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Solve for Req with T to Delta Transform

  1. Sep 26, 2016 #1
    1. The problem statement, all variables and given/known data
    Find Req in the given circuit
    upload_2016-9-26_13-10-23.png

    2. Relevant equations
    Series: req = r1+r2...
    parallel: 1/req = 1/r1 + 1/r2 ...

    3. The attempt at a solution
    Without redrawing the circuit I do:
    12||60 = 10
    10+20 = 30
    30 || 30 = 15
    15+10 = 25
    25||25 = 12.5
    12.5+15+5 = 32.5 = Req
    This is the correct answer.

    upload_2016-9-26_13-10-3.png
    However if I redrew the T to a delta I no longer can get the right answer.
    108 || 0 = 0
    (36 || 30) || (180 || 10) = 6
    6||25...
    and so on

    Where am I going wrong in my logic? Am I not allowed to do this sort of transformation on this problem?
     

    Attached Files:

  2. jcsd
  3. Sep 26, 2016 #2

    The Buttered Cat

    User Avatar
    Gold Member

    Why is the 180 in parallel with the 10?
     
  4. Sep 26, 2016 #3
    I completely looked over the 25 ohm resistor when I did that. Thanks.
     
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