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Re: Wiring caps in series
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HI,
Make sure you place a large value resistor (1meg ohm) across each capacitor
to
equalize the voltages. These caps are (probably)electrolytics and have
10-15% tolerance on the capacitance values. As a result the voltages would
be different as you discovered and would continue to vary with each cycle.
You shouldn't cycle these caps very rapidly either, and I think dead shorts
(wire discharge) are hard on them. Certainly NOT TC caps.
Dave
----------
> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Wiring caps in series
> Date: Sunday, September 08, 1996 9:25 PM
>
> >From kdc4n-at-cs.virginia.eduSun Sep 8 20:04:32 1996
> 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
>
>
> A little while ago, somebody on this list asked if it would be
> practical to make a high voltage capacitor by wiring a bunch of photo
> flash (330 V 160 uF) caps in series. I never saw an answer to this
> question.
>
> 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.
>
> Today, sombody mentioned (in the discussion on "paper capacitors")
> that Tesla used his caps in series:
>
> Tesla List writes:
> > >From i541771-at-imsday-dot-comSat Sep 7 09:37:34 1996
> > From: Chris Singletary <i541771-at-imsday-dot-com>
> > > From: Tesla List <tesla-at-poodle.pupman-dot-com>
> > > >From hullr-at-whitlock-dot-comThu Sep 5 22:16:22 1996
> > >
> > >
> [snip]
> > I believe that you mean Maniton (not Manitou) water bottles and while
> > he did have then break from time to time he attributed it to a a
cascading
> > effect. The bottles (is placed in series) were able to withstand an
> > EMF of 30,000 safely and stated that he thought the glass was
> > excellent.
> [snip]
>
> What did I do wrong in my experiment?
>
> I am currently doing (very low budget) experiments with large
> flash lamps, and would love to make large capacity, 5000 volt
> capacitors by hooking lots of photoflash capacitors (which I
> can get for almost free, from those disposable cameras) in
> series. It seems that other people have built high voltage
> caps by connecting lower-voltage caps in series. What must be
> done in order to avoid the over-voltage conditions that occur
> when they charge/discharge unevenly?
>
> Thanks for any help/suggestions you can give me!
>
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> Kevin D Christiansen
> User Interface Group - The University of Virginia
> "The best VR that pizza can buy"
> kevin-at-virginia.edu http://www.cs.virginia.edu/~kdc4n/
>
> "The universe is composed of space, galaxies, and intergalactic
> dust. Galaxies themselves are composed of space, stars, and
> interstellar dust. From the omnipresence of dust, we conclude
> that nature abhors a vacuum and won't pick up a broom, either."
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-