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Connected the capacitor to a DC power supply

  1. May 9, 2008 #1
    A few days ago, I was in the lab doing some experiments with capacitors and something weird happened...

    I connected the capacitor to a DC power supply and after a few seconds the capacitor has popped. The voltage applied to it was within its working voltage, so that was not the cause. My lecturer then told me that I connected the leads to the capacitor the other way round and he was right. Then I asked him the following question in which he was unable to answer it...

    If I have a DC power supply and connect the leads to the capacitor in the wrong way, it will pop! This means that the current is only allowed to flow in one direction... So why don't they pop with an AC power supply?
     
  2. jcsd
  3. May 9, 2008 #2

    NoTime

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    What make you think they don't?
     
  4. May 9, 2008 #3
    Probably, they do, but that's not my question...
     
  5. May 10, 2008 #4

    NoTime

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    Only question I see. Your proceeding statement is correct.
    Perhaps you can clarify what your question is then.

    Edit: Ok, Not thinking. Charge can move into and out of the cap as long as the voltage polarity remains the same.
    So your proceeding statement is not quite correct.
     
    Last edited: May 10, 2008
  6. May 12, 2008 #5
    I would assume that the capacitor to which you refer is an electrolytic...

    Aluminium Electrolytic capacitors rely on the thickness of a film of oxide formed on the plates inside the capacitor.

    Unless the electrolytic is a reversible type, the thickness of the oxide films on the positive & negative films is different.

    Therefore, when the capacitor is reversed, the thinner film breaks down, large currents flow & the electrolyte heats up.

    Then the can pops.

    This is dangerous... the bigger the capacitor, the more dangerous it is...
     
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