Thomson DC Generator


This model of a direct-current generator was designed by Elihu Thomson to produce a constant voltage. It could also be used as a motor that would maintain a constant speed. It came to the Smithsonian from the U. S. Patent Office, representing patent number 333,573, issued to Thomson on January 5, 1886. The patent itself indicates that no model was submitted (which is not surprising since by that time models were not required), and this example was probably given to the Patent Office at a slightly later date for display purposes.

Thomson and Edwin Houston were school teachers in Philadelphia in the 1870s when they formed a partnership (the Thomson-Houston Company) to enter the new and competitive arc-lighting field. They produced a number of successful generators, motors, meters, and lighting devices. Most of their system employed alternating current, which was as good as direct current for lighting. With the development of the transformer in the mid-1880s, AC systems assumed added importance because electricity generated at a low voltage could now be converted to high voltage for more efficient transmission and then converted back to safer low voltage for use by consumers. But electro-chemical applications (like plating) required DC generators, and, until the invention of a practical AC motor by Nikola Tesla at the end of the 1880s, street railways depended on DC.

Thomson-Houston merged with Edison's company in 1892 to form General Electric.

See US Patent 333573, "Dynamo Electric Machine," issued 5 January 1886 to Elihu Thomson. Claim: "A design with spherical armature and round-type frame to obtain a dynamo-electric machine capable of furnishing a constant potential; or an electric motor capable of maintaining a constant speed." No extant maker's markings. This machine has a revolving circular armature with pulley wheel on one end of shaft and adjustable brushes at the other. Field magnets are supported inside the frame.

Date Made: 1886Patent Date: 1886-01-05

Associated Person: Thomson, ElihuAssociated Company: Thomson-Houston Electric CompanyMaker: Thomson, Elihu

Location: Currently not on view

Place Made: United States: Pennsylvania, Philadelphia

See more items in: Work and Industry: Electricity, Energy & Power


Exhibition Location:

Data Source: National Museum of American History

Id Number: EM.252663Catalog Number: 252663Patent Number: 333573Accession Number: 49064

Object Name: motorelectric motorObject Type: Patent ModelOther Terms: motor; Motors and Generators

Measurements: overall: 6 in x 10 1/2 in x 10 3/4 in; 15.24 cm x 26.67 cm x 27.305 cm


Record Id: nmah_706172

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