Motor Armature testing

When using a ring tester (also known as a shorted turns tester or ringing tester), you are checking the armature windings for internal short circuits. It operates by sending a brief voltage pulse through a coil and measuring the decay or "ringing" of the resulting oscillations.

How a Ring Tester Works

·         Good Coil:

·          A healthy armature winding acts like a ringing bell; the pulse oscillates and takes time to dampen, resulting in multiple "rings" or a high reading on the tester's bar graph.

·         Shorted Coil:

·          If a winding has a shorted turn, it acts as a loaded transformer secondary. This absorbs the energy and causes the ringing to dampen almost immediately, giving you only one or two rings, or dropping the bar graph into the "fault" (red) zone.

Testing Procedure

1.    Set Up:

Place your armature on an external growler or a dedicated winding fixture. Position the ring tester's probe or testing coil directly over the armature winding or slot you are checking.

2.    Read the Output:

Energize the tester and observe the waveform on an Inductor Ring Tester or the LED/bar graph on a dedicated unit.

3.    Compare Coils:

Slowly rotate the armature to test each consecutive winding slot. All healthy coils should yield roughly the same number of rings or display similar readings.

4.    Identify Faults:

If the rings completely disappear or drop drastically on a specific coil, it indicates a shorted turn within that winding section.

Additional Armature Tests

While a ring tester is excellent for detecting shorted turns, proper armature diagnostics require a few additional evaluations. Standard testing generally includes:

·         Bar-to-Bar Resistance Test:

Use a digital multimeter on the lowest ohms setting to check the resistance between adjacent commutator segments. The readings should be nearly identical all the way around the commutator.

·         180-Degree Resistance Test:

Test the resistance of commutator bars exactly 180 degrees apart to ensure winding symmetry.

·         Bar-to-Ground Test:

Check for continuity between the commutator bars and the metal armature shaft. There should be no continuity (infinite resistance) between the segments and the shaft.