# Complex circuit resistance between any two points

Discussion in 'Homework Help' started by guchok, Apr 20, 2011.

1. ### guchok Thread Starter New Member

Apr 20, 2011
1
0
Hallo,

I need asap help, how can I calculate the resistance between any two nodes (mentioned by black circles) on image (http://postimage.org/image/1zdvgoq4k/). In general every single resistance can have different value. And the amount of resistances also can be variable. Is there any analytical known well to do this, or any software, or any theory?
I appreciate any suggestion.

2. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
I can't see any obvious algorithm on the fly, but I 'm quite sure that it has to do with Delta-Wye transformations.
I have lost my appetite for programming quizes for some time now...

3. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,281
326
Is this actually a homework problem?

Whey you say "And the amount of resistances also can be variable.", are all the resistances the same value, but with all of them taking on a single different value for different cases, or do you mean that the value of each individual resistor may be different from all the others?

If all of them can be different, then there will be no shortcut depending on symmetry.

Are you looking for a symbolic solution, where the resistors are given designators such as R1, R2, R3..., and an algebraic expression will be given for the resistance between two poiints? If that is what you are looking for, be aware that in a network like this with 25 nodes, such an expression would take a ream of paper to print out! It would be completely impractical to derive a symbolic expression. However, it can be done with the aid of modern mathematical software.

On the other hand, if a numeric value is all you need, that is much more reasonable to do, and I can show you how to do it.

If you want to do it, please make some additions to your schematic. Label the resistors with designators R1 through R40. You will need to pick a node as the reference node; I suggest the bottom middle node. Show it grounded, number the rest of the nodes 1 through 24, and post this labeled schematic.

I will show you how to set up the admittance matrix, using symbolic designators in the matrix. For a numeric solution, the symbolic designators will be replaced with numeric values, but using symbolics in the matrix will make it easier to see what's going on.