R1 + R2 Ratios

[TETPV]

Hi


Quick Question about calculations, if we have a ratio between 2.5mm cable and 1.5 mm cable how can i calculate either R1 or R2 from a (R1+R2) value.

if i use a common denomenator method i.e. 5 / 8 where 0.5 is the greatest denominator then x 3 for 1.5 mm and x5 for 2.5 then the resistance of the cpc (1.5) is much lower than that of R1 but given the CSA of the 2.5 is larger i'd expect that value to be higher

hope this makes sense

 

[telectrix]

don't make sense to me. the ratio for 2.5/1.5 is 1.67. i.e. R2=(R1x1.67). for other ratios, the value of R2 is determined by the ratio of the csa of each conductor.

 

[malcolmsanford]

To be honest Hi Ho it does not make a lot of of sense to be honest.

The ratio between 2.5 and 1.5 mm cable is 2.5/1.5= 1.67. Therefore your 1.5mm cable will have a greater impedance as the CSA is smaller. An example would be a 2,5mm of 0.54 ohm, the same length of cable in 1.5mm would be 0.54*1.67 = 0.90 (rounded)

 

[alli]

If you devide 2.5 by 1.5 you get a factor of 1.67

Therefore if your 2.5mm cable measured 0.03 Ohms, I would therefore expect 1.5mm cable to have 1.67 times more resistance (0.03 x 1.67) = 0.05 Ohms

I hope this is the question you asked.

 

[tony mc]

Is this what your after Hi Ho

Courtesy of Widdler copied from a previous post hope it helps!!

RT represents the total, in this case, the R1&R2.

A1 is the CSA of R1, and A2 is the CSA of R2.

For example... say you have an R1&R2 of 0.85ohms and you want to determine R1, Rn and R2. In theory we can determine Rn from obtaining R1's value.

So..

R1&R2 = 0.85 ohms..

R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5) = 0.53 ohms

R1 = (RTXA2)/(A1+A2) = (0.85x1.5)/(2.5+1.5) = 0.32 ohms

So we have (R1) 0.32 ohms + (R2) 0.53 ohms = 0.85 ohms (R1&R2)

 

[TETPV]

Hi


Thats exactly it, my apologies if my description is poor


Thanks

 

[Geoffsd]

then x 3 for 1.5 mm and x5 for 2.5 then the resistance of the cpc (1.5) is much lower than that of R1 but given the CSA of the 2.5 is larger

It works out the other way round - swap the multipliers.

x3 for the 2.5 and
x5 for the cpc.

e.g. R1=R2 = 0.8

0.8 / 8 = 0.1

therefore R1 = 0.1 x 3 = 0.3 and
R2 = 0.1 x 5 = 0.5

 

[Sparky Ninja]

I think tony mc has explained it in the best possible way.


:goofy:

 

[Deleted member 26818]

I add together the two CSAs, divide the R1 + R2 by the total, and then multiply that by the CSA of the other conductor to the one I wish to determine.
Using Tony's value of 0.85.
2.5 + 1.5 = 4
0.85 / 4 = 0.2125
0.2125 X 1.5 = 0.31875 = R2
0.2125 X 2.5 = 0.53125 = R1.

 

[JUD]

I add together the two CSAs, divide the R1 + R2 by the total, and then multiply that by the CSA of the other conductor to the one I wish to determine.
Using Tony's value of 0.85.
2.5 + 1.5 = 4
0.85 / 4 = 0.2125
0.2125 X 1.5 = 0.31875 = R2
0.2125 X 2.5 = 0.53125 = R1.

I think that's the way tony mc has explained it. :shades_smile:

I add together the two CSAs -- R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5)

divide the R1 + R2 by the total -- R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5)

and then multiply that by the CSA of the other conductor to the one I wish to determine -- R2 = (RTXA1)/(A1+A2) = (0.85x2.5)/(2.5+1.5)

 

[Deleted member 26818]

I think that's the way tony mc has explained it. :shades_smile:

Too many brackets in Tony's version for me.
Usually when I see that many brackets, I go away and have a cup of tea and a smoke, then get on with something else.

 

[telectrix]

I add together the two CSAs, divide the R1 + R2 by the total, and then multiply that by the CSA of the other conductor to the one I wish to determine.
Using Tony's value of 0.85.
2.5 + 1.5 = 4
0.85 / 4 = 0.2125
0.2125 X 1.5 = 0.31875 = R2
0.2125 X 2.5 = 0.53125 = R1.

something amiss there, you get R1>R2.

my way:-

R1+R2=0.85
R1+ (R1x 1.67) = 0.85
R1 x (2.67) = 0.85
R1 = 0.85/2.67 = 0.318
R2 = 0.85 - 0.318 = 0.532

 

[JUD]

something amiss there, you get R1>R2.

my way:-

R1+R2=0.85
R1+ (R1x 1.67) = 0.85
R1 x (2.67) = 0.85
R1 = 0.85/2.67 = 0.318
R2 = 0.85 - 0.318 = 0.532

I think he just mixed it up.

Should be....

0.2125 X 1.5 = 0.31875 = R1
0.2125 X 2.5 = 0.53125 = R2.

 

[Geoffsd]

I add together the two CSAs, divide the R1 + R2 by the total, and then multiply that by the CSA of the other conductor to the one I wish to determine.
Using Tony's value of 0.85.
2.5 + 1.5 = 4
0.85 / 4 = 0.2125
0.2125 X 1.5 = 0.31875 = R1
0.2125 X 2.5 = 0.53125 = R2.

Only a misprint

 

[Geoffsd]

Too slow again