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*To*: tesla-at-pupman-dot-com*Subject*: Re: Mica Cap Question*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Wed, 16 May 2001 18:34:09 -0600*Resent-Date*: Wed, 16 May 2001 18:48:06 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <G0MzX.A.o4C.C_xA7-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com> Hi Ray! >I have obtained a .01uF 8KV mica transmitting cap that is rated for 26 Amps >at 400KHz. Would make a good cap for a smaller MOT power coil? It certainly would, at least for short runs. The dc rating of your cap implies an rf voltage rating of just a shade over 1kV at the test frequency: At 400kc/s, a 0,01uF cap (= 1.10^-8 F) has reactance Xc = 1 / 2.pi.400000.1.10^-8 Xc = 40 ohms approx. 40 ohms x 26 amps ~ = 1kV rms for continuous duty. Alternatively, using the late Philip Kemp's way of reckoning for a spark transmitter circuit: An MOT is likely to be say 2kV -at- 1kVA, let's say 4kV with voltage doubler and with a 0,01uF cap this will give a bang size of a mere 80mJ (0,5 CV^2) - hence the break rate will be near 12500bps ( = 1000 / 0,08 ) If the break rate is 12500bps, the circuit resistance is 4 ohms (Terry has guessed this is close) and we assume the voltage is 4kV then I = E SQRT (n C / 2R) = 4000 SQRT (12500.1.10^-8 / 2.4) I = 4000 SQRT (1,56.10^-5) = 15,8A which is within ratings. [ in the above, I is current, E applied voltage, n the breaks per second, C capacitance, R resistance ] Note that two MOTs would put that current well over the rated value. I think your cap will do fine for short runs, I'd be a little worried if you wanted to run two MOTs for extended periods. Dunckx Geek#1113 (G-1)

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