Neither parallel nor series

[Wong]

What theorem or method can be applied to calculate the total
resistance at point A to B?

----- A -----
| |
| |
R1 R2
| |
| |
------R3------
| |
| |
R4 R5
| |
| |
----- B -----

Thanks.

 

[burbeck]

hi wong,
kirchoffs law, try
http://math.fullerton.edu/mathews/n2003/KirchoffMod.html

regards

 

[Jack// ani]

What theorem or method can be applied to calculate the total
resistance at point A to B?

----- A -----
| |
| |
R1 R2
| |
| |
------R3------
| |
| |
R4 R5
| |
| |
----- B -----

Thanks.

Star to delta conversion will work here.

Your above star connection can be converted into equivalent delta
connection, like this



RB
___
|--------------|---|___|----------------|
| | | |
| | | |
| | | |
.-. .-.
B RA | | | | RC A
| | | |
| '-' '-' |
| | | |
| ___ | | ___ |
|----|___|-----|-----------|-----|___|--|

R5 R2

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


RA = ( R4*R1 + R1*R3 + R3*R4 ) / R1

RB = ( R4*R1 + R1*R3 + R3*R4 ) / R3

RC = ( R4*R1 + R1*R3 + R3*R4 ) / R4


Now it is easy enough, for you to further simply it.

 

[KM]

Use Delta to STAR conversion,

----- A -----
| | |
| Ra |
R1 | R2
| / \ |
| Rb Rc |
--/----R3----\-
| |
| |
R4 R5
| |
| |
----- B -----

the result became, and it is series with parallel series.

A > | | |

Ra
|
/ \
Rb Rc
--/ \-
| |
| |
R4 R5
| |
| |
----- B -----

Ra = (R1+R2)/(R1+R2+R3)
Rb = (R1+R3)/(R1+R2+R3)
Ra = (R2+R3)/(R1+R2+R3)


it is in Electrical technology by Edward Hughes

KM

 

[Wong]

Use Delta to STAR conversion,



the result became, and it is series with parallel series.

A > | | |


Ra = (R1+R2)/(R1+R2+R3)
Rb = (R1+R3)/(R1+R2+R3)
Ra = (R2+R3)/(R1+R2+R3)


it is in Electrical technology by Edward Hughes

KM

I think there is a correction here, Ra should equal to
(R1*R2)/(R1+R2+R3) and Rb, Rc as well.
So the total resistance is (Ra + ((R4+Rb) || (R5+Rc)))
Let say, R1=1k, R2=2k, R3=3k, R4=4k and R5=5k. I will get the answer
of 2.9k and it is same with my simulation. Thanks !!

 

[Jack// ani]

whoops, what an ugly mistake i did; feeling very shameful.
should be delta to star. really frustrating isn't it……should go and die somewhere.

 

[John Popelish]

whoops, what an ugly mistake i did; feeling very shameful.
should be delta to star. really frustrating isn't it……should go anddie somewhere.

If that is the biggest mistake you make this year, you are doing
better than most of us.

 

[Jack// ani]

die somewhere.

If that is the biggest mistake you make this year,you are doing

well i hope so.

better than most of us.

thanks

 

[William J. Beaty]

What theorem or method can be applied to calculate the total
resistance at point A to B?

----- A -----
| |
| |
R1 R2
| |
| |
------R3------
| |
| |
R4 R5
| |
| |
----- B -----

You forgot to say "I don't like doing my own homework, please
do it for me."


And the correlary: if this ISN'T a homework problem, you
should say so. It also would help if you mentioned what
you've tried so far, and whether you're an absolute beginner
or not.

 

[Bill Bowden]

Use Delta to STAR conversion,



the result became, and it is series with parallel series.

A > | | |


Ra = (R1+R2)/(R1+R2+R3)
Rb = (R1+R3)/(R1+R2+R3)
Ra = (R2+R3)/(R1+R2+R3)

I'm not following these formulas.
If all the resistors R1-R5 are 1 ohm, then the
total resistance from a to b will be 1 ohm.
But, according to the formulas, Ra, Rb ,Rc will
be 2/3 or 0.67 ohms. So, we have 1.67 in parallel
with 1.67 which is 0.83 which is in series with
Ra (0.67). That all adds up to 1.5 ohms, but it
should be 1 ohm.

What am I missing?


-Bill

 

[Don Kelly]

[email protected] (KM) wrote in message

I'm not following these formulas.
If all the resistors R1-R5 are 1 ohm, then the
total resistance from a to b will be 1 ohm.
But, according to the formulas, Ra, Rb ,Rc will
be 2/3 or 0.67 ohms. So, we have 1.67 in parallel
with 1.67 which is 0.83 which is in series with
Ra (0.67). That all adds up to 1.5 ohms, but it
should be 1 ohm.

What am I missing?


-Bill

---------
Nothing:

The formula is wrong for delta to star conversion- try Ra=(R1*R2)/(R1
+R2+R3) etc
This will give you 1 ohm.

In the case where R1/R4 =R2/R5, you can simply remove R3 as it won't have
any effect. (figure out why).

 

[Rich Grise]

---------
Nothing:

The formula is wrong for delta to star conversion- try Ra=(R1*R2)/(R1
+R2+R3) etc
This will give you 1 ohm.

In the case where R1/R4 =R2/R5, you can simply remove R3 as it won't have
any effect. (figure out why).

Because the current's flowing both ways simultaneously, and so, from the
POV of our perceptive systems, cancel each other out and so don't exist.

Cheers!
Rich

 

[John Fields]

Because the current's flowing both ways simultaneously, and so, from the
POV of our perceptive systems, cancel each other out and so don't exist.

---
Puh-leeze...

If R1/R4 = R2/R5, then the voltages at the junctions of R1R4 and R2R5
will be equal, and with no potential difference across R3 current
can't flow through it, whether it's an open, a short, or anything in
between.

As a matter of fact that's why, at null, the detector across a
Wheatstone bridge vanishes.