTR means larger than resonate. Often, one choses the Cp to be the largest value the NST can charge and still get a resonable BPS (average bangs or firings per second). For static gaps, this is often set at 1.6 * Cres and will yield around 120 BPS. Cres is the capacitance value that will resonate with the NST inductance at mains frequency (not good). For your 15KV 30ma NST, 1.6*Cres is about 8.5nf. It is also good to have more than 10 turns on the primary as this will reduce the peak current in the primary and be less stressful on the caps. I like to build 20 turn primaries using 1/4 inch copper tubing wound on 1/2 inch centers. I increase the top load to allow proper tuning to occur around the 17th turn. One should also check to make sure the top load toroid isn't so big that breakout doesn't occur. As the toroid increases in size, the breakout voltage goes up and the top load voltage that a given power source can generate goes down. Some like to have the top load as large as possible and still have it breakout (where the two curves cross). Some dont mine if breakout doesnt occur as they just add a sharp point to the toroid as a breakout point. This approach, however, directs the sparks all in one direction.

Lot of variables. Your first coil will be good to experiment with and learn about some of them.

Gerry R.



Original poster: "MalcolmTesla" <tesla@xxxxxxxxxxxxx>

I think I may also try 1 x 2 trim board turned on its side and drill some
holes towards the top.  Not just notches but actual holes so the copper
can't fly all over the place.  Then I'll slowly wind it in from the outside
towards the inside.