# Re: Mica Cap Question

```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
>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

```