Figure 7-41.--Checking armature shorts with a growler.
milliammeter with a rheostat and a 6-volt battery, or a
Figure 7-39.--Testing an armature for grounds.
An armature coil internally shorted within itself is
Locating armature grounds (fig. 7-39) may be done
determined with a growler. The growler (figs. 7-41 and
with a test lamp, an ohmmeter, or a growler (if it is
7-42) is plugged into a 120-volt, 60-hertz power supply
equipped with test probes and a meter). You then check
and switched to the ON position. A hacksaw blade is
the dc armature for grounds by placing one probe on the
held parallel to the windings and run across the top of
armature shaft and the other probe on successive bars of
the armature. The armature is continually rotated in the
the commutator until all commutator segments are
growler, and the hacksaw blade test made until the
complete armature has been checked. If a short exists
in the winding below the hacksaw blade, the blade will
Armature opens may be determined with test
equipment having test probes to make commutator
bar-to-bar contact around the armature (fig. 7-40), Test
equipment may be an incandescent lamp with a
low-voltage source, a low-reading ohmmeter, a
Figure 7-42.--External growler construction.
Figure 7-40.--Testing armature coils for an open circuit.