Whisp

06-09-2005, 04:14 PM

Led and Resistor Walkthru

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I wrote this little bit of information to help out. I by no means am an electrical engineer but I have tested this and am not responsible for any damage done to anything you take from this mod walkthru. I also realize there is many other calculators out there but didn't seem to find a walkthru here so posted my old one that I wrote up a long time ago so that people could figure it out on their own.

There is 2 power lines on the computer power supply on the standard molex style cables. That is the 5 volt line which is the red wire and the 12 volt wire which is the yellow.

First off I am going to show a simple equation. The equation to figure out what type of resistor is needed the equation is (power line - led volatge) / led amps. When you buy your led make sure you know the volatage required for it and the amps of it. Some leds might be 10mA while some might be 20mA or can vary.

Anyways now that we have the equation lets apply it.

So lets say we want to put 1 led on a 5 volt line and the led is 3.6 volts and has a milliamp of 20 then this is what that would look like. Also you have to convert the milliamps rating for the equation so devide the milliamps by 1000. For example a 20 Milliamp rating divided by 1000 = 0.02 Amps .

(5 volt[power] - 3.6 volt [led]) / 0.02 amps [ 20 mA]

= 70

So now we know you need a resistor that is 70 ohms

If this was a 12 volt line it would then be:

(12 volt[power] - 3.6 volt [led]) / 0.02 amps [ 20 mA]

= 420

So on the 12 volt rail you need a 420 ohm resistor.

Anyways that is the basics.

If you want to add more then 1 led then you times the volts of the LED by the number of LED's and use that number in your equation.

--------------------

This would be for putting them in series.

Example:

two 3.6 leds with a mA of 20 would be 7.2 volts and you would still be at 20mA so the equation looks like this.

(12volt[power] - 7.2 volt [led's]) / 0.02 amps [20 mA]

= 240

--------------------

This would be the equation for parallel.

Example:

three 3.6 leds with a mA of 20 on a 5 volt rail.

In parallel you multiply the mA by the number of Led's you want to use so since we want 3 leds it would be a mA of 60.

(5 volt[power] - 3.6[led]) / 0.06 amps [60 mA]

= 23

--------------------

The end results for the resistors won't be exact on with what you can buy so you need to find the closest one. As I mentioned I am not an eletrical engeneer so some of that might be a bit off but I have used these calculations many times in my mods and have not had an issue or anything blow up yet.

__________________________________________________ __________________________________________________ _________________________

I wrote this little bit of information to help out. I by no means am an electrical engineer but I have tested this and am not responsible for any damage done to anything you take from this mod walkthru. I also realize there is many other calculators out there but didn't seem to find a walkthru here so posted my old one that I wrote up a long time ago so that people could figure it out on their own.

There is 2 power lines on the computer power supply on the standard molex style cables. That is the 5 volt line which is the red wire and the 12 volt wire which is the yellow.

First off I am going to show a simple equation. The equation to figure out what type of resistor is needed the equation is (power line - led volatge) / led amps. When you buy your led make sure you know the volatage required for it and the amps of it. Some leds might be 10mA while some might be 20mA or can vary.

Anyways now that we have the equation lets apply it.

So lets say we want to put 1 led on a 5 volt line and the led is 3.6 volts and has a milliamp of 20 then this is what that would look like. Also you have to convert the milliamps rating for the equation so devide the milliamps by 1000. For example a 20 Milliamp rating divided by 1000 = 0.02 Amps .

(5 volt[power] - 3.6 volt [led]) / 0.02 amps [ 20 mA]

= 70

So now we know you need a resistor that is 70 ohms

If this was a 12 volt line it would then be:

(12 volt[power] - 3.6 volt [led]) / 0.02 amps [ 20 mA]

= 420

So on the 12 volt rail you need a 420 ohm resistor.

Anyways that is the basics.

If you want to add more then 1 led then you times the volts of the LED by the number of LED's and use that number in your equation.

--------------------

This would be for putting them in series.

Example:

two 3.6 leds with a mA of 20 would be 7.2 volts and you would still be at 20mA so the equation looks like this.

(12volt[power] - 7.2 volt [led's]) / 0.02 amps [20 mA]

= 240

--------------------

This would be the equation for parallel.

Example:

three 3.6 leds with a mA of 20 on a 5 volt rail.

In parallel you multiply the mA by the number of Led's you want to use so since we want 3 leds it would be a mA of 60.

(5 volt[power] - 3.6[led]) / 0.06 amps [60 mA]

= 23

--------------------

The end results for the resistors won't be exact on with what you can buy so you need to find the closest one. As I mentioned I am not an eletrical engeneer so some of that might be a bit off but I have used these calculations many times in my mods and have not had an issue or anything blow up yet.