Ground Test Open Circuit Test Ground Test. Open Circuit Test A digital multimeter can also be used to test for grounds. Put the Function/Range Switch on the 2M resistance (Ѕ) scale. When the test probes are put on the commutator and the shaft, the meter must give an indication of over load (OL). This means that the resistance is more than 2 megohms. 1. Put the digital multimeter Function / Range Switch on the 200 ohm resistance (Ѕ) scale. 2. Put one test lead on one commutator bar. Put the other test lead on an adjacent (next to) bar and there must be less than one ohm resistance.
This test can also be done with an instrument, such as a Kelvin Double Bridge, that can make a measurement of very low resistance. Do the test the same as above and make a comparison of the resistance measurements. NOTICE Never use air pressure that is more than 205 kPa (30 psi). Make sure the air line has a water filter. If there is an indication of a ground in the above test, remove any dirt or debris form the armature with compressed (pressure) air. Two burned areas on opposite sides of the commutator are indications of an open armature winding. These burned areas can cause very rapid brush wear. Do the test for grounds again.
If there is still an indication of a ground, make a replacement of the armature. Power Train Testing And Adjusting 16