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Re: Wiring caps in series




>Date: Sat, 7 Sep 1996 16:46:20 -0400 (EDT)
>From: "Kevin D. Christiansen" <kdc4n-at-cs.virginia.edu>
>To: tesla-at-pupman-dot-com
>Subject: Wiring caps in series
>
>
[snip]
>As an experiment, I tried wiring 6 of them in series and then
>running them through several charge/discharge cycles of 1500 volts -
>by putting 1500 volts between points A and G (see "schematic" below),
>and then bridging points A and G with a heavy wire (BANG!!!).
>
>    ||  ||  ||  ||  ||  ||
>  o-||--||--||--||--||--||--o
>    ||  ||  ||  ||  ||  ||
>
>  A   B   C   D   E   F     G
>
>The first time I charged them up, each of the caps had about the same
>voltage across them (Vab=Vbc=Vcd=Vde=Vef=Vfg=250 volts).  After
>dischaging them by bridging A and G with a wire, I assumed that all
>of the caps would have discharged to some low value.  What I found
>instead is that the caps had more or less random voltages on them
>(between -50 and +50 volts).  Charging the set up again (by putting
>1500 volts across points A and G) resulted in widely varying voltages
>across the various capacitors.
>
>Given this situation, I could easily see some of the caps failing
>due to over-voltage conditions, which are caused by the varying
>voltages that result when the capacitors are charged and discharged
>in series.

This is happening because the cap are not exactly equal values.

Equalizing resistors must be placed across each cap to balance the
voltage drop across each one. Use T = RC as a starting point to set
the value of the equalizing resistors. T will be the time to equalize
and C will be the value of each cap. Watch out for exceeding the
voltage and current limits of the resistors.

	jim