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substitute d/c cap. for a/c?

Discussion in 'Electronic Components' started by Richard, May 27, 2004.

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  1. Richard

    Richard Guest

    I blew out a 1 mfd 120v.a/c cap. in my OLD generator automatic switch and
    can't find a replacement. I was wondering what I can use for a substitute?
    The original is a can about 7/8"D. X 1-1/2" long, wound tinfoil
    inside(was):) and a lead out each end. Would a 1 mfd. 400v.d/c work? what
  2. I think the main thing is that it needs to be a capacitor that isn't
    sensitive to polarity, i.e., a plastic film capacitor of some type rather
    than an electrolytic. Plastic film capacitors don't have positive and
    negative ends. I suggest one that is rated at 250 volts.

    The maximum voltage rating might still be expressed as DC volts; that
    doesn't make it a DC capacitor.
  3. Dave Platt

    Dave Platt Guest

    The "AC" rating might also indicate that the cap needs to be able to
    tolerate high ripple currents (i.e. have low internal losses, or be
    resistant to degradation due to the heat generated by its losses)
    and/or might need to be safety-rated for connection across power mains
    (e.g. the X2 safety rating used these days).
  4. Good point. He should use a capacitor that is designed for use with
    line-powered AC motors, for safety's sake.
  5. Use an X2 rated capacitor. You can find X2 caps in old AT power
    supplies. THey're usually something like .47 uF or 470 nF, at 240VAC.
    You could put two in parallel for about 1 uF.
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