operate at speeds many times higher than that of any other 60-Hz electric
motor. When operated without load, universal
motors tend to run away, speed being limited only by windage, friction, and commutation. Therefore, large universal
motors are nearly always connected directly to a load to limit speed. On portable tools such as electric saws, the load imposed by the gears, bearings, and cooling
fan is sufficient to hold the no-load speed down to a safe value. With a universal
motor, speed control...
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