Voltage division along NON-equal caps in series? (fwd)

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---------- Forwarded message ----------
Date: Mon, 10 Sep 2007 13:51:11 EDT
From: FIFTYGUY@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Voltage division along NON-equal caps in series?

Folks-
 
    I've got a number of caps of varying ratings that  I'm considering 
combining for primary tank use.
 
    I know we assume equal sharing of voltage between  identical caps in 
series. 
 
    But what about non-identical caps? I know that an AC  voltage will be 
seen across the caps as if it was a resistive voltage divider,  with the 
reactances of the various caps corresponding to the voltage seen across  each. In this 
case, larger caps will have smaller reactances, and the voltages  across them 
will be proportionately smaller. 
 
    But what about the DC case? The primary charging  frequency is so low, we 
consider the DC case. And here's where I get confused.  It seems 
(intuitively) that if each cap was a single plate, then the voltage  would be distributed 
evenly between each cap, no matter what the area of  each plate may be. I 
could also see that the spacing of each  plate could play a role as well - the 
thinnest dielectric in a series of plates  would have the highest voltage stress 
(intuitively?).  But what if some  caps have many internal plates, and some 
have only one? Does cap value have any  effect on the DC voltage seen across it 
when it's in series with other  caps?
 
    For instance, if I have a 1uF cap, a 10uF cap, and  a .1uF cap in series, 
and I put them in series, and put 1V DC across this series  arrangement, how 
is the 1V DC distributed across them? Are the particulars of  their 
construction important?
 
    Does this sort of mismatch cause problems during TC  use?
 
    Thanks!
 
-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities



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