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Bicycle Generator

In this project, students, educators, or hobbyists attach a bicycle to a stand so that one can pedal and the have the rear wheel make a generating dynamo turn. The generator can charge a battery or run lights or other appliances. An inverter connected to the battery can provide alternating current to household devices.

Students have used the bike to power a game console, lights, battery-chargers, radios, pumps, and fans.

It is sometimes necessary to regulate the voltage coming out of the generator to protect some equipment. The voltage is proportional to the rotational speed of the generator; however, when connected to a battery, the voltage can never be much higher than that of the battery, so the battery limits the biker's cadence, no matter how hard the biker is trying to speed up. Students enjoy the tremendous increase in power the battery can take to charge over running a couple lights. To keep from generating too-high voltages, use a single-speed bike or limit a multi-speed bike to low gears.

One 15W compact fluorescent bulb is almost too easy to feel for most bikers. Almost all bikers can sense the effort required to run a 60W incandescent bulb. Competitive cyclists can output 300W for an hour, 800W in sprints. The most anyone has ever output is about 1200W, for a few seconds. Lighter loads are easier to sense when turning the pedals by hand instead of by foot.

EnergyTeachers.org has a complete set-up for demonstrations or experiments for students. Contact us to borrow it or to learn more.

Students learn about power, energy, light, the difference between physical resistance and electrical resistance, alternating and direct current, force, torque, and the capabilities of their body and those of professional athletes.

Depending on their observations and experience and prior knowledge, students may learn the following specific understandings:

*We can know in our bodies what 15, 60, 75, and 150 watts feel like.

*The faster a generator spins, the higher the voltage.

*Compact fluorescent lamps are 4-5 times more efficient than incandescent bulbs, while LEDs are a few times even more.

*Batteries store energy. The power in and the power out are variable.

*Power is the rate of energy transfer per unit time.

*Watts are units of power; Joules are units of energy.

*Electricity is a great way to move useful energy around, including transfers to and from mechanical and light-energy.

*It's possible to calculate the amount of energy or power involved in exercise.

*People in society are thinking about generating electricity with bikes. You can read news articles about gyms with bike generators and consider the claims about the value of the energy generated.

*A bike generator might be good for some household appliances. Students should be able to read a list of household appliances and explain how the bike generator would fare with each.

*Time-series graphs of power make it easy to see how much energy one produces.

*In any system involving the bike generator, there is a sequence of energy transformations a student can describe. To make it easier at first, give the existing transformations out of order and ask the students to put them in the observed order.

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