Back EMF in a series DC motor with large flywheel.

5J10.20 • D+15+12

Back EMF in a series DC motor with large flywheel. The DC motor is series-compound, with a special connection to the inner armature coil to demonstrate 'Back-EMF'. When power is first applied, the 300 watt bulb glows brightly at first, then dims as the motor achieves speed. The 15 watt bulb is off at first, then glows brightly as the motor speeds up, indicating the production of Back-EMF. If a padded stick is pressed down on the spinning flywheel, the 300 watt bulb glows more brightly, and the 15 watt bulb dims. If power to the circuit is cut off, the 15 watt bulb continues to glow, becomming dimmer as motor speed drops, and the 300 watt bulb stays off. Another way to demonstrate Back-EMF is to spin up the motor with a hand-held 'spinner motor' pressed against the flywheel. There is enough residual magnetism in the motor armature to generate a Back-EMF and light the 15 watt bulb.