Controlled rectifier D-C-D-C 30-hp motor drive

The circuit described uses five silicon-controlled rectifiers (SCR's) in parallel to control the average voltage supplied to a 30-hp (horsepower) series d-c motor. The rectifiers, used in a time-ratio circuit that has a constant pulse width and a variable repetition rate, control the motor speed over a 5-to-1 range, independent of plus or minus 20% changes in input voltage.