Crank Radio Dynamo

In the introduction article, we established that a crank radio has a built-in dynamo to generate the electrical power. In this article, we look at what such a dynamo looks like and how it works.

A dynamo converts mechanical energy into electrical energy, and in this case, your muscles produce the mechanical energy by rotating the crank handle. This in turn rotates a magnet, which induces electrical current within a set of fixed coils.

The dynamo is this part, which consists of a metal plate and four screws that secure the module to the plastic case. Removing the screws enables one to gain access to the underside, which houses the gearing mechanism.

In this dynamo design, the coil remains fixed, whilst the permanent magnet drum rotates around it. As you can see, there is a gearing system, which increases the number of rotations of the magnetic drum per rotation of the crank handle. The gearing system therefore provides a mechanical advantage and the dynamo produces more current.

There is a small circuit consisting of four diodes, which forms the full-wave rectifier. This circuit converts the AC current produced by the dynamo to DC so that it may be stored in a rechargeable battery.

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