Lab GA31-19--Loaded Motors & Generators
30 pts.

OEET 120

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Extra Credit (after you've finished, see me to find out how many points you get).

  • Neatly wire up a capacitor-start motor to the experimenter console, using wires with large (yellow) spade terminals on the ends. Have some slack in the wires, but not too much.
  • Mount momentary start/stop buttons and a contactor with a 120 V. coil on the wall, and neatly wire them up.
    • Use 18 AWG wire.
    • For terminals that have clamps to hold wires, use wires without spade terminals.
    • For terminals having just a screw and no clamp, use medium (blue) spade terminals.
    • Connect the start/stop buttons and contactor so that the contactor will remain energized after the start button is released.
      • Like you did for experiment GA22-13, but without a light connected to the contactor.
    • The three heavy-current terminals on each side of the contactor should remain free.
      • They will be used later for turning various pieces of equipment on and off.
    • Provide two long wires that will connect to the 120 VAC terminals on the experimenter console. 
      • Put white tape on the wire connected only to one side of the contactor coil.
      • Put black tape on the wire connected to the start/stop buttons (even if the wire is already black).

 

Experiment Procedure

  1. If a capacitor-start motor hasn't yet been wired up, wire one up as described above and get extra credit.
  2. If start/stop buttons and a contactor haven't already been wired up, do so as described above and get extra credit.
  3. If not already done, connect the shaft of a capacitor-start motor to the shaft of a DC generator.
  4. Unplug the experimenter from the wall, and make sure the 120 VDC supply is off.
  5. Connect the start/stop/contactor assembly to the 120 VAC terminals on the experimenter console.
  6. Connect the top generator armature terminal to one of the high-current contacts on the contactor.
  7. Connect the other side of the high-current contact to the 10 A. input of a meter having a fused 10 A. input.
  8. Connect the black meter input to the top DC motor armature terminal.
  9. Set the meter for measuring 10 A. DC.
  10. Connect the bottom generator armature terminal to the botton DC motor armature terminal.
  11. Use banana-plug leads, etc., to finish wiring up the DC generator and DC motor as you did in experiment GA19-16 (DC Generator & Motor). This wiring is temporary and does not need to be done neatly.
  12. Connect a Prony brake to the shaft of the DC motor, and set it up for no load (slack canvas belt).
  13. Connect an ammeter to measure the DC motor's armature current.
    • Be very sure to use an ammeter with a fused 10 A. terminal, and be sure the red meter lead is plugged into the 10 A. hole.
  14. Have me check everything.
  15. Start up the system using the following procedure:
    • Be sure 120 VDC power supply is off.
    • Turn on capacitor-start motor.
    • Turn on 120 VDC supply and adjust the generator voltage to 100 V.
    • Turn off the 120 VDC supply.
    • Press the start button on the wall.
    • Turn on the 120 VDC supply and, if need be, use a screwdriver to give the DC motor shaft a shove in the clockwise direction to get it going.
      • This won't be necessary once we've built better 120 VDC supplies.
    • Important: If you smell smoke, or if the generator keeps making a loud noise, immediately turn off the 120 VDC supply. 
  16. Tighten up the canvas belt on the Prony brake slightly, until you see the DC motor's armature current increase.
  17. Watch the generator's output voltage decrease as you loosen the Prony brake.
  18. Turn off the system, being sure both the AC switch and the DC power supply switch are in the off position.
  19. Reconnect the ammeter to measure the current going to the capacitor-start motor.
  20. With the Prony brake set for no load, start up the system again.
  21. Tighten the Prony brake, and watch the current of the capacitor-start motor increase.
 
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