Equipment required

The 250 mV dc function of a Simpson 260 or comparable multimeter can be used in place of a dc millivoltmeter.

• dc millivoltmeter (0 to 250 mV deflection) with meter leads
• Low voltage dc supply (6V or 12 V battery, depending on armature size)
• Test leads
• Electrical tape
• Alligator clips
• Plastic tie wraps
• Switch
• Rheostat

Obtain all items listed above and configure the test circuit as shown in the figure at right.

Do NOT connect test leads to the battery at this time.

Designate any bar as bar 1 and mark it with chalk.

Turn the rheostat to the full resistance position and ensure that the switch is in the OFF position.

  Voltage lead ends may be attached to the commutator bars by taping or tie wraps or connected to the risers by alligator clips.

Attach deenergized voltage leads to the commutator bars as described below.

• Simplex lap: Bar 1 and bar directly opposite

• Duplex single reentrant lap: Bars 1 and 2

• Duplex double reentrant lap:
First apply potential to bar 1 and the odd-numbered bar directly opposite. After testing odd bars, apply potential to bar 2 and the even-numbered bar directly opposite.

• Simplex wave: Bar 1 and a bar one pole pitch away that was previously marked

• Duplex single reentrant wave: Bars 1 and 2

• Duplex double reentrant wave: First apply potential to bar 1 and the odd-numbered bar a pole pitch away that was previously marked. After testing the odd-numbered bars, apply potential to bar 2 and the even-numbered bar one pole pitch away that was previously marked.

Number a sheet of paper to correspond to the total number of commutator bars to record your readings.

Attach test leads to the battery terminals.

Turn the switch to the ON position. Slowly turn the rheostat to the midresistance position.

Take sample test readings on bar 1 and adjacent and alternate bars.

Ensure that the reading does not exceed the midscale meter reading. Adjust the rheostat and retest as necessary.

Procedure: Testing simplex lap and wave windings for open and shorted coils

Place one test lead on bar 1 and the other on the adjacent bar (bar 2) in the clockwise direction. Observe and record the reading.

Shift test leads to bar 2 and the adjacent bar (bar 3) in the clockwise direction. Observe and record the reading.

Keep progressing around the commutator the same way. Record all readings obtained, including zero.

A winding ground test will be conducted after completion of the bar-to-bar test for open and shorted coils.

Procedure: Testing simplex lap and wave winding for grounded coils

A ground test will be conducted with the same commutator voltage connection as for open and shorted coils.

If possible, use an alligator clip to attach the test lead to the armature shaft.

Place one lead on bar 1 and the other lead on the armature shaft (ground). Observe and record the readings, including zero.

Move the test lead to bar 2. Record the results, including zero readings.

Progress around the commutator in the same manner until all bars have been read to ground. Record all results obtained, including zero readings.

Turn the rheostat to the full resistance position and turn the switch to the OFF position. Disconnect the test leads from the battery terminals.

Procedure: Testing duplex double reentrant lap and wave windings for open and shorted coils (odd-numbered bars)

Place one test lead on bar 1 and the other on the alternate bar (bar 3) in the clockwise direction. Observe and record the reading.

Shift the test leads to bar 3 and the alternate bar (bar 5) in the clockwise direction. Observe and record the reading.

Progress around the commutator this way. Record all readings obtained.

A ground test will be conducted after completion of a bar-to-bar test on odd-numbered bars for open and shorted coils. Conduct the ground test after testing odd-numbered bars for open and shorted windings and before shifting commutator voltage leads for a bar-to-bar test of even-numbered bars.

Procedure: Testing double reentrant lap and wave windings for grounded coils (odd-numbered bars)

Place one lead on bar 1 and the other lead on armature shaft (ground). Observe and record the readings, including zero.

If possible, attach the test lead to the armature shaft with an alligator clip. Move the test lead to bar 2. Record the results, including zero readings.

Move around the commutator in the same way until all bars have been read to ground. Record all results obtained, including zero readings.

Turn the rheostat to the full resistance position, turn the switch to the OFF position, and disconnect the test leads from the battery terminals.

Procedure: Testing duplex double reentrant lap and wave windings for open, shorted, and grounded coils (even-numbered bars)

Shift voltage leads to the commutator bars previously discussed for duplex double reentrant lap and wave windings. Connect the test leads to battery terminals.

Turn the switch to the ON position and rotate the rheostat to the midresistance position.

Take a sample reading between bars 2 and 4.

Ensure that the reading does not exceed the midscale meter reading. Adjust the rheostat and retest as necessary.

Place one test lead on bar 2 and the other on the alternate bar (bar 4) in the clockwise direction. Observe and record the reading.

Shift the test leads to bar 4 and the alternate bar in a clockwise direction (bar 6).

Progress around the commutator as described. Record all the readings obtained.

Conduct a ground test of coils as described for odd-numbered bars. Record all results obtained, including zero readings.

Turn the rheostat to the full resistance position and turn the switch to the OFF position. Disconnect the leads from the battery terminals.

Typical Circuit Configuration Bar-to-Bar Testing of Armatures