AC Generators

These STEAM experiments are thinking to teach our kids (maybe 7th or 8th Grade) AC generators basics, building these easy experiments at classroom.

These experiments will allow us to review concepts such as:

• Ohm´s law
• Electromagnetic induction basics
• AC generator basics
• Shape wave captured by an oscilloscope
• Half wave rectifier
• AC/DC conversion
• RC circuits design
• Signal filtering

At the end of this instructable I propose several challenges to build at classroom.

I hope you like.

• Cork
• Acetate sheet
• Wooden rods
• 20 countersunk hole magnets (10 X 2 mm)
• 1,2 mm and 3,3 mm enameled cooper wire (100 meters at least)
• Osciloscope
• Leds
• Diode
• 1 microfarad and 10 microfarad capacitors
• Plastic lid

The goal of the experiment is to generate more than 4,5 V (Vp), building the following generator:

1. Using the acetate sheet to build a cylinder: 2,5 centimeters diameter (first image)
2. Build a coil (cupper wire 0,15 mm) with al least 1700 turns and 3 centimeters long (first image)
3. Glue four pieces of cardboard (second image)
4. Glue two wooden rods to the pieces of cardorad (third image)
5. Open a centered hole to the plastic lid (fourth image)
6. Stick several magnets in the white cork (fifth image)
7. Stick the rods in the white cork centered in the magnets
8. Place the center rod through the plastic lid with several magnets in repulsion with the magnets in the cork
9. These 11 magnets will levitate over the magnets in the cork

To observe the results, I have used several yellows and red leds soldered over two metal rods. The yellow leds have been soldered with its positive terminal at the right side and the red ones with its positive terminal in the left side.

Using the oscilloscope we can study the wave shape generated by the experiment.

We can observe how the voltage generated is related with the velocity of the magnets

To make a half wave rectifier I have used one diode. It will depend where you place the diode to rectifier the positive or negative values of the wave. In that way you will convert AC to DC.

The goal of this second experiment is to generate more than 4,5 V (Vp) building the following generator:

1. Using the acetate paper to build a cylinder: 4 centimeters diameter (first image)
2. Open two holes in the cylinder to pass through it a wooden rod (first image)
3. Build a coil (cupper wire 0,33 mm) with al least 400 turns and 3 centimeters long (first image)
4. Break a magnet and use several pieces of magnets to adjust a wooden rod (second and third images)
5. Use 11 magnets as you can see in the third image

To observe the results, I have used the same metal rods with leds used in the previous experiment.

In the image we can see the wave form generated and the position of the magnets while they go from the position #1 to #2 (where the value increases) and from the position #2 to the #3 (where the value decreases)

As in the first experiment, I have used one diode to rectifier the wave.

In this experiment I have used one diode and one microfarad capacitor to filter the rectified wave.

You can oberve how the capacitor charge to a level voltage and how it discharges following the typical shape waveform of a RC circuit.

You can change the value of the capacitor and observe how the waveform changes.

We can use the generator #2 to mount a simple RC circuit to light off two leds.

Using the time constant calculator from here we can design the circuit to maintain the leds on.

This time I have used R = 3000 ohms and C = 2000 microfarad, so the lights will be on at least during 6 seconds as you can see in the video.

You can propose your students to design RC circuits to maintain the leds on during a specified period of time.

Others experiments we can build modifying the second generator are the following:

• Rotate the magnets placing a gear wheel in the wooden rod and using a motor with other gear wheel
• Change the gear ratio between the gear wheels and measure how much the voltage increase or decrease
• Build a wind turbine
• Build a DC generator to light OFF the maximum number of leds.