Generator using a Computer Fan

[originally published by Igor Ramos, Oct 8, 2012, 7:00 PM]

In this tutorial I show how to build an electricity generator using a computer fan.

In the demo below, the steam from my coffee machine is used to drive the computer fan and generated electricity.

The computer fan is a brushless DC fan and has been modified. I'll show you in this tutorial how make that simple modification. I recommend that you read [1], it's a nice background on the topic.

I used a 3 wire 4 coil 80mm fan.

What you need:

1. A computer fan

2. rectifier (one diode + one capacitor)

3. load (one resistor and LED)

Steps

high level summary:

1. Open the fan.

2. Solder a wire in pin 2 and pin 3 of the 4 pin chip. those are your coil outputs

3. take the 2 coil outputs and run through a diode bridge rectifier.

4. hook up you load in the rectifier output.

Detailed instructions:

1. open the fan by removing the c shaped ring. See on references [1] and [2] tips on how to open it. If it's taking you more than 10min to open it, the odds are you have a fan that way too hard to open, I recommending looking for another one. Each fan manufacturer have their own design and some are just way too hard to open

2.

Now that the fan was opened, you want to tap the coil start and end, and tap. I found hard to find the coil start & end, so I found there's a 4-pin component with writing 276. I did a google search for "276 IC" and first result reveals the secret: it's a "UH276, Complementary Outputs Hall Effect Latch Ic". Now I know that the coil Also after some Google research I found the typical wiring diagram of a computer fan - called a brushless DC fan - and it matched closely with that typical application circuit.

Here's the typical application of the UH276:

Based on the typical circuit, we want into the bottom of coil 1 and 2, so go ahead and solder a wire to pin 2 and one to 3 of the IC 276. Those 2 wires you just soldered are is your coil + and coil -.

I did not put the ring back. The magnet had enough force to hold the blades in place.

3. Take the 2 coil wires you just soldered and input into the rectifier. For simplicity a 1/2 wave rectifier is enough. It uses one diode and one capacitor. almost any diode would work (e.g. 1N4148), 10uF. You may experiment with different cap values

4. I used a blue LED with a 100 ohm resistor to limit the current as my load. The activation voltage for the blue LED is higher than the red. So I suggest start with the red

Improvements:

The following are improvements I want to do, but did not have parts on hand.

1. replace diode(1N4148) with Schottky diode.

2. add 3v zener shunt regulator

Other fans:

1. if the fan you have does not look like mine, I suggest doing a google search for the chip on in, and hope you find the datasheet, so that you know where the coil in connected to. The objective is tap into the coil leads an bring to outside the fan

References:

[1] http://pcbheaven.com/wikipages/How_PC_Fans_Work/ retrieved on 10/8/2012

[2] http://www.instructables.com/answers/How-can-I-disassemble-a-dc-brushless-fan-without-b/ retrieved on 10/8/2012

[3] Datasheet for AH276Q http://www.diodes.com/datasheets/AH276Q.pdf

added voltage multiplier to increase output voltage high enough that the LED would turn on.