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Capacitors

Discussion in 'Electronic Basics' started by Mike, Nov 10, 2004.

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  1. Mike

    Mike Guest

    Am I right in thinking that it's the ripple current property of a capacitor
    that makes it suitable for discharge experiments? When I say discharge
    experiments I mean discharging the capacitor as quickly as possible (e.g.
    coilguns, railguns etc etc). Should the ripple current be as high as
    possible (e.g. 5A is better than 4A)?

    I've seen some capacitors, which are described as suitable for discharge and
    pulse applications. But the ripple current seems to be smaller than other
    standard capacitors (of the same size and voltage). The capacitor has the
    following specs:

    400V
    1000uF
    Ripple Current 4.05A

    Here's the data sheet of the capacitor if anyone's interested:

    http://www.farnell.com/datasheets/7958.pdf

    Any ideas?
     

  2. There are (at least) two important aspects of a caps ripple current
    rating. One involves how much internal resistance the capacitor has
    that generates heat as ripple current passes through it. The other is
    the capacitor's ability to get rid of this heat through its surface
    and its ability to handle the internal temperature rise this process
    requires. But if all other properties were exactly the same, it is a
    pretty safe bet that the one rated for higher ripple current would
    stand a rapid discharge process better.
    It looks suitable for some rate of discharge to me. ;-)
    Have you calculates what RMS ripple current (over a full cycle time)
    your circuit will produce? Maybe it is way more or less than these
    specs and you are worrying about nothing or way off base. Start with
    what you need.

    The ultimate specification for rapid discharge applications is fusing
    current. This is the I^2*T that will melt the internal current path
    somewhere. When you find one with this kind of spec, you know they
    designed it for big pulses.
     
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