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10V ceramic cap at 95V DC ?

Discussion in 'Electronic Design' started by Adam S, Apr 1, 2007.

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  1. Adam S

    Adam S Guest

    I was wondering what happens when you put too much voltage across a one
    of those low voltage multilayer ceramic capacitors. I took a 2.2uF 10V
    X7R in 1206 package, and applied 95V across it and nothing exciting
    happened. Leakage settled to 0.5uA after 2 minutes. Even after
    disconnecting for 1 minute the terminal voltage was around 60V+. The
    only thing I noticed was capacitance had dropped from 2.30uF to 1.85uF
    (at 0 VDC bias) after the test. However heating the capacitor with a
    soldering iron tip for a second , had restored it to its original 2.30uF.

    So what bad things are suppose to happen when you exceed the 10V spec. ?
     
  2. Uwe Bonnes

    Uwe Bonnes Guest

    As you have seen
    - Polarization gets lost (perhaps recoverable)
    and more
    - Capacitance at that high voltage drops considerably
    - At some point in time or at some higher voltage the part will spark or
    something like that

    Bye
     
  3. colin

    colin Guest

    I was making a EFL inverter, it had some 1nf 1205 400v caps in the filter,
    when I was trying to get it to work ocassionaly the thing would resonate and
    get so excited
    sparks would jump acros the endcaps of the capacitors !

    I was surprised the caps hadnt failed and gone short circuit, it was quite
    spectacular.

    Ive used some 10uf ceramic caps in a low leakage integrator application,
    I measured the total leakage in the circuit and it was the same as the
    leakage through the glass fiber pcb.
    theres probably good reason why the guaranteed specs are seemingly somewhat
    pessimistic.

    Colin =^.^=
     
  4. Joerg

    Joerg Guest


    Be careful if that comes off a low impedance source. I have seen ceramic
    turn into bubbly green glass with a loud bang.
     
  5. Ian

    Ian Guest

    ISTR some information (AVX site?) saying that most ceramic caps will
    survive several times the rated voltage, it is just that a few per batch may
    not.

    Regards
    Ian
     
  6. Joerg

    Joerg Guest

    Sounds like Russian roulette ;-)
     
  7. Adam S

    Adam S Guest

    I only tested a couple of caps and didn't go higher that 95V on a 10V
    rated device. Its interesting watching such a tiny thing make a nice
    little blue spark when shorted.
     
  8. Tim Williams

    Tim Williams Guest

    Hmmmmm. Methinks I want to buy a reel of a thousand, build an automatic
    testing machine, and assemble the remaining ones (being made almost entirely
    of magic smoke, the bad ones remove themselves from the machine with the
    assistance of a small fan) into a rather large capacitor. Whaddya think,
    energy density comparable to aluminum electrolytic at least? ;o) Power
    density through the roof!

    Tim
     
  9. Rich Grise

    Rich Grise Guest

    On Mon, 02 Apr 2007 17:39:23 -0500, Tim Williams wrote:
    [top-post repaired, see below]
    If you've got the money, I've got the time! ;-)

    Good Luck!
    Rich
     
  10. Tim Williams

    Tim Williams Guest

    College student :-(

    Tim
     
  11. Rich Grise

    Rich Grise Guest

    No, starving Contract Inventor. ;-)

    Or, depending on how hungry I am at the moment, I can do grunt work.

    Let's face it, who amongst us isn't a whore, some of us merely priced
    higher than others? >:->

    Thanks!
    Rich
     
  12. whit3rd

    whit3rd Guest

    The X7R and BK (and some other) capacitor ceramics are nonlinear
    (actually ferroelectric), and the problem with overstress isn't
    leakage or explosion. It's capacitance-value-droop. And as you
    saw, the value stays out-of-spec after the stress is removed.
    At 95V, if you'd measured it (put a known-good capacitor in series
    and voltage-stress it then measure the series pair under voltage),
    you might have found 0.2 uF.

    A buddy of mine was trying to measure capacitors for a filter. He
    never got the same value twice from the digi-bridge. I saw the
    markings on the capacitor and laughed- it was the heat from his
    fingers
    as he handled the caps that made 'em always a few percent off
    on successive measurements. Nonlinear materials are great for
    energy density and in applications when you care little for AC
    dissipation. They don't really obey the straight capacitance equation
    very well, though.
     
  13. Tim Williams

    Tim Williams Guest

    Churchill: Madam, would you sleep with me for five million pounds?
    Socialite: My goodness, Mr. Churchill... Well, I suppose... we would have to
    discuss terms, of course...
    Churchill: Would you sleep with me for five pounds?
    Socialite: Mr. Churchill, what kind of woman do you think I am?!
    Churchill: Madam, we've already established that. Now we are haggling about
    the price.
    (From: wikiquote.org.)

    Tim
     
  14. Rich Grise

    Rich Grise Guest

    That's an old Playboy Party Joke. The "real" Churchill quote, which
    probably actually came from W.C.Fields, was:

    Dowager: "Mr. Churchill, you are drunk!"
    Churchy: "Madam, you are ugly. Tomorrow I shall be sober."

    And then there's the one where a guy walks into a bar and sees a gal
    with a duck under her arm:

    Guy: "Hey, where did you get the pig?"
    Gal: "That's an old joke!"
    Guy: "I was talkin' to the joke."

    Cheers!
    Rich
     
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