Wind, water and muscle

Pedal-powered generator

An old bicycle turns a DC motor to light bulbs and shows how much effort electricity takes.

₹500 to 1,000A school afternoonMedium

Jump to the steps
Back wheel off the groundMotor touches tyreBulb lights while you pedal

The big idea

People can make electricity too. Pedalling shows, in your own legs, how much work it takes to produce a single unit.

You will need

Tick things off as you gather them.

Step by step

  1. Lift the back wheel

    Fix the bike on a stand so the back wheel spins freely off the ground. Check it is steady and cannot topple.

  2. Mount the motor

    Fix the motor on a bracket beside the wheel so its shaft presses against the tyre. A spring or rubber band keeps it firmly in contact.

  3. Wire a bulb

    Connect the motor terminals to a 12 volt bulb. Check that all wires are secure and clear of the wheel.

  4. Start pedalling

    One person pedals slowly, then faster. Watch the bulb. Notice how much harder it gets to pedal as the bulb brightens.

  5. Add more bulbs

    Connect a second and third bulb. How does the effort change? How many bulbs can one person light?

  6. Time the effort

    Time how long each person can keep a bulb lit. Compare people.

  7. Work out the effort

    A fit person can sustain about 100 watts. One unit of electricity is 1000 watt hours, so it takes about 10 hours of hard pedalling to make a single unit.

What to look for

  • Pedalling gets harder as you add bulbs.
  • The light goes out the instant you stop. Nothing is stored.
  • Making just one unit takes hours of effort.

Why it works

Your legs turn the wheel, the wheel turns the motor shaft, and the motor, spun by hand, becomes a generator. The harder you pedal, the more electricity you make. When you add bulbs you ask for more electrical power, so you have to put in more muscle power. One electrical unit costs hours of human effort. That is why every unit saved matters.

Try this next

  • Add a battery and a charge controller to store some of the power.
  • Measure the voltage at slow and fast pedalling.
  • Compare with a hand-crank generator.

Stay safe

Make sure the stand is stable. Keep hair and clothes clear of the wheel and chain. Do not connect to mains power or to any inverter.

Link to the grid

The grid does the same job at huge scale. A power plant turns a generator with steam, water or wind instead of legs, and the more power we use, the more fuel or flow it needs.

Learn how the grid works

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