# Electronics LEDs

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

1. ### benji2412<insert message here>

Joined:
25 Apr 2009
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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. ### TealcNew Member

Joined:
6 Oct 2010
Posts:
129
25
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.

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.

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

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