Thevenin Equivilant help

Discussion in 'Homework Help' started by Boboulas, Dec 12, 2010.

  1. Boboulas

    Thread Starter New Member

    Dec 12, 2010
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    [​IMG]
    Please see attached i need to work out the equivilant thevenin circuit to the left of AB

    what is the process for thevenin when you have two voltages like this?

    i have already worked out the resistance = 1.62Ω

    any help would be appreciated

    http://yfrog.com/5xtheveninj
     
    Last edited: Dec 12, 2010
  2. tyblu

    Member

    Nov 29, 2010
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    Thevenin voltage is the open circuit output voltage, which is how it's already setup, so simply calculate the voltage from A to B. One way is to use superposition: short source #2 and calculate V_{\small{AB,1}} using only source #1, then short source #1 and calculate V_{\small{AB,2}} using source #2, and finally add the two together to get V_{\small{Thevenin}} = V_{\small{AB,1}}+V_{\small{AB,2}}.
     
  3. Boboulas

    Thread Starter New Member

    Dec 12, 2010
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    So therefore:
    4V VAB1= 5/8*4=2.5V
    6V VAB2= 5/17*6=1.764V

    VT = VAB1 + VAB2
    VT = 2.5V + 1.764
    VT = 4.264V

    Is this correct?
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    No,
    For 4V Vab_2 = (3||5 ) / ( 12 + 3||5) * -4 = -0.54054054V

    For 6V Vab_2 = ??
     
  5. Boboulas

    Thread Starter New Member

    Dec 12, 2010
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    For 6V = (12//5) / (3 + 12//5) * 6 = 3.243

    therefore

    3.243 + - 0.540 = 2.703 V

    is this correct? am i getting any closer to grasping this?
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    You are very close to get the right answer.
    In your diagram all voltage source have positive terminal point toward point B.
    So this mean that voltage on point B has
    higher potential than point A

    So correct answer will be ??
     
    Last edited: Dec 13, 2010
  7. Boboulas

    Thread Starter New Member

    Dec 12, 2010
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    im sorry im not sure, have you any more help or hints?
     
  8. Boboulas

    Thread Starter New Member

    Dec 12, 2010
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    does that mean it will just be a negative result?

    Therefore: revised:

    For 6V = (12//5) / (3 + 12//5) * -6 = -3.243

    therefore

    -3.243 + - 0.540 = -3.783 V
     
  9. Jony130

    AAC Fanatic!

    Feb 17, 2009
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  10. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Yes you right.
    Vth = -3.783 V
     
    Boboulas likes this.
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