# [SOLVED]How to make register 1/2w value below 1 ohm ? 0.83 / 0.5 /

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#### tong

##### Guest
need tomake 1ohm resistor

I need the value
0.83
0.5
0.38
0.31
( 1% is good )

#### zorro

I'm not sure i've understood the question.
Do you want to obtain these R values?
Can you be more explicit?

T

#### tong

##### Guest
oh! sorry. In my country, I can't buy resister
value below 1 ohm.

Can we build from 2 resisters in paraller?
But I can't make the value below 0.5 ohm

#### gab

##### Junior Member level 1
I had the same problem, years ago ...
Try to find Power Resistors made from a resistive wire that you can solder ...,
and use that wire for buiding new
resitor values.

gab

#### Alexg

##### Member level 2
On 2001-10-30 22:40, tong wrote:
Can we build from 2 resisters in paraller?
But I can't make the value below 0.5 ohm

You can put 3 in parallel and get 0.33 ohm !

Best regards,
Alexg

#### Nasdaq Boom

##### Junior Member level 1
Hi tong,
yes, you can build 1 resistor from 2 or more resisters in parallel. The rules is very simple:
Rp=1/(1/R1+1/R2+...)
where Rp is the resulted parallel resistor and R1, R2, ... are the values of resistor1, resistor2, ...
Hope you help.
Rgds
Nasdaq Boom

<font size=-1>[ This Message was edited by: Nasdaq Boom on 2001-10-31 01:23 ]</font>

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#### sick_man

##### Guest
IT IS SIMPLE

USE SOME WIRE FROM A HEATER ELEMENT

OR USE THE WHOLE DAM ELEMENT

AND RUN A CONTACT ALONG THE LENGHT

SO YOULL GET .000001 OHM TO 220 OHM AT ABOUT 50W - 1 KW

WOOOOOOHAHAHAHAHAHAHAHAHAHAHAHAHHAHA

ZZZZZZZZZZZZZZZZZZ FLASH

IF YOU NEED TO PUT RESISTORS IN PARALLEL

THE CORRECT FORMULAR DEPENDS WHAT RESISORS ARE WHERE

SO IF YOU PUT 1 OHM WITH 1 OHM THIS MAKES .5 AND ALSO A PAIR ADD 1.2 OHM WITH 1.2 OHM THIS MAKES .575

THEN YOU ADD THESE ALL IN PARALLEL YOULL GET .33 OR SO

HANDY VALUE WITH A RESONABLE WATTS HANDELING

ALTERNATIVLY

WHAT I WOULD DO THROUGH MY OWN EXPERIENCE

SOME 20 YEARS IS SIMPLY GET A COPY OF AMBIT INTERNATIONAL

CATALOGUE

THEY STOCK ANY COMPONENT IF ITS NOT LISTED THREE WEEKS MAX THEY WILL HAVE IT WITH YOU

EVEN SOME REALY RARE STUFF LIKE BIG AIR SPACED CAPS FINE SMALL CAPS FOR TUNING XTALS

EVEN XTALS ETC

VERY HANDY

AND RESONABLE
THEY DELIVER TO THE DOOR AND

HAVE DOWN TO .001 OHM SURFACE MOUNT

AND 10 > .01 OHM RANGE IN 10 OF EACH VALUE PAKS
BUT ONLY IN .6 WATTS

THE RANGES FOR 1 WATTS AND ABOVE IT .22 > 1 OHM IN E24

AND 1 >10 IN INTEGERS

{OR AS I DO VISIT THE LOCAL TIP WITH SIX BEERS AND A FEW PAKS OF TOBACCO DISTRIBUTE THESE AND ASK IF YOU CAN RUMAGE AROUND A BIT {TAKE TOOLS }
THEN YOU WILL FROM THAT DAY {LIKE ANY GOOD GUARD DOG IS ONCE BRIBED ONCE TO KEEP THE STILL }
YOU WILL THEN
HAVE A FREE RAIGN TO TAKE WHAT YOU NEED FROM THE CARCUS OF SOCIETY AND REMODULTATE TO A NEW XYZ

{I DESIGNED A MACHINE {USES A MILL LIKE A LAWN MOWER BLADE TO MILL THE TRACKS AND SOLDER OFF }
TO RECLAIM PCB AND COMPONENTS ALSO RECLAIMS LOTS OF METALS ETS SEPARATES THEM{TO AN EXTENT AND BAGS THE COMPONENTS}}

AS LONG AS THE GUYS WORK THERE AND YOU GET WHAT YOU NEED ALL AT ONCE OR SAVE UP TO A TRIP !!!

#### sigint

##### Full Member level 6
Why couldn't you order, (for small quantities ask for sample), from Digikey or Jameco - there are no shipping restrictions on these types of components.

Skip

S

#### sick_man

##### Guest
SAMPLE RESISTORS

LOL :smile:
"WHAT A WONDERFULL PHILOSIPHE YOU HAVE "

#### sigint

##### Full Member level 6
simbox!,

How skeptical are you?, Digikey is happy to sample even the smallest parts - you may have to pay for shipping, but it's worth it - I've been there and done that! - If you work for a large consumer of parts, pretty much anybody will give you what you need for proto's - It's a hell of a lot more practical idea than buying a heater and trying to construct a potentiometer that will fail periodically, the metals used in heating elements oxidize very easily.

Skip

#### sigint

##### Full Member level 6
simbox,

By the way the last half of your edited post makes a hell of a lot more sense than the first.

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#### tong

##### Guest
Thank you all guys.

I think I will parallel 10 items
0.83 = 1.7 // 2 items 1/4w 1%
0.5 = 1 // 2
0.38 = 3.8 // 10
0.31 = 3.1 // 10

or try to request sample from digikey.

#### zorro

Hi tong,

you can use only 2 or 3 Rs, for instance:
(by "//" i mean "in parallel with")

for .83 : 1.2 // 2.7 = 0.8307
for .31 : 1 // 1 // 1.5 // 1.8 = 0.3103
for .38 : 1 // 1 // 1.58 = 0.3798

As a method, take a low value of R (R1) and calculate which one you must put in parallel in order to obtain the desired value:
Rx = 1/(1/Rdesired-1/R1)
If that value is not suited, try with the following greater R1.

Tolerance of the result is the same as that of the components.

Bye

T

#### tong

##### Guest
Oh! very thanx INCA. fantasy..
Do you use any software to trial and error ?

tong,

T

#### tong

##### Guest
By the way, I wrote perl script to calculate
the value. Limit at 1 to 4 resistors. +- 0.0005 ohms.

e:temp> cal.pl 0.3846

the result is
1 0 1.2 1.3 = 0.3842
( I want the 1st resistor is 1 ohm )

<font size=-1>[ This Message was edited by: tong on 2001-10-31 19:57 ]</font>

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#### tong

##### Guest
modified something.

#!/usr/bin/perl

@R=(0,0.5,1,1.1,1.2,1.3,1.5,1.6,1.8,2,2.2,2.4,2.7,3,3.3,3.6,3.9,4.3,4.7,5.1,5.6,6.2,6.8,7.5,8.2,9.1,10,11,12,13,15,16,18,20,22,24,27,30,33,36,39,43,47,51,56,62,68,75);

foreach $R1 (@R) { foreach$R2 (@R)
{
foreach $R3 (@R) { foreach$R4 (@R)
{
if ( $R1 != 0 ) {$X1 = 1/$R1 } else {$X1 = 0 };
if ( $R2 != 0 ) {$X2 = 1/$R2 } else {$X2 = 0 };
if ( $R3 != 0 ) {$X3 = 1/$R3 } else {$X3 = 0 };
if ( $R4 != 0 ) {$X4 = 1/$R4 } else {$X4 = 0 };
next if ( $X1 +$X2 + $X3 +$X4 == 0 );
$RT = 1 / ($X1 + $X2 +$X3 + $X4 );$RT = substr( $RT , 0 , 6 ); print "$R1 $R2$R3 $R4 =$RTn" if ( $RT >=$ARGV[0] and $RT <=$ARGV[0] + 0.0005 );
print "$R1$R2 $R3$R4 = $RTn" if ($RT <= $ARGV[0] and$RT >= \$ARGV[0] - 0.0005 );
}
}
}
}

exit;

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#### tong

##### Guest
I need the value
0.8333
0.5
0.3846
0.3125

the result are

0 1 5.6 47 = 0.8334
0 1 7.5 15 = 0.8333
0 1 10 10 = 0.8333

0 0 1 1 = 0.5

0 1 1.2 1.3 = 0.3842

0 1 0.5 5.1 = 0.3128
1 1 1 5.1 = 0.3128

I need at lease one resistor is 1 ohm in my circuit. Great! ;-0

#### zorro

Hi tong,
good!
answering your question, i didn't use any soft, just the procedure i said. A program as yours is the most suitable.

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#### tong

##### Guest
Digi-key fax me the quotation.
They don't offer free sample ;-0

Anyway, I can built by use 2 cheap resistors.

Thanx all.

<font size=-1>[ This Message was edited by: tong on 2001-11-02 18:31 ]</font>

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