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Electronics LEDs

Discussion in 'Modding' started by benji2412, 22 Nov 2010.

  1. benji2412

    benji2412 <insert message here>

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    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
     
  2. Tealc

    Tealc New Member

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    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
     
    Last edited: 22 Nov 2010
    benji2412 and mvagusta like this.
  3. benji2412

    benji2412 <insert message here>

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    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! :)
     

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