# Re: Cap question.

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> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: RE: Cap question.
> Date: Friday, October 06, 2000 4:14 PM
>
> Original poster: "Garry Freemyer" <Garry-at-NDFC-dot-com>
>
> I remember reading this in a book someone showed me that basically said
take
> two caps, one of say .1 mf and another of .01 and put them in series with
> 100 volts. If I remember, the voltage drop accross the caps will be 90
volts
> accross the smaller cap, and only 10 volts accross the larger cap.
>
> Electricity sure is an odd thing. Its a good thing you said this because
I
> was about to do the same thing. I guess I don't understand how the
voltage
> would behave like this.

It's because the impedance of the capacitor is 1/(j *omega*C) where j =
sqrt(-1) and omega = 2*pi*frequency (yep, odd things, but in the long run,
it makes things easier)...  If you work in terms of reactance, X = 1/(2 *pi
* freq * C)..

Reactances/Impedances/Resistances all follow Ohm's law.. E = I * Z.. if
your circuit is all reactive (i.e. X) or all resistive (i.e. R) then it
simplifies to E= I * X or E = I*R. If there is a combination of the two it
gets a bit hairy-er...

Anyway, consider your two capacitors... Because C is on the bottom of the
fraction for X (or Z) smaller C means bigger X.  Bigger X means bigger
voltage (= I* X) when they are in series (because I is the same for all
components in series (Formally, an instance of Kirchoff's Current Law)

For your example, where C2 = 10 * C1, then X1 = 1/(2 *pi * f * C1) and X2 =
1/(2 * pi * f * C2) = 1/(2 * pi * f * C1 * 10) or X2 = 0.1 * X1.... So if
they are in series... V1 = I * X1 and V2 = I * X2, and since X2 = 0.1 * X1,
V2 = 0.1  * V1.......

>
> Some people are frightened by what they don't understand, others are
> fascinated by what they don't understand. I guess that is what makes me a
> coiler, I am fascinated by it, but I don't even understand the half.
>
> I am a programmer, and I remember the frustration I felt trying to
explain
> "Simple" concepts to people only to have them forget what I said. Now
that I
> am on the other side of the fence with having difficulty being able to
> remember the relationship between pico, nano, micro and to relate the
> symbols used. For example, I have no idea what uF means. I think it means
> Microfarads. Now I know how THEY feel!

It does, except the u is really a Greek "micro", but since we work on ASCII
keyboards, we approximate it with something that looks similar "u"...  Most
folks think it's less confusing than mfd (the old abbreviation) because
that might look like "milliFarads" = mF....

nanoFarad) use letters that also work in english....

>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Friday, October 06, 2000 2:35 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Cap question.
>
>
> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> Hi Tom,
>
> 	When you put the smaller caps in with these large caps, the smaller
> ones
> will eat all the stress.  The big caps will act much like a short and see
> little of the voltage.  Thus, they probably are not too good for the
> average tesla coil :-(
>
> Cheers,
>
> 	Terry
>
> At 07:01 AM 10/6/2000 -0700, you wrote:
> >I just got an offer for two 2uf 8kv caps.
> >When i series them the capacitence will be way too
> >high for my TC, but what i want to know is can i put a
> >lower value/voltage cap, or 2 like .047uf/1.2kv in
> >series to drop the total capacitence to a more useable
> >level? (i need about .033uf)
> >thanks
> >
> >--Tom
> >
> >PS: If anyone in the US could use two 8kv 2uf caps,
> >contact me in about a week and mabey we can work
> >something out.
> >
> >
> >__________________________________________________
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>
>
>

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