Wallwart holds charge even when unplugged.

Discussion in 'General Electronics Chat' started by blah2222, Nov 4, 2012.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Hi, I picked up a wallwart with adjustable voltage settings 1.5 thru 12V but noticed that it does not discharge when unplugged.

    Wondering if anyone has any suggestions to tackle this. It discharged 12V in around 3 - 5 seconds with a 560ohm resistor.

    Thanks,
    JP
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    So it has a 4700μF filter capacitor. Does this create a problem?
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Yup! That's what capacitors do. Hold a charge. Not unusual at all in a power supply. Capacitors also reduce the ripple voltage. Usually exactly what you want - a power supply with a DC output with low ripple. A good quality capacitor can hold a charge for days if there is no dischagre path.
     
  4. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    The capacitor value used in this case isn't much to worry about. Unless you're going to lick it at 12V, it's not going to do any damage. I can think of only one way this could damage something, and that's the short duration of over-voltage when plugged into some other device, but that seems to be to be unlikely.
     
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