how to discharge a capacitor?

Discussion in 'General Electronics Chat' started by simpsonss, May 31, 2010.

  1. simpsonss

    Thread Starter Active Member

    Jul 8, 2008

    After i power off my circuit then i measure the voltage across the big capacitor.It still having 100V on it.How can i discharge this capacitor?I tried to use a high wattage resistor and tap one end to the capacitor positive leg and another end to GND. But it seems like discharging very slowly.Any idea?

    thank you.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    It is safer to use clip leads to place a resistor across the terminals of the capacitor. Use some value that limits current to a reasonable value, and enough dissipation so it does not get cooked.

    For your 100 volts, anything around 10,000 ohms will keep current down to 10 ma. Just leave the clip leads attached for a few minutes, as it takes a bit to pull the charge down through the resistor. The diminishing voltage means the discharge current drops with it.
  3. SgtWookie


    Jul 17, 2007
    You could use a ordinary 120v light bulb. The nice thing about using a light bulb is that the resistance is non-linear. This means your cap will be discharged a lot more quickly than if you used a fixed resistor.
  4. dlhylton

    New Member

    Jan 24, 2012
    One way to discharge a capacitor is by shorting the two leads of the capacitor together. However, this should only be done with capacitors holding a very low voltage; otherwise, the current generated will be high and this can prove dangerous.

    The second, more safer way, to discharge a capacitor is through a load, usually a resistor. Connect the two leads of a capacitor to a large resistor, several megohms, and the capacitor will discharge its voltage through this resistor. Although this method takes longer, it is more safer.

    For more info, check out:
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
    dlhylton, did you notice this thread is two years old? :p
  6. panic mode

    Senior Member

    Oct 10, 2011
    maybe capacitor still holds charge ;)
    CQCmaster and DerStrom8 like this.