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Reverse polarity capacitor

Discussion in 'General Electronics Discussion' started by giftiger_wunsch, Aug 21, 2016.

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  1. giftiger_wunsch

    giftiger_wunsch

    1
    0
    Aug 21, 2016
    Hi,

    I have little experience with electronics, ad even less recent experience, and I prototyped a circuit on a breadboard and got the polarity of a 220uF electrolytic capacitor wrong, before realising my mistake and swapping it around (and learning that reverse-polarity capacitors can, in fact, explode). While looking at the physics behind that I read that it's caused by the rapid breakdown of an aluminium layer in the capacitor which will then cause the electrolytic to boil and build up pressure if used for an extended period.

    My circuit was a 555 monostable configuration which took a momentary radio input and produced a 5 second pulse. From what I understand of the monostable circuit, the capacitor spends most of its time charged in that configuration, so it's probably fair to say it's spent a good half hour partially charged with polarity reversed.

    My question is, if I've muddled the polarity but not caused it to catastrophically fail, is it now unsafe to use with the correct polarity because of the deterioration of that Al layer? Should I throw it out? I have a good dozen more which I'm never going to use, so to be on the safe side I'd probably throw it out, but I'm curious to know whether it's necessary.

    Edit: it's a 50V capacitor and the circuit was 5V

    Thanks in advance.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    Your call is probably OK.

    The reverse polarity you applied was only 10% of the maximum forward polarity. The cap can probably withstand it.

    There is a reasonable possibility that its forward voltage has been temporarily reduced, but again you're only planning to use it for 5V.
     
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