Hi David,I think John's latest is 1.7*sqrt(input watts). I think it started out at something like 1.42 as the factor? John's done a number of tests since then including bps testing and he posted some variations to the equation. I think the 1.7 factor has been out there a while now as the number to shoot for but may be hard to achieve depending on losses. In Javatc I also show John's value but I incorporate a k factor depending on secondary diameter from which I got from Dr. R. For coils less than 10" diameter, I'll multiply by 0.85 as an efficiency factor.
John also tested the above at 120bps. In John's testing, he lost some spark length with increased bps. However, that can be true in cases but not true in all cases. Depends a little on several factors. Actually, I worked this equation out several years ago. A lot more could be looked into, but the gap efficiency will vary for each coil which makes going any further a mindless ordeal.
Don't be surprised I'm running an NST in STR mode. I still believe LTR is safer for NST's, but it also means more dollars! I'm no different than anyone else (I get away with what I can when I can). But also note I lowered the NST voltage. Remember the static gap is self limiting as based on the gap width and it's own ability. So the voltage is clamped by the static gap and the Terry filter (with safety gap) also provides needed protection. BTW, this is that same coil I've ran for 30 minutes non-stopped. There is no resonant rise as I'm far off to the left of resonance. Now if I had a gap problem (stopped firing for whatever reason), that's when things could turn ballistic (but that's why we have safety gaps). Without the safety gap and with a main gap that stopped firing, the NST would certainly pop!
Take care, Bart David Rieben wrote:
Bart, Ok, it doesn't affect the spark length as much as I thought it would, though. I didn't realize that the math worked out like this either. I was just assuming that the spark length was a simpleresult of the sqrt(power) x 1.2 and the power was simply a factor of the bps x C, in joules. Iguess that's what I get for assuming ;^) Also, I am a little surprised that you are actually running an NST coil STR, considering the prevailing school of thought about LTR operation for the fragile NSTs in the last decade. Spark on, David Rieben
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