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Transformer efficiency

Discussion in 'Electrical Engineering' started by Den, Aug 17, 2004.

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  1. Den

    Den Guest


    Can anyone give me an idea of typical transformer efficiencies.

    I've got a 120V input / 240V output 1kVA transformer.

    I assume that sticking a 1kW resistive load won't just draw 2kW on the input
    side, but 2*(1+x) kW. How big, typically, will x be?


  2. Don Kelly

    Don Kelly Guest

    Sticking a 1KW resitive load on the output side will result in (1+x ) KW on
    the input side. Even for a cheap 1KVA transformer the efficiency should be
    in the order of 90 % (i.e. x=0.1). If you put enough money into it (as would
    be the case for a 1MVA transformer) then efficiencies should peak in the
    Ivory soap level. (99 44/100 % pure (x<0.006). I have tested 3KVA
    transformers which peaked at about 98%- these are run of the mill production

    If the input is 2+X - you have a piece of junk. Note that when you step up
    from 120V to 240V the current steps down and power in, ignoring losses will
    be the same as power out.
  3. Den

    Den Guest


    Thanks for this. You've answered my question

    And I have made a public fool of myself by forgetting that V(1)I(1) =
    V(2)I(2) - I had somehow forgotten that the power is constant! Oh well it
    won't be the first time I've looked dumb!


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