On 7/27/16 9:46 AM, undisclosed recipient via Tesla wrote:
12kV. 90 mA. Tuned to 187 kHz with 29 nF primary cap and 200 uF PFC cap. The toroid is 20.5" sitting on top of 1182 turns of 26 ga on a 4" ABS core. Per javatc, I should be pulling 48" arcs, but I can only manage around 28 - 30". I was told I need more capacitance... However they did not explain their view. I currently have 17 0.5 uF 2100 vac caps in series. I can only think they mean I need to double the string to 34 caps and then make a twin string and connect in parallel, for a total of 128 caps total.
what kind of capacitors are those? What's your primary inductance? How long is your secondary winding? (the total length of the winding part)To a certain extent, the spark length is determined by the stored energy in the primary capacitor.
with 12kV, 90mA that's about a kilowatt.. you get 120 or 100 bangs/second, so each bang should be around 10 Joules.
energy = 1/2 CV^2 so 10 = 0.5 * C * (12)^2C = 10/(144*.5) = 0.138 uF -> this would be what's called the "resonant" size and is actually a dangerous size to use (if you miss a bang, the voltage will rise and ruin your NST).
But in any case, with 29 nF, you're getting about 2 Joules/bang. You might be getting multiple bangs/half cycle, since you'll fully charge before the half cycle is over, you'll get a bang, and then recharge again.
You can probably tell from the sound of your coil when it's running. If you're getting the optimum 1 bang/half cycle, you'll hear 2xline frequency, which is pretty low pitched. if you're hearing something more like middle C (256 Hz), you're getting multiple bangs/half cycle.
Doubling your C wouldn't be a bad strategy: you'll double the bang energy while still staying well under the resonant point.
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