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Homework Help: DC Machines

  1. Aug 24, 2008 #1
    1. The problem statement, all variables and given/known data
    A dc machine(6W, 120V,1500rpm) is separately excited and delivers rated current at rated terminal voltage.Field winding is connected to 120V supply. Rfw=100[tex]\Omega[/tex].
    a) Determine the value of field current
    b) Determine the value of Rfc required.

    2. Relevant equations
    Vf= IfRf

    3. The attempt at a solution
    In the question the value of Vf is given, while both If and Rf are variables. So I need another relation to find out both the values. Is there another relation that I'm missing?
  2. jcsd
  3. Aug 24, 2008 #2
    Unless I misunderstand the problem, you can get everything you need from the power equations P=IE and P=I^2*R.
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