MEPX
Chapter 7 of 10All chapters
  1. 1The simple machines
  2. 2Levers and gears
  3. 3Engines
  4. 4Hydraulics and pneumatics
  5. 5Getting power where it is needed
  6. 6Household machines
  7. 7Electric motors and generators
  8. 8Efficiency and losses
  9. 9Why machines fail
  10. 10Working out an unfamiliar machine

Chapter 7 of 10

Electric motors and generators

One machine, two directions.

How they work

A current in a magnetic field experiences a force, which spins a rotor. Turn the same rotor by hand and it generates current instead. Motor and generator are the same device.

  • Regenerative braking uses the motor as a generator to recover energy.
  • Electric motors reach 90 percent efficiency, far above any combustion engine.

Control

Speed is set by voltage or by switching the supply rapidly. Variable frequency drives are what made electric motors usable everywhere fixed speed used to force mechanical gearing.