Use a DC-Powered Fan to Generate Electricity

Objective

The goal of this project is to understand the principles of an electric generator.

Introduction

The circuit boards inside a computer case generate a lot of heat when the computer is turned on. Most computer cases have fans to circulate air through the case so that the circuits do not overheat. Do you know that you can also work backwards and generate electricity by rotating the electric fan? This starter kit will show you how to light an LED by connecting it to DC-powered electric fan.

The fan motor is normally powered by direct current (DC) from the computer's internal power supply. The Bibliography has a reference webpage that shows how an electric generator works (WVIC, 2004).

The fan motor works on the same principle as the generator, but in reverse. Instead of a crank (or turbine) turning to generate electricity, the electricity is flowing through a coil to cause the motor to turn. You'll be proving this for yourself with this project. You will use light-emitting diodes (LEDs) to monitor the voltage produced when the fan is turned by hand.

LEDs are normally powered by a direct current (DC) power source, such as a battery. A DC power source has a constant voltage with a fixed polarity. A diode is a circuit element that only allows current to flow in one direction: the positive (+) lead must be at a more positive potential than the the negative (−) lead. So an LED will only light up when its + lead (customarily the longer of the two leads) is more positive than its − lead. What do you think will happen when you connect the LED to your hand-powered fan generator?

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• electricity,
• direct current (DC),
• light-emitting diode (LED),
• electric generator,
• Ohm's Law.

Questions

• What does it mean to connect electrical components (e.g., two LEDs) in series?
• What does it mean to connect electrical components (e.g., two LEDs) in parallel?

Bibliography

• This webpage has a nice animation that shows how an electric generator works:
  WVIC, 2004. "How an Electric Generator Works," Wisconsin Valley Improvement Company [accessed March 30, 2006] http://www.wvic.com/how-gen-works.htm.
• These pages provide a basic introduction to electricity, both direct current (DC) and alternating current (AC):
  
  • Mackay, D., 1999. "Electricity," http://www.sunblock99.org.uk/sb99/people/DMackay/electricity.html.
  • Mackay, D., 1999. "Direct Current (DC)" http://www.sunblock99.org.uk/sb99/people/DMackay/dc.html.
  • Mackay, D., 1999. "Alternating Current (AC)," http://www.sunblock99.org.uk/sb99/people/DMackay/ac.html.
• These webpages have useful information on LEDs:
  
  • Hewes, J., 2006. "Light Emitting Diodes (LEDs)," The Electronics Club, Kelsey Park Sports College [accessed December 15, 2006] http://www.kpsec.freeuk.com/components/led.htm.
  • Ngineering, 2003. "LED Calculators," Ngineering.com [accessed December 15, 2006] http://www.ngineering.com/LED_Calculators.htm.
• On this page you can build virtual circuits with batteries and resistors, then test your circuit by throwing a switch to light up a bulb. If there's too much current, the virtual light bulb blows up, too little current, and the bulb won't light. When you get the current right, the bulb glows brightly.
  Unknown, 1999. "Ohm's Law." Physics Department, University of Oregon. [accessed December 13, 2006] http://zebu.uoregon.edu/nsf/circuit.html#Ohm

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• a 12 V DC powered computer case fan:
  • Caution: There is so much variation in DC fans that this project is extremely difficult to complete successfully. The DC fan that we have listed below does work, HOWEVER if RadioShack changes their supplier for the fan listed below and replaces the part with a different version of a DC fan, the project might no longer work.
  • Antec 80mm 4-Pin Sleeve Bearing Case Fan, part number 55011227 from Radio Shack (online only, not in stores);
• an LED (light emitting diode), such as:
  • part number 333851 from Jameco Electronics (minimum order is 10, still less than $1; Variations section has ideas for using the extra LEDs);
• alligator clip leads, such as:
  • part number 10444 from Jameco Electronics;
• wire cutter/stripper (needle nose pliers usually have this near the base of the jaws).

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Experimental Procedure

Important safety note: the fan should not be connected to a power source at any time during the experiment!

1. Cut the two lead wires for the fan (leave them as long as you can) and strip the ends.
2. Use two jumper wires to connect the LED to the two stripped lead wires of the fan.
   1. Use one jumper wire for each lead of the LED.
   2. Connect the red wire from the fan to the longer lead (+, anode) of the LED.
   3. Connect the black lead wire from the fan to the shorter lead (−, cathode) of the LED.
3. Use your hand to rotate the fan blades and see what happens.
4. What happens if you rotate the blade faster? Slower? Describe the results in your lab notebook.
5. What happens if you reverse the direction of rotation (counterclockwise instead of clockwise, for example)?

Variations

• What happens if you connect two LEDs to the fan in series? Does the polarity of the connections matter? How?
• If you have a multimeter, use it to measure the voltage drop across the LED and the current flowing through the LED when you spin the fan by hand. Use your results to predict how many LEDs you can light up when connected in series with the fan. Use your results to predict how many LEDs you can light up when connected in parallel with the fan. Here are some inexpensive digital multimeters that would work well for this project:
  • part number BP-1562 from Jameco Electronics, or
  • part number TM-162 from TechBuys.Net, or
  • Radio Shack also has a selection of multimeters, priced slightly higher but you won't have to wait for shipping.
• Use permanent magnets and a coil of wire to make your own generator. The easiest way is to have the magnets spin inside the coil. Use magnet wire #30 gauge or smaller) to make the coil. How do the magnets need to be arranged with respect to the coil to generate current? Is there a relationship between the voltage produced and the number of turns in the coil? Between the current produced and the number of turns in the coil? Is there a relationship between the voltage produced and the rate of spinning the magnets? Between the current produced and the rate of spinning the magnets?

Credits

Franklin Duan,

Edited by Andrew Olson, Ph.D., Science Buddies

Last edit date: 2007-05-10 12:15:00