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Registered Member #558
Joined: Thu Mar 01 2007, 10:28AM
Location:
Posts: 9
Is it possible to have decent spark using 32nF/16 kV capacitor with NST (12kV 20mA)...? Currently the spark is just few inches, maybe the coil is not tuned correctly. But before I start to put more effort on it, I would like to ask if it's even worth trying or schould I try to find smaller cap. According to my calculations optimal cap is 6.6nF so the one I got is far too big.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Getting the right cap size is important, as it affects the resonant frequency of the primary. If you calculated 6.6nf, but are using 32nf, switching to a smaller capacitor should help. Make 8 beer bottle capacitors, and you should be close to 6.6nf.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Too big a cap is a no-good thing. I'm thinking you probably want something around 8nF to be LTR for a 12/20 NST. So you're about 4x where you want to be!
A way-too-big cap probably means your NST can't charge it to full voltage fast enough. Your firing voltage will be reduced, requiring your gap to be tightened, and exponentially reducing performance. At the same time, to bring your coil into tune, you'll have to have far fewer turns on your primary, which together with the larger cap value, means your peak primary current will be much, much larger. So add higher I*I*R losses to the fact that a tigher gap with higher current is also generally harder to quench properly, and you can see why getting the cap value right is so important!
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
You definately want the capacitor to be the right value. Too small and the voltage soars too high, too large and your shorting out your transformer too much.
Registered Member #558
Joined: Thu Mar 01 2007, 10:28AM
Location:
Posts: 9
Thanks, that was exactily what I suspected I just needed a confirmation from experts. So in case of too big capacitor the NST don't have enough time to cherge fully, if I have understood correctly.
Registered Member #558
Joined: Thu Mar 01 2007, 10:28AM
Location:
Posts: 9
uzzors wrote ...
Getting the right cap size is important, as it affects the resonant frequency of the primary. If you calculated 6.6nf, but are using 32nf, switching to a smaller capacitor should help. Make 8 beer bottle capacitors, and you should be close to 6.6nf.
Bottle caps I made were a great success! Thanks for this hint. Now my teslacoil is able to make now sparks about 20 inch long. I guess that I can't make much longer sparks with 300W NST (12000V, 25ma)
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Too big capacitor?
