How to safely drain a capacitor

Discussion in 'General Electronics Chat' started by davidridenour, Feb 18, 2010.

  1. davidridenour

    Thread Starter New Member

    Feb 18, 2010
    Hi, I'm new to this site and hope I can get a little help. I need to remove a motor from an old garage door opener for a project. It has a 220v capacitor attached and I don't want it laying around with a charge. What is the best way safely drain this capacitor? Any help will be appreciated.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Hook a 50K to 200K resistor across it. Resist the temptation of shorting it with a screwdriver, as I have ruined several screw driver tips.
  3. kdillinger

    Active Member

    Jul 26, 2009
    But that is the boring way!
  4. davidridenour

    Thread Starter New Member

    Feb 18, 2010
    Thanks guys!
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    Then I was a engineering student, one of my fellow students charged up a capacitor. Then he throw it at me and said catch. Of course I did catch it and got an electrical shock. I got pretty upset, but the other students in the lab was lying on the floor laughing. Not very funny for me, and very unsafe I must ad.
    Last edited: Feb 19, 2010
  6. cjdelphi

    New Member

    Mar 26, 2009
    I love the "TRUE" expression "It's not the voltage that kills you but the amps"

    Although, i've never once died from touching a 16v cap, however if i caught a 500v cap... could the same be said?.... it's the penetration of skin vs skin resistance that has me concerned as 9v is enough to kill someone if you stab someone and essentially inject them with 9v
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    No it is the current path that kill you. If the current pass through the heart a small current may kill you. Other places the only damage it will do is to cause burns. This is used in surgery daily. surgeons use electrosurgery as a knife or to stop bleeding.
    Also during normal conditions 9 volt will not kill you. I sometimes use the tongue as 9 volt battery tester
  8. someonesdad

    Senior Member

    Jul 7, 2009
    I suspect most folks don't know the technique of touching a 9 volt battery to the tongue to "test" it. You'll easily be able to tell the difference between a battery with a reasonable voltage between the terminals and a dead one.

    You can also test 1.5 volt batteries similarly. Wet the end of a finger, touch one end of the battery, and touch your tongue to the other end. You can distinguish between active and dead 1.5 V batteries this way.

    In both cases, the sensation is similar to a piece of aluminum foil in your mouth.

    Of course, if you think it's unsafe, don't do it. I've been doing it for many decades and most folks will attest to the fact that I'm as screwed-up as I ever was... :p
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    That's on a par with the technique of smelling a soldering iron to see if it's hot. Works just fine.
  10. Audioguru


    Dec 20, 2007
    Your tongue on a 9V battery to "taste" how many volts it has is a poor test since the battery is not loaded.
    Try a battery removed from a smoke dtector after 1 year. It measures 8.5V without a load so it is like new? No because when loaded it cannot provide much current to be useful for anything.
  11. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    Find a nice place near a flowing current and tickle her coil.