How to make register 1/2w value below 1 ohm ? 0.83 / 0.5 /

EDAboard.com Forum Index -> Professional Hardware and Electronics Design

Author

Message

tong
Guest

30 Oct 2001 19:43

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

zorro

Joined: 06 Sep 2001
Posts: 319
Helped: 34

30 Oct 2001 20:08

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

tong
Guest

30 Oct 2001 23:40

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

Joined: 17 May 2001
Posts: 22

31 Oct 2001 1:34

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

Joined: 14 May 2001
Posts: 51

31 Oct 2001 1:59

Quote:

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

Joined: 09 May 2001
Posts: 20

31 Oct 2001 2:22

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

[ This Message was edited by: Nasdaq Boom on 2001-10-31 01:23 ]

sick_man
Guest

31 Oct 2001 6:22

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

Joined: 01 Jan 1970
Posts: 1010
Helped: 14
Location: State of total confusion

31 Oct 2001 6:35

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

sick_man
Guest

31 Oct 2001 6:36

SAMPLE RESISTORS

LOL Smile

"WHAT A WONDERFULL PHILOSIPHE YOU HAVE "

sigint

Joined: 01 Jan 1970
Posts: 1010
Helped: 14
Location: State of total confusion

31 Oct 2001 9:01

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

Joined: 01 Jan 1970
Posts: 1010
Helped: 14
Location: State of total confusion

31 Oct 2001 9:05

simbox,

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

tong
Guest

31 Oct 2001 14:02

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

Joined: 06 Sep 2001
Posts: 319
Helped: 34

31 Oct 2001 17:37

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

tong
Guest

31 Oct 2001 18:40

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

Maddin

Joined: 26 Sep 2001
Posts: 163
Location: Europe

31 Oct 2001 18:47

tong,

I don't know about your power requirements, but take a look at Caddoc (www.caddoc.com). They offer many different resistors even at your requested range, but don't ask me about pricing and sample availability.

tong
Guest

31 Oct 2001 19:55

I can't visit caddoc.com
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 )

[ This Message was edited by: tong on 2001-10-31 19:57 ]

tong
Guest

31 Oct 2001 20:05

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;

tong
Guest

31 Oct 2001 20:32

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

Joined: 06 Sep 2001
Posts: 319
Helped: 34

31 Oct 2001 21:27

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.

tong
Guest

02 Nov 2001 19:21

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

Anyway, I can built by use 2 cheap resistors.

Thanx all.

[ This Message was edited by: tong on 2001-11-02 18:31 ]

EDAboard.com Forum Index -> Professional Hardware and Electronics Design

Page 1 of 1

All times are GMT + 2 Hours

Abuse
Administrator
Moderators

sitemap