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Mains relay contact protection

Discussion in 'General Electronics Discussion' started by liamharrison, Sep 28, 2012.

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  1. liamharrison


    Sep 28, 2012
    I have searched high and low and I just can't find a satisfying answer to this.
    I have a computer that uses 30W in standby(!) so I wanted to be able to turn it off with a relay.
    I gather that the SMPS inside the computer is an inductive load but to what extent? Do I need to protect the contacts? (most of the time it would only switch the computer in and out of standby, but I want to do it properly). Is it likely the computer, being a consumer electronics product has protection inside?

    Thanks very much
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The SMPS is a capacitive load (actually it is more complex than that, but that's close-ish) in that it rectifies the mains and charges a capacitor with it. Current leads voltage, but only for a part of the cycle. (and it depends if the maker has gone to the effort of power factor correction)

    You shouldn't have any problems switching it on and off with a relay. The surge current at startup can be high, so a relay with high current rating may be useful.
  3. liamharrison


    Sep 28, 2012
    thanks very very much!
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