Need help with resistor network from hell

[modalenjr]

Does anyone have a math formula to solve this one? (see attachment)

[fivefish]

R4 || R2 || R5 are in parallel. Compute equiv. resistance of these 3 parallel resistors, let's call it R2'.

1/R2' = 1/R2 + 1/R4 + 1/R5 .... solve for R2'

Then do R1 + R2' + R3

[T3sl4co1l]

Does anyone have a math formula to solve this one? (see attachment)

23.3... kohm

Spot the resistors in parallel and use the parallel formula:
1/Req = 1/R1 + 1/R2 + ... + 1/Rn

Then spot the resistors in series and use the addition formula:
Req = R1 + R2 + ... + Rn

Tim

[modalenjr]

Sorry i draw it wrong

[Andy Watson]

Easy! Remove R2. Work-out the resulting network.

Now put R2 back ... if you want - it makes no difference.

[modalenjr]

Easy! Remove R2. Work-out the resulting network.

Now put R2 back ... if you want - it makes no difference.

Don't mind 10K, Every resistor can have a different value.

[wraper]

For easier understanding the same thing drawn differently:

[helius]

In this case the key is that both sides of R2 are equipotential nodes. So no current will ever flow through R2.
It's clearer if drawn this way:

     /--R1--+--R4--\
>----+      R2      +---->
     \__R5__+__R3__/

[Andy Watson]

Don't mind 10K, Every resistor can have a different value.

You didn't mention that!
In that case: Label the ends of R2 as points A and B. Split the network at A and B such that R1, R2 and R5 form an isolated network. Use a delta-star transform on R1, R2 and R5. Now reconnect the star-network to the points A and B.

[T3sl4co1l]

For reducing circuits of this shape, you need nodal analysis (the sledge hammer), or if you prefer a graphical approach, apply delta-wye transformations as mentioned by

In that case: Label the ends of R2 as points A and B. Split the network at A and B such that R1, R2 and R5 form an isolated network. Use a delta-star transform on R1, R2 and R5. Now reconnect the star-network to the points A and B.

Application of this will lead to equations with a lot of R / (R1 + R2 + R3), which after putting things together, probably looks a lot like what blueskull has. (I don't particularly care to check the result for correctness.. )

Tim

[Syntax_Error]

Dave will have a video on nodal analysis, mesh analysis and superposition theorem soon.

In the meantime, you can look at the lectures here:

http://www.digilentinc.com/Classroom/RealAnalog/

Click show all and watch chapter 3 videos and the first video from chapter 4.

[TheUnnamedNewbie]

You can use y-delta tramsform. Use this to turn r1,r2 and r5 intoa y.

[Electric flower]

On first picture you see how to transform delta configuration of resistors into star (or Y)


NOTE: If you had ditched R2 you would still get same result of 20Kohm beacuse all resistors are of the same value, but if they were different you would have to use delta to Y transformation

Side question, if picture is worth thousand words, how much is worth picture of words?

Edit: On the second picture where is correctet exponent on 100 should be 100*10^6, not 100*^5