Bench Testing: Armature
- Check armature for shorts using a growler. Hold hacksaw blade against armature while slowly rotating armature. A shorted armature will cause hacksaw blade to vibrate when passed over shorted area. Replace as necessary.
- Use a circuit tester to check for grounded armature. Touch one probe to each segment of commutator and other probe to armature core. Continuity should not exist. If continuity exists, replace armature. Use circuit tester to check for open circuit.
- Continuity should exist between each commutator segment. If continuity is not present between each commutator segment, replace armature. Check commutator for outside diameter wear, out-of-round and proper mica insulation depth.
- When correcting out-of-round condition, do not reduce armature size beyond specification. See COMMUTATOR SPECIFICATIONS table. If mica insulation is standing higher than commutator surface, mica insulation must be undercut. See Fig 1.
COMMUTATOR SPECIFICATIONS
| Application | In. (mm) | |
|---|---|---|
| Out-of-Round | ||
| Standard | .0008 (.02) | |
| Limit | .002 (.05) | |
| Outside Diameter | ||
| Standard | 1.18 (30) | |
| Limit | 1.14 (29) | |
| Mica Depth | ||
| Standard | .020-.031 (.5-.8) | |
| Limit | .008 (.2) | |