5K40.40 Motor/Generator

Concepts

Electromagnetic induction, conservation of energy, Faraday's law, motors and generators, DC and AC signal generation

Overview

This device can be used as a hand-cranked generator or as a DC motor.

A loop of wire placed between two permanent magnets spins when the handle is rotated. This results in a change of magnetic flux through the area enclosed by the loop with time, generating an EMF. In DC configuration, the galvanometer will deflect in only one direction, depending on the direction of rotation. When AC connections are made, the galvanometer will alternate between positive and negative values.

In motor mode, this device needs to be connected to a DC power supply.

Details

Equipment

  • [1] CENCO motor/generator
  • [4] Metal brushes
  • [1] Galvanometer
  • [2] Banana cable
  • [1] DC power supply (large current)

Classroom Assembly

Generator mode

  1. Disconnect the DC power supply, if applicable.
  2. Connect the motor/generator to the galvanometer using banana cables.
  3. Place the meter under the document camera.

Motor mode

  1. Disconnect the galvanometer, if applicable.
  2. Connect the motor/generator to the DC power supply using banana cables.

Important Notes

  • Do not run the motor/generator as a motor for extended periods of time.
  • If the motor does not turn when a large current is going through, turn off the current.

Script

Generator mode

  1. Make DC connections by placing two metal brushes on opposite sides of the split-ring commutator.
  2. Rotate the handle and observe the galvanometer.
  3. Change the metal brushes to AC configuration, contacting the two continuous rings as shown in the picture.
  4. Rotate the handle and observe the galvanometer.
  5. Wiggle the coil back and forth at the positions of maximum flux through the coil (smallest generated voltage) and minimum flux (largest generated voltage).

Motor mode

  1. Make DC connections by placing two metal brushes on opposite sides of the split-ring commutator.
  2. Turn up the current and get the motor started with a light spin. At maximum current and V ~ 5 V, it should turn quite quickly.
  3. Turn off the DC power supply.

 

Additional Resources

References

  • PIRA 5K40.40

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2018

Technicals

This thing originally came with some kind of electromagnet which disappeared years ago. Jeff Rudd stuck a couple of permanent magnets on it.

The motor/generator needs occasional maintenance to work in motor mode. The bearings need wiping and oiling; 3-in-1 oil works well. The brushes and contact rings need to have oxides stripped off; Scotch-Brite works well. The brushes should lightly touch the contact ring(s) without producing so much friction that the motor stalls.

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.