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. 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. Earlier electromagnetic machines passed a magnet near the poles of one or two electromagnets, creating brief spikes or pulses of DC resulting in a transient output of low average power, rather than a constant output of high average power.
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 modern generator.
During a demonstration at an inventors' fair in 1873 Gramme accidentally discovered that this device, if supplied with a constant-voltage power supply, will act as an electric motor. The Gramme Machine was the first powerful electric motor useful as more than a toy or laboratory curiousity. His innovation of using a ring armature, was an improvement on earlier dynamos and helped usher in development of large-scale electrical devices.
