Hi, I'm looking to change the LEDs in my fans from blue to red, they're decent fans and it's cheaper than buying new fans. Plus it's a chance to get hands on for a bit. I have a 3.16 V going to the current blue LED and I obviously know that 3-5mm red LEDs use a smaller 2.0 V. My question is, how do I calculate what resistor to use? I know there are calculators around but I'd like to do the math myself and have it explained. Reason is I've just joined an Electrical and Electronic Engineering reseach group as a chemist and I think this would be a good way to pick up the basics hands on, as I've done nothing but read about it recently. Thanks, Ben
Good old V= IR that is Voltage = Current x Resistance. You need the circuit to drop an extra 1v at 20mA (LEDs are generally 20mA for ultra bright types) 1v = 0.020A x ? Your fan is probably already resistored up for the more or less a 9v drop from the 12v supply so you are just adding a little extra resistance to it. Wire the resistor to the anode of the new LED and it'll create a series resistor effect. If you are running the fans at lower than 12v then you might want to consider wiring the new LEDs to a permanent 12v source. Here's a couple of guides I made a while back. Colour swap. http://forums.overclockers.co.uk/showthread.php?t=18172549 A More in depth mod with more than 4 LEDs that uses a 12v source rather than fed from the fan input voltage. Result in my Avatar. http://forums.overclockers.co.uk/showthread.php?t=18172810
Thanks for that, was really useful! I was right then needing a 50 Ohm resistor. Just wanted to make sure first, that 12 LED fan looks pretty sweet! I might have a play around with something similar. You'll get the credit too, oh and some rep too!
