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Re: Bipolar primary design

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

Hi Patrick,

First of all, even if you are running with a resonant Cp, if you keep your safety gap setting correct, everything will be OK (assuming static gap). Your BPS will be on the high side and if you want to lower it, you will need a larger Cp (1.5 to 1.6*Cres). If per chance no gap were to fire, the voltage could ring up to over 80KV (Q*Vs_oc).

The primary, I believe, doesnt know a whole lot about the secondary so your 12 turns should be close to correct to get resonance into the ball park. Analyzing the your 3.25x32 1/2 wave secondary as a 3.25x16 1/4 wave secondary is correct. Model the helical coil with half of it above the bottom turn of the secondary and the other half below the bottom turn (assuming you dont have any "dead" space between the two 1/4 wave portions of the secondary).

Alternatively, you could model your NST as a 6KV 60ma driving twice the Cp and half of the 12 turns and start the helical primary even with the bottom turn of the coil. This might model the proximetry effects the secondary has on the primary resonance better. I have never built one so if my thinking is wrong, someone will speak up :o))

Gerry R.

Original poster: <tesla@xxxxxxxxxxxxxxxxxx>

(I've posted about my bipolar coil plans once or twice on this list but I never seem to get the time to actuall start building the thing!)

I'm working on building a bipolar coil (the 1/2 wave, horizontal variety - NOT a twin). The secondary winding length is 3.25" x 32", wound with #28 wire, capped with a 3" x 14" toroid on either end. I'll be powering it from a 12/60 NST, with an MMC bank of 0.014 uF (this is right on resonance; I'm not worried about killing my NST as I have many of them). For the primary coil, I will be using a helical coil wound from 0.25" copper tubing, spaced at 0.20" per turn with a diameter of 9.75" (ie, 3 x the diameter of the secondary)

My understanding is that to analyse the properties of such a bipolar coil, I just need to "cut it in half" and analyse it as per a regular coil. In that case, I have a 3.25" x 16" secondary with a single toroid. Putting these values into WinTesla gives me a secondary freq. of 225 kHz, and indicates I'll need approx. 12 turns on my primary coil for tuning.....

ok, haha, all of that leads me into my one simple question....since I've cut everything "in half", does that include this primary? Do I need to double my primary, ie, use 24 turns for my REAL coil?

Thanks, all mighty TC list