Ok .. I have some blo0 LEDs I want to hook up to my fanbus. On the LED package, it shows the LEDs being 5v, 30mA. To determine the resistor I need, I used the following formula: Ohm = (Mains Voltage - LED Voltage) / LED Amperes So I'd get (12 - 5) / .03 = 233.333, or rounded to the nearest resistor value (240 I think). I guess the actual question, is 30mA = how many amps? .03 or .003 or what? Thanks, Vert
Usually, LEDs designed for 5V already contain a resistor and are intended to be connected directly to 5V with no resistor needed.
I have some slightly lower rated blue LEDs in my system, and they run on 12V with 470ohm resistors. Remember that the given limits are maxima, so you want to err on the side of caution. The nearest E12 resistor value is 220 ohm, but I'd go for 270 or 330. Better safe than having to buy more expensive blue LEDs.
I looked all over the package the LED came in, and no note about a build in resistor. If you'd like to take a look, go to www.radioshack.com and the part number is 276-311. I dont know if that will tell you anything.
