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*To*: tesla-at-pupman-dot-com*Subject*: Re: Mica Cap Question*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Thu, 17 May 2001 07:39:07 -0600*Resent-Date*: Thu, 17 May 2001 08:13:21 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <4XgwAB.A.JSB.mx9A7-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "John Crighton by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jcrighton-at-sia-dot-net.au> ----- Original Message ----- From: Tesla list <tesla-at-pupman-dot-com> To: <tesla-at-pupman-dot-com> Sent: Thursday, 17 May, 2001 10:34 AM Subject: Re: Mica Cap Question > 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) > > Hello Duncan, I am a learner so please humour me. Can you please go over part of your explanation above, as though you were addressing a dummy. >From this part onward I get lost: "hence the break rate will be near 12500bps ( = 1000 / 0,08 ) I am keen to learn and get a grip, but I do not understand about the spark gap breaks per second. Are you talking about a rotary gap or static gap? How does Voltage/joules give breaks per second? I am sorry if I am asking something that is common knowledge among coilers but I am a bit lost. If I do not ask, I will never know. Regards, John Crighton

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