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Can capacitors collect ambient energy?

Discussion in 'General Electronics Discussion' started by Damname101, Nov 26, 2011.

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  1. Damname101


    Nov 26, 2011
    I have been fiddling with a couple 330uf 200v caps and am finding that
    they are someone gaining charge while just sitting around. They tend to
    gain about .03v to .09v after being shorted out and left to sit.

    Is this normal? Are they collecting energy from the environment? Is it
    ambient EM energy?

  2. davenn

    davenn Moderator

    Sep 5, 2009
    not that Im aware of
    .03 - .09V could still be within the realms of the error range of your multimeter

  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It's not too unusual. I have some caps that will get a few volts across them if you leave them charged, then briefly discharge them.

    Capacitors are essentially 2 conductors seperated by an insulating layer.

    WHen you charge them, you place a tension acrosss the insulator (caused by an electric field) which tries to pull the excess electrons from one side to the side with a deficiency of electrons.

    Some of these electrons are pulled right through (this is leakage in the capacitor). Some get pulled part way through.

    The ones that get pulled part way through can't get out of the insulator when you briefly discharge the capacitor. Now that the force pulling them into the insulating layer is gone, they slowly return to nearer the surface.

    This "stuck" charge appears to com from nowhere to re-charge the capacitor. In fact, it is part of the original charge that couldn't discharge quickly.

    I discovered this effect in capacitors used to hold a charge in camera flash units. I thought I was mad, geting a small tingle from a capacitor I had already discharged.

    The effect is much stronger (apparantly) in the capacitors used to in microwave ovens. The charge they can re-build up can be enough to kill you. Safety precautions when handling these capacitors includes keeping a shorting strap on them.
  4. Laplace


    Apr 4, 2010
    The technical term for this effect is capacitor soakage or dielectric absorption.
  5. Damname101


    Nov 26, 2011
    thanks all, very insightful :)
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