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Help needed, equivalent resistance of this circuit

Discussion in 'General Electronics Discussion' started by jrios, Jan 2, 2014.

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  1. jrios

    jrios

    2
    0
    Jan 2, 2014
    Need to know which is the equivalent resistance of this scheme between the points A and B and and how do you know it. Thanks in advance, I'm not able to solve this problem myself...

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  2. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    The given resistor network contains an unbalanced Wheatstone Bridge which cannot be solved by simple series/parallel analysis. The following web page, http://www.allaboutcircuits.com/vol_1/chpt_10/3.html, recommends solving the unbalanced bridge using mesh currents and provides an example. As an alternative there is a solution using node voltages for the general case shown in the pdf attachment. Note that the equivalent resistance is calculated as Req= V0/I0 = V0/(I1+I2).
     

    Attached Files:

  3. jrios

    jrios

    2
    0
    Jan 2, 2014
    Many thanks, Laplace! I didn't know about Wheatstone Bridges, so I had no idea how to solve it. Now i'll study the method in the pdf and will try to do it with mesh currents too. It's a tricky circuit I'm so glad I find a solution for this. Thanks again man.
     
  4. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    you can shovel it into the free ltspice simulator and put a voltage across it and see what current flows from the voltage source...V/I will give you the resistance
     
  5. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    A quick method to get a very close answer is to remove the middle resistor 3R then solve as normal. The middle resistor can be removed because it has virtually the same voltage between its two terminals to within 16mV. This then becomes 8.7R.
    Thanks
    Adam
     
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