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Re: Combining several caps



Original poster: "Ramon van der Hilst by way of Terry Fritz <teslalist-at-qwest-dot-net>" <enqrypzion-at-yahoo-dot-com>


Today we've measured the NST, and the secundary RMS voltage is 5640, giving 
a peak voltage of about 8,5 kV. (<I've learned! :D) Actually quite strange 
numbers, as it's not near the 2x4000 it said, yet the peak is higher.. 
might this've happened because we measured at an input of 2 VAC, giving an 
output of 54,8 VAC?

well anyway, after taking a better look at some sites about MMC's, I've 
been searching around for some polypropylene MKP caps. On a postordersite, 
<http://www.conrad-dot-com>www.conrad-dot-com I found Epcos MKP polypropylene caps 
with the following specs:

  0,15 µF, UN = 630 V=, Ueff = 250 V~, tolerance 5% and 6,0 x 15,0 x 26,5 
mm (width x height x diameter).

I was thinking about buying 50, 10 extra, and using 40 of them. That would 
give (I've learned again ;-) tnx all!)  0,00375 uF -at- 10 kV, while wintesla 
and tcc both gave 0,0037 uF as needed capacitance (for 5640V, that is RMS).

I was wondering though, as neither of the programs mentioned it, whether 
you have to fill in the RMS values or the peak values. anyway, are the caps 
right? (if it's peak voltages then we'll adjust the amount of caps to the 
right capacitance... as long as it's still 9kV or more).

tnx again!



  Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Sean Taylor by way of Terry Fritz "

 > We've acquired a NST (sec. : 8kV, 10mA at 220V, 50Hz) and so WinTesla
 > suggested we use a 4 nF capacitator.

 > What seemed the simplest for us is using 16 (C1) 1nF 2kV caps, placed in 4
 > parallel rows of 4 caps in series.

SNIP . . .

Well, there are a couple problems here. First, the 4 caps in series will
total up to exactly 8 kV, where your NST is an 8 kV NST, and will actually
put out 11.2 kV on the peaks, plus the ringing in the primary tank circuit
will repeatedly reach a high voltage as well. You'll need a cap rated for
at least 12 kV. Second, 4 caps in series, while increasing the voltage
capability, will decrease the capacitance. Four of your caps in series will
be 0.25 nF at 8 kV, so 4 strings of 4 will yield 1 nF a! t 8 kV. You're best
bet for a cap right now would probably be a saltwater cap, easy to make,
cheap, and variable size. Someone recently posted the Geek Group bucket cap
link, or you can search for it on google. Good luck!

Sean Taylor