Re: Capacitor - series?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Luke,

The two caps will not measure the same voltage if measured across each cap 
individually.

It's a simple capacitive voltage divider.
I'll use an example from Grob:

Xc = 1/(2piFC)

---------------------------
|                         | <--
|           C1 = 2uF     ---   | V1 = 40V, 1A
|          Xc1 = 40 ohms ---   |
|                         | <--
120 Vac                   |
|1A,2kHz                  | <--
|          C2 = 1uF      ---   | V2 = 80V, 1A
|          Xc2 = 80 ohms ---   |
|                         | <--
---------------------------

Hope this helps,
Bart



Tesla list wrote:

>Original poster: "Luke" <Bluu-at-cox-dot-net>
>Ok all this has me a bit confused.
>I am STILL of the inclination that:
>the two caps WILL NOT see the same voltage
>if they are of DIFFERENT VALUES.
>
>Some are saying they will see the same voltage.
>
>What seems to be the verdict among the guys that know their stuff?
>
>Luke Galyan
>Bluu-at-cox-dot-net
>
>-----Original Message-----
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Sunday, February 08, 2004 3:06 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: Capacitor - series?
>
>Original poster: Mddeming-at-aol-dot-com
>
>
>Hi Phil,  (see interspersed comments)
>
>     In a message dated 2/8/04 2:25:06 PM Eastern Standard Time,
>tesla-at-pupman-dot-com writes:
>
>SNIPPPP
>
>  >Firstly, at ac, just pick a frequency, calculate Xc, treat them as two
>  >(or 5) resistors & see what you get.  Better still wire it up & get
>out
>  >your meter - this you can measure.
>
>Yeah! Scientific method!  Unfortunately, far too many people are willing
>to
>jump right to opinion without this step.
>
>  >The voltage will divide across capacitors in inverse proportion to
>their
>  >capacitance - i.e. in direct proportion to their reactances, just as
>if
>  >they were resistors.
>Correct.
>  >It is the same for DC, can be explained by conservation of charge, but
>  >is harder to measure.  Well not really, just use a DMM & uF range
>caps.
>  >[Time constant = (10M Ohm x 10uF) = 100sec - long enough to measure]
>
>  >Because the circuit does not see the full
>  >capacitance of any single capacitor in series, you can't use that
>  >individual cap value to figure reactance because that caps true value
>is
>  >never "felt" by the circuit.  See my other reply.
>
>  >It matters less in this discussion what the circuit sees than what the
>  >individual capacitors see. In any case whichever way you do the maths
>  >you get the same result.
>
>  >The two capacitors -are- two discrete components. The electrons flow
>out
>  >of one & into the other. It makes sense to discuss their parameters
>  >individually, which was the point of the original question.
>
>Yes!!
>
>  >If the original question's basic intent is something like: "Will one
>or
>  >both capacitors blow up when used in a TC tank circuit ?" then my
>answer
>  >would be along the lines of 'Not necessarily with those two examples
>  >(equal C.V products), but often yes.'
>
>  >Sure the smaller cap governs the charging characteristics & limits the
>  >maximum charge of the combination - when it's charged the current
>stops
>  >flowing & they both stop charging. So it is more nearly fully charged,
>  >and the larger cap less fully charged (To its capacity, I mean. The
>  >absolute Charge contained in each cap is the same.)
>Yes!!
>
>  >In any given instant or cycle or whatever, the same current has flowed
>  >through each capacitor. So they each hold an identical charge - no of
>  >electrons. But a given amount of charge, if you like, concentrated in
>a
>  >smaller volume (capacitance) results in a higher pressure (voltage) &
>  >vice-versa.
>
>  >Q = C.V  ->  V = Q/C    That pretty much says it.
>
>
>  >Phil Chalk.
>
>   Of course, you are right. You obviously have a sound understanding of
>first principles, but it is amazing how much mis-information one can
>find,
>even on this list. What frightens me is the number of Newbies and
>Not-so-newbie "self-ordained experts" who are actively working with high
>
>voltages and advising others, with only a minimal (or less)
>understanding
>of basic principles of electricity. This capacitor question is only one
>small example of the larger problem.
>
>There was a time when cost of publication and peer review acted as B.S.
>filters, but now anyone with an opinion and the price of a keyboard can
>"fertilize" the whole Internet in a matter of minutes. While I am in no
>way
>in favor of censorship of the list, it would be nice, (but practically
>impossible) if statements that are blatantly contrary to all known
>physical
>laws could be annotated as such before being rebroadcast. Oh well, I
>guess
>our after-the-fact reviews are the best that can be done. I just hope
>that
>newbies can figure out who is "blowing smoke" before they blow their
>coils,
>their instruments, or themselves up in smoke.
>
>Matt D.
>
>
>
>