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Why +ve terminal of electrolytic caps must be connected to +ve of battery?

  1. Feb 21, 2012 #1
    Hi all,
    I have a doubt regarding electrolytic capacitor. Why the electrolytic capacitor should be connected to higher DC potential in the circuit. What happens if the opposite happens? Also how electrolytic capacitors must be used where varying voltage comes across it?

  2. jcsd
  3. Feb 21, 2012 #2


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    Science Advisor

    There is a very thin insuating layer of Aluminium Oxide on one of the plates of the capacitor. This was formed by applying a voltage to the capacitor.

    This layer is the dielectric of the capacitor, so it is very important.

    So, it is important that you don't reverse the polarity as this can destroy this thin layer.

    If you don't follow this polarity, the results get very messy.
    I have never seen one of these explode, but I know they do because I have cleaned up the sticky mess that results. The capacitors vomit their entire contents as a steaming hot, foul smelling, sticky mess.

    Just don't do it.

    I have seen circuits where an electro is used for AC but I wouldn't do it. You can get non polarized capacitors and these should be used where high capacitance is needed.
  4. Feb 21, 2012 #3


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    Staff: Mentor

    The oxide insulator is formed in the factory by electrolysis in the finished product, the oxygen reacts with the surface of the thin aluminium foil. If you reverse the working voltage, this oxide layer can be removed and the capacitor becomes a conductor.

    For AC usage, two capacitors are joined back to back, so this means one oxide layer is always being enhanced by the polarity.

    I've seen small electrolytics connected with reverse polarity disintegrate with a bang exactly like a fire cracker, throwing shredded material as from a firecracker everywhere, including in the student's hair.
  5. Feb 21, 2012 #4
    thankyou for replies.
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