The Electric Self-Starter: Kettering's Motor-Generator

Early cars were started by hand with a crank handle — hard, and dangerous when an engine kicked back. Charles F. Kettering, at the Dayton Engineering Laboratories Company (Delco), filed in 1911 for a system in which one electric machine starts the engine as a motor and then, driven by it, runs as a generator to recharge the battery and power the lights and ignition. Cadillac fitted it from 1912. His specification gives the trick that made a small machine do both jobs: batteries switched *"in series to give twenty-four volts"* for starting, and six volts when the machine runs as a generator. This rung works out the current a starter draws, runs a hobby motor as both motor and generator, and switches a heavy load with a relay the way a starter solenoid does.