@David Johnston posted:You should check the resistance from the commutator segments to the shaft. See if any of the armature coils are grounded. On a large motor the way to find the proper timing of the commutator is to rotate the brush rigging to find the optimum operation. This may be difficult depending on the brush plate design. The field is hard to check without a growler, but the defect might be turn to turn shorts. Reducing the field strength should cause the armature to turn faster, but with less torque. The run out on the commutator can reduce performance, but this problem usually comes with excessive sparking. Allowable runout, bar to bar, is 0.0002” Try increasing and decreasing brush tension and see how that impacts the speed of the armature. Take a look at brush resistance, maybe swap the brushes with a motor that runs well. Excessive bearing clearance can cause a motor to run slow. These little motors need very tight clearance on the armature bearings, maybe 0.001” or less. Good luck.
What should the resistance be between the shaft and segments?
