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Switch ratings conversion from AC to DC

  1. Sep 1, 2011 #1
    I have a push-button switch rated at
    3 amps @ 125vAC

    which I want to use in a 12v DC application (my motorcycle).
    ((on ground line under continuous use {headlight}))

    Does the AC rating translate as

    3 amp for 125v AC hence 375 watts

    375 watts for 60v AC hence 6.25 amps


    375 watts for 12v DC hence 31.25 amps

    This calculation doesn't seem right but I was thinking that the point at which the switch will fail is determined by the Number of Electrons flowing thru the contacts at any moment in time and isn't that better represented by watts than amps??

    Why would the switch fail above 3 amps no matter what the volts ?? This doesn't seem right to me either.
  2. jcsd
  3. Sep 1, 2011 #2


    User Avatar

    The switch has some resistance R. The power which is dissipated on it is RI2. If you use it for higher current than it is designed for you may just burn the contacts.

    Regarding voltage - you cant use the switch for higher voltage than it is designed for - as it may spark between contacts (don't use US switches for European AC!). But you may, of course, use it for lower voltage - like in your case.
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