4 comments on “Replacing Case Fan LEDs

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  2. What about going from Red LED to Blue. i like blue, but the storm scout 2 only comes in red.

    here’s where it gets difficult. the scout 2 has a led switch to turn off the led lights in the fans, but cooler master only makes compatible fans in red and white. so i will have to do your mod to the current fans, rather then just replace them.

    my question is, how do i find out which resistor i will need if i don’t know what voltage stock red ones are? i do not have any testing equipment.

    • *SHAMELESS PLUG* Since I have a new employer, I can pimp my company’s wares. You should be able to get a multimeter for $10-$20. They’re actually pretty useful to have for doing basic computer, house work, projects, etc. You can find one here: https://www.sparkfun.com/products/9141 *END OF SHAMELESS PLUG*

      OK, now for the real answer. From my testing you *likely* don’t need a resistor. The fans I used happen to be current sources, so the value of the resistor did not matter (I put one in to be safe anyway). If you want to be safe, you can put in a resistor.

      Without testing equipment, you can look up the voltage drops across various LEDs: http://en.wikipedia.org/wiki/Light-emitting_diode. You’ll notice that red LEDs generally have a drop of about 1.9V, and blue LEDs have a drop of about 3.3V. This means that you need a higher voltage source to go from red to blue. Whites, on the other hand, have about a 3.3V drop, which means you should be able to just swap directly for a blue, and it should work.

      Once you know your source voltage, your LED voltage, and your current (I generally pick 15mA for most LEDs – just make sure you’re not going over the manufacturer’s limit specified in the datasheet), you can plug these numbers into a resistor calculator like this one: http://led.linear1.org/1led.wiz

      All that being said, if I were you, I would take one of the basic red LED fans you don’t care about and just swap the red LED for a blue LED and see if it works. If it does work (because you’re going from a 1.9V LED to a 3.3V LED), then you know you’re dealing with a current source, and you don’t need to add resistors.

      Hope that helps!

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