Gramme machine

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A Gramme machine or Gramme dynamo is kind of electric dynamo named for its Belgian/French inventor, Zénobe Gramme. Gramme demonstrated this apparatus to the Academy of Sciences in Paris in 1871. Unlike the earlier electromagnetic machines, the Gramme machine used a series of thirty armature coils, placed inside a revolving ring of soft iron. The coils are connected in series, and the junction between each pair is connected to a commutator on which two brushes run. The permanent magnets magnetize the soft iron ring, producing a magnetic field which rotates around through the coils in order as the armature turns. This induces a voltage in two of the coils on opposite sides of the armature, which is picked off by the brushes.

With enough coils, the resulting voltage waveform is practically constant, thus producing a near direct current supply. This type of machine needs only electromagnets producing the magnetic field to become a true generator. Supplied with a source of current, the device will act as an electric motor. The innovation of using a ring armature, was an improvement on earlier dynamos and helped usher in development of large-scale electrical devices.

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