Resistors in Parallel..... tabulated?

kontiki wrote:
kontiki wrote:

Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,


thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...
Click to expand...
It's very simple. Product over difference. For your example, the needed
parallel resistor is
120k * 15.6 k / (120k - 15.6k) = 17.931 k. This is by algebraic
manipulation of the parallel resistance formula.
--
John
 
On Mon, 1 Jan 2007 17:43:21 -0500, "Dorian" <dorianmc@bellsouth.net>
wrote:

"kontiki" <mrphyt2@aol.com> wrote in message
news:1167668555.808466.219960@h40g2000cwb.googlegroups.com...
Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,


Here's an interesting technique for finding parallel resistor values that I
found in a 1961 issue of "Electronics World".



Take the desired resistor value and multiply by any number to get R1. So if
we desire a value of 500 ohms we can multiply 500 ohms by 3 to get our R1
value of 1500 ohms. To get the value of R2 divide the R1 resistor value we
calculated, in this case 1500 ohms, by 1 less than the multiplier number we
used to get R1. Our multiplier number was 3 we will now divide 1500 ohms by
1 less than 3, or 2, to get 750 ohms. These two resistor values 1500 ohms
and 750 ohms will give you the required value of 500 ohms when connected in
parallel. This simple method can be done by most people without a
calculator. This works with any set of multiplier and divider numbers you
choose and the numbers don't have to be whole numbers.



If you need more than two resistor values to get your parallel value you can
still use this method. For example let's say I need a total resistance value
of 25 ohms. I first pick a number that when multiplied by my required
resistance gives me a value I have in stock, in this case I'll pick 6
because 6 x 25 ohms gives me 150 ohms for R1. 150 ohms divided by 5 (1 less
than the multiplier value of 6) gives me 30 ohms for R2. If I don't have a
30 ohm resistor in stock I can take my original divider number and split it
up into two new numbers that add up to the original divider number. In this
case I can use 2 and 3 since they add up to 5. 150 divided by 2 = 75 ohms
and 150 divided by 3 = 50 ohms. If I have these two resistor values I'm
finished. If we do the math we see that 150 ohms in parallel with 50 ohms
and 75 ohms = 25 ohms.



Whether you end up using this method or not it still provides an interesting
insight into the math behind the parallel resistor formula.



Hope at least some of you find this useful or interesting.
Click to expand...
---
Slick! I like it! :)


--
JF
 
kontiki wrote:

kontiki wrote:


Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,



thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...

2 ways.
Click to expand...
You just reverse the standard method..

(120K*15.6K)/(120K-15.6K) = 17.931K which is what you need.

Personally i like this one.
1/(1/15.6K- 1/120k) = 17931;

I can hit the inverse( reciprocal ) key on me calculator at the
end instead of starting it off with a 1/(... , this saves in a 2 key
strokes.









--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
On Mon, 01 Jan 2007 19:48:15 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

kontiki wrote:

kontiki wrote:


Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,



thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...

2 ways.
You just reverse the standard method..

(120K*15.6K)/(120K-15.6K) = 17.931K which is what you need.

Personally i like this one.
1/(1/15.6K- 1/120k) = 17931;

I can hit the inverse( reciprocal ) key on me calculator at the
end instead of starting it off with a 1/(... , this saves in a 2 key
strokes.
Click to expand...
RPN:

15.6
1/x
120
1/x
-
1/x
 
kontiki wrote:
Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
Click to expand...
This may be of use, if you have Matlab- it uses a set of standard
values to find a paralleled resistance within a specified tolerance.
You invoke it by
parallel(neededResistance, tolerance).

It is followed by an almost identical program to find voltage divider
combinations, given a desired ratio and a tolerance.

The final entry in this post is a list of standard ratios for precision
resistors. It can be copied and pasted into the Matlab command window,
and it will save the list to a file, which will be called by the two
programs.
You could easily substitute a list of your own available resistors.
With the given list of resistors, the programs work within one decade;
they could be improved by automatically going up and down a decade, but
that won't matter if you enter a list of the actual resistors you have.
--
John


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Find standard resistor values to get a paralleled resistance.
% Result will be shown as columns with resistance achieved and
% the resistors used.
% Call function with needed resistance and optional tolerance
% (1% will be used if not specified).
function [result] = parallel(neededR, tol)
if (nargin < 2) tol = 0.01; end
load('resistors.mat')
lowlim = 1 - tol;
hilim = 1 + tol;
format compact
p = [0; 0; 0];
L = length(r);
for k = 1 : L
for m = 1 : L
g = r(k) * r(m) / (r(k) + r(m));
if ((g >= lowlim * neededR ) & (g <= hilim * neededR))
p1=[g; r(k); r(m)];
p = [p p1]; % concatenate current value to the result
end
end
end

if (size(p,2)>1)
result = p:),2:size(p,2));
else result = 'no combination found';
end


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Find standard resistor values to get voltage division ratio
% enter ratio as such or as explicit division- e.g, 0.4 or 2/5.
% Result will be shown as columns with ratio achieved and
% the resistors used.
% Call function with needed resistance and optional tolerance
% (1% will be used if not specified).

function [result] = vdivide(ratio, tol)
if (nargin < 2) tol = 0.01;
end
load('resistors.mat') % load up list of resistors
lowlim = 1 - tol;
hilim = 1 + tol;
format compact
p=[0;0;0];
L = length(r);
for k = 1 : L
for m = 1 : L
g = r(k) / (r(k) + r(m));
if ((g >= lowlim * ratio ) & (g <= hilim * ratio))
p1=[g; r(k); r(m)];
p = [p p1]; % concat value found to result
end
end
end
if (size(p,2)>1)
result = p:),2:size(p,2));
else result = 'no combination found';
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
r=[1.0000 1.0200 1.0500 1.0700 1.1000 1.1300 1.1500 1.1800 1.2000...
1.2100 1.2400 1.2700 1.3000 1.3300 1.4000 1.4700 1.5000 1.5400...
1.5800 1.6000 1.6200 1.6500 1.6900 1.7400 1.7800 1.8000 1.8200...
1.8700 1.9100 1.9600 2.0000 2.0500 2.1000 2.1500 2.2000 2.2100...
2.2600 2.3200 2.3700 2.4000 2.4300 2.4700 2.4900 2.5500 2.6100...
2.6700 2.7000 2.7400 2.8000 2.8700 2.9400 3.0000 3.0100 3.0900...
3.1600 3.2400 3.3000 3.3200 3.4000 3.4800 3.5700 3.6000 3.6500...
3.7400 3.8300 3.9000 3.9200 4.0200 4.1200 4.2200 4.3000 4.3200...
4.4200 4.5300 4.6400 4.7000 4.7500 4.8700 4.9900 5.0000 5.1000...
5.2300 5.3600 5.4900 5.6000 5.6200 5.7600 5.9000 6.0400 6.1900...
6.2000 6.3400 6.4900 6.6500 6.8000 6.8100 6.9800 7.1500 7.3200...
7.5000 7.6800 7.8700 8.0600 8.2000 8.2500 8.4500 8.6600 8.8700...
9.0000 9.0900 9.1000 9.3100 9.5300 9.7600 10.0000]
save 'resistors.mat',r;
 
John Larkin wrote:

On Mon, 01 Jan 2007 19:48:15 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


kontiki wrote:


kontiki wrote:



Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,



thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...


2 ways.
You just reverse the standard method..

(120K*15.6K)/(120K-15.6K) = 17.931K which is what you need.

Personally i like this one.
1/(1/15.6K- 1/120k) = 17931;

I can hit the inverse( reciprocal ) key on me calculator at the
end instead of starting it off with a 1/(... , this saves in a 2 key
strokes.


RPN:

15.6
1/x
120
1/x
-
1/x


you guys with your polish calculators. :)
Click to expand...



--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
kontiki wrote:
Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,
Click to expand...
Watch for line wrap in the url below.

http://www.radio-electronics.com/info/circuits/resistors_in_parallel/resistors_in_parallel.php

Ed
 
On Mon, 01 Jan 2007 20:34:10 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Larkin wrote:

On Mon, 01 Jan 2007 19:48:15 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


kontiki wrote:


kontiki wrote:



Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,



thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...


2 ways.
You just reverse the standard method..

(120K*15.6K)/(120K-15.6K) = 17.931K which is what you need.

Personally i like this one.
1/(1/15.6K- 1/120k) = 17931;

I can hit the inverse( reciprocal ) key on me calculator at the
end instead of starting it off with a 1/(... , this saves in a 2 key
strokes.


RPN:

15.6
1/x
120
1/x
-
1/x


you guys with your polish calculators. :)
Click to expand...
Once you learn how to think upside-down, it's hard to break the habit.

John
 
kontiki wrote:

kontiki wrote:


Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,



thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...

So are you saying you are modifying existing circuit?
Click to expand...
With one resistor given, there is only 1 best choice.
Although instinctively I thought of 16K,
18K is the ideal choice, giving 15652 ohms.
Depending on what you are doing, it is not always so critical and 16K might be good enough.

Otherwise I'd start with some even value close to my target( your case 15.6K).
Lets say I have 20K I need to reduce it by 1/4 so something 4-1 = 3 times larger would be 60K
62K is close, if I have 68K I check if it is better after all we are aiming for 15.6 not 15K.
(20*68)/(20+68) = 16.078K

If you don't have mutimeter to check the 2 you instinctively chose, you aren't doing anything critical enough for it to matter , unless you are dealing with small (>500ohm ) resistances.

Most likely, however, I'd first look for double the value, knowing of 33K ( and I happen to know I have bunch of 30K ) , I may pick those two for starters.
 
"kontiki" <mrphyt2@aol.com> wrote in message
news:1167668555.808466.219960@h40g2000cwb.googlegroups.com...
Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,
Click to expand...
Don't know how this link will break up but ...

http://www.amazon.co.uk/Practical-Electronic-Calculations-Formulae-BP/dp/090
0162708/sr=1-1/qid=1167875830/ref=sr_1_1/202-3328544-0989461?ie=UTF8&s=books

has the parallel tables, along with a shedload of other useful basic stuff.
I'd have scanned the pages for you but winXP has junked my perfectly good
scanner .
john







--
Posted via a free Usenet account from http://www.teranews.com
 
Hi, thank you all for your kind replies...(sic.), I'll
"persevere" with the Excel tables (my 12 year-old will relish adding
the embelleshments...).
P.S. for what its worth a "shop assistant" I know well is finishing her
degree (Electrical eng.) this year,some people have to do these fill-in
jobs to make ends meet.
 
kontiki wrote:
Hi, thank you all for your kind replies...(sic.), I'll
"persevere" with the Excel tables (my 12 year-old will relish adding
the embelleshments...).
P.S. for what its worth a "shop assistant" I know well is finishing her
degree (Electrical eng.) this year,some people have to do these fill-in
jobs to make ends meet.
Click to expand...
Hi, Kontiki. Good luck with your little project.

You should be able to do it yourself easily. For the most part,
getting skill in spreadsheets comes down to having something to do, and
learning how to do it. Since every one of your calc cells has the same
equation (Rp = 1/(1/R1 + 1/R2) you can spend your energy in formatting,
learn a trick or two, and balance the prettyprinting effort with the
time you have available. Just look around in the help files and any
tutorials available with the program for advice.

Cheers
Chris
 
kontiki skrev:
kontiki wrote:

Hi, does anyone know where a reference table of parallel resistors
could be found?The table is very useful for quick accurate resultant
resistances (to two places of decimal), the tables I've got are from
Practical Electronics Jan. 1990? and have faded to the point of being
unusable.Most non-standard resistance values are easily ascertained
e.g.for 17 ohms->75//22
quickly and easily!
with thanks,


thank you for your replies....the "math" is fine,....
lets say I want to shunt a 120k res. to get a
15.6k how long does it take to find the required value? a table is much
faster ,and if you are limited by values "at hand" again an alternative
pair is easily/quickly chosen.This is useful for establishing the
practical effects of temperature compensating resistors and
thermistors.
I tend not to fire up the pc each time I need to do the math...
Click to expand...
Very easy:
120k*15.6k / (120k - 15.6k) = 17.93k
 
how do i get the total resistance IN OHMS in parallel if RI,10K,R2 68K AND R3 120K
 
junaidah6162@gmail.com wrote on 11/20/2017 2:30 AM:
> how do i get the total resistance IN OHMS in parallel if RI,10K,R2 68K AND R3 120K

Divide and conquer. First find the resistance of any two in parallel, then
use that value as a single resistor in parallel with the third.

Or... use the generic formula for N resistors in parallel.

1/Rt = 1/R1 + 1/R2 + ... + 1/Rn

Rt = 1 / (1/R1 + 1/R2 + ... + 1/Rn)

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998
 
On Sunday, November 19, 2017 at 11:30:09 PM UTC-8, junaid...@gmail.com wrote:
> how do i get the total resistance IN OHMS in parallel if RI,10K,R2 68K AND R3 120K

Add reciprocals and take the reciprocal of the result. Calculator "1/x" key comes in handy...
 
Congrats. The thread is only ten years old.

Anyway, all you do is add up the reciprocals of the ohms values and then get the reciprocal of that. You can add as many as you want at the same time.

I had to do a bunch of this working on three tube projection TVs. The return resistor of the convergence yokes set the convergence outputs as transconductance amps. The exact value sets the gain.

Different manufacturers use different values, ad sometimes different values in the same set for each off the six channels. We tried to stock all the values all the time but that is about impossible. So I had to make the proper values for the set.

If those values are off the gain is off and you have to realign the whole set of parameters for that channel.

There were six channels but earlier units only had four and used normal geometry correction for the green and applied it to red and blue as well. Some sonys used fixed permanent magnets for this like an old black and white set, after all they were monochrome tubes.

I have a nice strong DS-186B for sale, and a couple of bottles of coolant in case anyone still works on those.
 
On Mon, 20 Nov 2017 09:58:28 -0800 (PST), jurb6006@gmail.com wrote:

Congrats. The thread is only ten years old.

Anyway, all you do is add up the reciprocals of the ohms values and then get the reciprocal of that. You can add as many as you want at the same time.

I had to do a bunch of this working on three tube projection TVs. The return resistor of the convergence yokes set the convergence outputs as transconductance amps. The exact value sets the gain.

Different manufacturers use different values, ad sometimes different values in the same set for each off the six channels. We tried to stock all the values all the time but that is about impossible. So I had to make the proper values for the set.

If those values are off the gain is off and you have to realign the whole set of parameters for that channel.

There were six channels but earlier units only had four and used normal geometry correction for the green and applied it to red and blue as well. Some sonys used fixed permanent magnets for this like an old black and white set, after all they were monochrome tubes.

I have a nice strong DS-186B for sale, and a couple of bottles of coolant in case anyone still works on those.
Click to expand...

People are not buying projectors as much these days, even LCD types
for conference rooms. We're just going to use giant LCD TVs in our
next conference room.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
>"People are not buying projectors as much these days, even LCD types
for conference rooms. We're just going to use giant LCD TVs in our
next conference room. "

I understand why. Less bulk. geometry and convergence are always perfect. there is no real refresh rate so they can handle many different formats without the rigamaroll of the past. (like two or three sets of setup adjustents)

but then the lamps can be problematic. It is a weird system in a way, it looks like it delivers constant watts or something as the voltage requirements of the lamp change with age. Never really looked into it or experimented with it to know for sure.

Another thing is the polarizing filters.

Might I mention that usually the normal failures of a CRT based projection unit were easier to deal with than these things ?

But then that is progress.
 
On 11/20/2017 12:58 PM, jurb6006@gmail.com wrote:
Congrats. The thread is only ten years old.

It's never too late to do the kid's homework for him.
Click to expand...
 
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