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Homework Help: Transformer efficiency/primary current (help )

  1. Feb 5, 2009 #1
    Transformer efficiency/primary current (help!!)

    Real transformers are not 100% efficient. That is, the efficiency, in percent, is represented by e = (100%) Ps/Pp. A step-down transformer has an efficiency of 92.5% is used to obtain 23.0 V from the 125 V household voltage. The current in the secondary circuit is 27.0 A. What is the current in the primary circuit?

    I have tried basically everything but I cannot seem to figure it out. Help???
  2. jcsd
  3. Feb 5, 2009 #2


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    Homework Helper

    Re: Transformer efficiency/primary current (help!!)

    If it was 100% efficient what current would need to be supplied?

    That means the power in is the power out.

    So what is the power out?

    Once you know the power in then you know that it needed to be more by how much? .92 of actual Power = Power you calculated as required to meet the statement of the problem.
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