Heavy-Duty DC Motor / Trolley / Subway

Faraday proved an electric motor was possible but, like his many inventions, neither scaled the idea up nor commercialized it. Voltaic piles at that time were the sole source of electricity. Because they produced little electricity high-power motors seemed pointless.


The new field of electricity interested Sprague, a Navy officer. While serving in the Navy, Sprague invented a new type of dynamo generator and installed it on his ship, the USS Lancaster, powering an electric call system.

In 1883, Sprague resigned his Naval commission and joined Edison. He did well working for Edison, especially demonstrating how mathematical modeling can be used in place of some real-world experimentation. This reduced the time and cost of building Edison’s electric plant.

Sprague’s real interest was in electric motors. Noting the large and filthy steam-engines of the day, he imagined a world where heavy-duty electric motors ran everything from streetcars to factories. Edison was the boss and his interest was in lighting, not motors. When Sprague suggested motors, Edison shrugged him off. Rather than arguing, Sprague quit and formed the Sprague Electric Railway & Motor Company.

A New Motor

Sprague quickly innovated two major electrical components. First was a high-power electric motor strong enough to move streetcars or other heavy objects. Second came a regenerative braking system where the brakes act as a generator, returning power back to the grid. The combination enabled streetcars, elevators, subways, and about a century later hybrid cars.

Soon, Sprague’s motors powered streetcars powerful enough to climb the hills of Richmond, Virginia, or pull cables hoisting streetcars up the hills of San Francisco. By 1889, Sprague engines powered 110 “electric railways.” It wouldn’t be long until people realized that, due to no exhaust, the electric trains are suitable for underground use. Tunnels were bored and streets opened to dig out space for underground electric trains.

Sprague also tried convincing long-distance train operators that electricity is a better option than coal but, at the time, the motors were not strong enough. Eventually, a half century later, trains converted from coal to electric motors powered by diesel generators.

Sprague created brush-based DC motors. Eventually, Nicola Tesla would invent the brushless AC motor. However, to this day, the New York City subway and countless others run on DC electricity rather than the easier to manage AC. To this day, Parisian subway trains are referred as “les rames Sprague” (Sprogue trains).