T120    09 0217

IB17-26 Motor-Generator Set Using Permanent-Magnet DC Motors
Real Components      10 points
OEET 120

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Many motors can be used as generators. For a motor, we put electrical energy in and get mechanical energy out. For a generator, we put mechanical energy in and get electrical energy out. Permanent-magnet DC motors, and wound-field DC motors both work well as generators.

For this experiment, we'll be using two miniature permanent-magnet DC motors to create a motor-generator set. Connecting a DC motor to a DC geneerator doesn't do us much good, except to demonstrate that motors can be used as generators. However, if we connected an AC motor to a DC generator (or vice versa), we would be accomplishing something useful.

Here's the procedure for this experiment:
  1. Strip a piece of insulation about 1/2 inch long from some 14 AWG wire.
  2. Use the piece of insulation as a tube to connect two of the motors together.
  3. Connect one of the motors in series with a 1 ohm resistor, and connect the serial combination to a power supply. (Be sure to have the power supply voltage turned all the way down to zero.)
  4. Connect the other motor in series with a 1 ohm resistor and a 13 V. light, all in series.
  5. Gradually increase the power supply voltage until the light just glows dimly. 
  6. By measuring voltages across the 1 ohm resistors, you can calculate how much power is being put into the motor, and how much power the generator is putting out. Remember, P = V2/R.
  7. Calculate the efficiency of the whole setup. Efficiency = power from the generator divided by power going into the motor. Express the efficiency as a percentage. Efficiency = _____________

 
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