A bicycle dynamo works by converting the mechanical motion of the rotating wheel into electrical motion with the use of a magnet. The dynamo contains a permanent magnet wound with coils of insulated wire. When the magnet rotates, it creates a changing magnetic field, which generates electricity in the wire.
A bicycle dynamo is a type of generator attached to a bicycle to produce electricity for the bicycle’s lights. The top of the dynamo touches the tire’s rim, which spins when the bicycle starts moving. Currently, the term dynamo refers to mechanisms that are capable of producing direct current, such as the small devices fitted to bicycles to generate power for the lights.
Typically, a bicycle dynamo has one or more permanent magnets with coils of wire spinning inside their poles. The device consists of a stationary part called a sator and a rotating part called an armature. When the coil spins in the magnetic field created by the magnets, the magnetic flux begins to change trough the coils, resulting in an electric field that generates the charge carriers through the wire. This process produces an electric current. Small bicycle dynamos attain a low efficiency in converting mechanical motion into electricity. However, there are large machines, such as water wheels, that attain high efficiency under ideal conditions.