Charging a capacitor with AC voltage

Discussion in 'General Electronics Chat' started by p75213, May 27, 2012.

  1. p75213

    Thread Starter Member

    May 24, 2011
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    Can somebody explain how it is possible to charge a capacitor using ac voltage? The way I see it is the capacitor wouldn't have time to charge as the voltage is constantly switching. In the case of 60Hz - 120 times a second.
    The attachment shows a tesla coil where the capacitor is in series with a primary coil and the source is a transformer. A spark gap is in parallel with the source and capacitor/transformer. I can't see how the capacitor will charge.
     
  2. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    That capacitor has no intention of charging to a DC voltage. It is designed to work in conjunction with the coil at an AC frequency.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,010
    3,233
    A capacitor can readily charge and discharge to the AC voltage level. High frequency type capacitors with low parasitic inductance can charge and discharge at up to GHz frequencies.

    A capacitor can theoretically charge and discharge instantaneously. It's the resistive and inductive stray values in series with the cap that limit its frequency response.
     
  4. p75213

    Thread Starter Member

    May 24, 2011
    39
    0
    Thanks for that crutschow.
    I never realized they could charge and discharge so quickly. Given that i=Cdv/dt the voltage change would have to be less than instantaneous otherwise you would end up with infinite current.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,010
    3,233
    Of course an instantaneous change of voltage on a capacitor would require an infinite current. But with a low impedance in series with the cap, the charge and discharge can be very fast.
     
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