resistor network

Discussion in 'Homework Help' started by Nano_Dav, Oct 18, 2013.

  1. Nano_Dav

    Thread Starter New Member

    Oct 18, 2013
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    Hello everybody,

    I am having some issue to analyze a resistor network i am working on.

    I was able to analyze a more simple one but i am stuck on this one.

    The network is shown on the attached file.

    I know the resistors values (21 resistors in total) and the source voltage as shown on the pdf.

    I would be glad if someone can help me a little on that. basically i want to find node voltage and current through each resistor. Any clues is good for me !

    Let me know if you need more details.

    Thanks for helping and for your time.

    David
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    You need to show YOUR best effort to solve YOUR homework problem. It doesn't have to be great, but it does have to exist. That is what gives us a starting point from which to guide you toward a workable path.
     
  3. Nano_Dav

    Thread Starter New Member

    Oct 18, 2013
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    well, i wish it was homework, but I'm done with school ...

    After simplifying the circuit to that point, I was able to begin noting the current equation and voltage equation of some nodes (the ones near the voltage sources). I am stuck at node BCGH , for ex: i7=i8+i10 ? i8=i4+i12?

    I'm not sure what to do there?

    I m not looking for solution , but just a starting method/way/clue/suggestion ...

    thx again,

    David
     
  4. WBahn

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    Mar 31, 2012
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    We are not mind readers! How can we know what direction i7 or i10 is going? And BCGH is not a node. There are four different nodes, B, C, G, and H. So what do you mean when you say node BCGH?

    It's very likely that your problem stems from how you are viewing what you are doing. But we can't even guess at that until you show us exactly what you are doing by showing your work.
     
  5. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    There a number of things that are not clear about your schematic.

    At the very top left, the top end of a 1 ohm resistor seems to have a number appended; it looks like 1.5--does that mean that 1.5 volts are applied there?

    If that is so, where is your reference node? Where is "ground"?

    At the ends of a number of other resistors I see what appears to be "0"; does that mean zero volts? Are all those points grounded? Perhaps all of those zero labeled points are connected to, and constitute, your reference node.

    One of the resistors connected to node c looks like it might be 4 ohms; is it?

    Two of the resistors connected to node k look like they might be 20 and 24 ohms; is this right?
     
  6. WBahn

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    Mar 31, 2012
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    My best guess is that, indeed, the numbers at the ends are voltages (1.5V and 0V).

    At first I thought the numbers next to the resistors were meant to be resistances, but now am not sure. They may just be indexing the resistors since they run from 1 to 21.

    Gee, wouldn't some units clear things up nicely?
     
  7. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    You're right; they do appear to be indexes. Of course, they could be resistances as well. :D

    Maybe he means for them to be symbolic, as R1, R2,...R21.

    Whether numeric or symbolic, the solution is going to be a mess.
     
  8. Nano_Dav

    Thread Starter New Member

    Oct 18, 2013
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    sorry for the bad notation, indeed there is only two voltage 1.5 and gnd (0) , indeed these are resistance "name" (my bad R1..R21) and not values. good call electrician and WBahn. i was hoping you could help me find the Kvl/kcl or any other way to analyze this network. A starting point/example ?

    Thanks guys,

    David
     
  9. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Show us the simpler network you were able to analyze, and show the procedure you used to analyze it.
     
  10. Nano_Dav

    Thread Starter New Member

    Oct 18, 2013
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    here is the simpler one, i reduced the network to a Req (using Y-Δ transform twice then // and series resistors) I found the 1.5V source current then all voltages nodes. but I am not sure finding the 1.5V source current would help me in this case since i am missing some equations...
     
  11. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Did you obtain a symbolic result, or did you substitute numerical values for the various resistors?

    A symbolic result for your larger network is likely to be VERY large.
     
  12. Nano_Dav

    Thread Starter New Member

    Oct 18, 2013
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    for the simpler one, i used symbolic, not sure how to deal with the bigger one. as maybe you can see i went from a 2 by 2 network to a 3 by 3 network, i would like to know if there is a easy way to analyses these network (script?) and maybe be able to extrapolate to a 4*4 , 5*5 , ...

    btw, thanks for helping, here its 3 am so i m gonna take a nap ... and i ll be back in the morning to catch up,

    Thx,

    David
     
  13. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Your image is a sufficiently blurry that I can't make out all the designators, but using my best guess for them, here is my calculated equivalent input resistance at the node where the 1.5 volts is applied:

    [​IMG]

    Is this anything like what you got?

    Now, for your larger network, the expression for Req is going to be about 100 times larger. Would such an unwieldy thing be of any use to you?

    If you give numerical values for the resistors, then it becomes feasible to solve your large network.

    You said that you want an expression for the voltage across and current through each resistor. If you only have symbolic resistor values, you will end up with 21+21 = 42 absolutely unwieldy expressions.
     
  14. WBahn

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    The simpler one definitely has the advantage of being planar, meaning that it can be redrawn on a sheet of paper without any nodes crossing. That makes setting up mesh current equations very simple.

    The higher-order ones are not planar (or at least I'm pretty sure that they aren't). But that doesn't mean that you can't systematically develop the set of nodal equations.

    But, to come up with a general approach that is scalable, there has to be an identifiable pattern relating how you go from a 2x2 to a 3x3 to a 4x4 and so on. That does not appear to be the case here, or at least it's not obvious that it is.

    If you can come up with a clear description of how you go from an NxN to an (N+1)x(N+1) circuit, we can help you turn that into a set of equations that use a coherent indexing scheme.

    It appears that such a scheme would be a three-dimensional set of nodes with nodes of the form Node(x,y,z) where x and y each run from 0 to N (so one more node than there are supplies on each edge) and z is either 0 or 1 (either the "lower" vertical plane or the "upper" horizontal plane).
     
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