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DIY Fan LED Mod
Date 1st September 2002
Author Brenton "LINUX" Schulz


Here's a quick guide to making your own LED fan. As always, this is a guide only - perform this mod at your own risk. You'll need:

Tools
Soldering iron, 20-40w or so
Wire cutters/strippers
Drill with 4.5mm bit

Parts
Fan
About 15cm of heat shrink
Solder
4 LEDs of your choosing (1000mcd or more)
About 35cm of hook up wire

First off: power
I decided to take power directly from the fans own power leads. This would reduce me having to have even more wires flapping around my case. in the photo below you can see the resistor coming off the red wire and connecting to the LED and a red wire going off to the right under the electrical tape, that is the negative end of the circuit.

Click to Enlarge

Now, what value resistor?
Well, each of the LEDs I used (DSE cat. Z-4072) have a max continuous forward current of 40mA, and a voltage drop of 1.8v. since there are 4 LEDs i can wire them in series and have a voltage of 7.2v across them. This leaves 4.8v to be dropped by a resistor with about 40mA going through it. To be safe lets calculate it for 30mA, just so the LEDs a bit more in spec.

Now, using ohm's law:
R=E/I
=4.8/0.03
=160

For the wattage:
P=I^2*R
=0.03^2*160
=0.144w

A 1/4 watt resistor will be fine. So, a 160 ohm resistor will do nicely. I used 120 ohm and have 40mA which should be ok and will produce slightly more light, but use 160 if you want to be sure not to blow your LEDs.

For resistor values with LEDs with other voltages here is a quick guide:

Voltage drop = 12v - total of LEDs in series

Voltage DropCurrentResistor (ohms)
1v20mA50
1v40mA25
1v50mA20
2v20mA100
2v40mA50
2v50mA40
3v20mA150
3v40mA75
3v50mA60
4v20mA200
4v40mA130
4v50mA80
5v20mA250
5v40mA170
5v50mA100

If you decide to use 3.5v LEDs 2 resistors will be needed and the LEDs will have to be wired as 2 groups of 2 in series with a 5v drop.


All original content copyright James Rolfe.
All rights reserved. No reproduction allowed without written permission.
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