In a universal motor, the most common cause of brush sparking is

In a universal motor, the most common cause of brush sparking is

Right Answer is:

All of the above

6 Signs of a Bad or Burnt Car Valves

SOLUTION

The carbon brush is a crucial piece to keep machines operating efficiently. One common problem is sparking at the brush face, which is usually the first symptom of trouble elsewhere.

Following is a brief rundown of the more common causes of sparking

High commutator mica

If the commutator has high mica or fins of mica that reach up to the brush surface, vibration and sparking may result. Similarly, any burrs of copper left as a result of the undercutting operation will cause trouble. In some locations and atmospheres, commutator slots may become filled with foreign material. This can cause the brushes to vibrate or cause ring fire by permitting current to leak through from one bar to the other.

Open Armature Winding

An open circuit in an armature coil causes “the most vicious form of sparking, which is always accompanied by severe pitting of the mica between the commutator bars connected to this coil and the adjacent coil. The armature must be kept clean to ensure proper balance. Unbalance in the set will pound out the bearings and wear the bearing housing oversize.

Shorted Armature Winding

Shorted armature winding causes excessive arching, lower speed, and loss of power. A short circuit between two sections of a coil, two coils in the same slot, end connections of two coils, or between the commutator bars, will be evidenced by excessive heating of the coils affected, and unless repaired will sooner or later result in a burned-out coil. Blow out the armature regularly with clean, dry compressed air. Clean out the inside of the armature thoroughly by attaching a long pipe to the compressed air line and reaching into the armature coils.

Brush Holders not equally spaced

This condition may appear as unequal sparking on different holders. It can be determined by counting the number of bars between holders or by putting a band of paper around the commutator, marking the positions of the brush toes, removing the paper, and measuring the distance marks.

Brush Holders damaged or dirty

Any physical damage to the holder or an accumulation of dirt on its inside may interfere with the free movement of the brush in the holder and thus result in sparking. Since the commutator is seldom perfectly round or concentric, the brush must move in and out of its holder in order to maintain effective contact.

Overloads

Excessive overloads may result in severe sparking, especially if the interpoles have passed their saturation point and are, therefore, unable to increase their strength as required. If the machine has an ammeter, compare its load with the nameplate rating.

Troubleshooting Universal, Series, Shunt, or Compound DC Motor

Trouble Problem cause
Will not start Open circuit in connection to the line.

Open circuit in the motor winding.

Worn brushes and/or annealed brush springs.

Open circuit or short circuit in the armature winding.

Starts, but heats rapidly Winding short-circuited or grounded.
Starts, but runs too hot. Winding short-circuited or grounded.
Sluggish; sparks severely at the brushes High mica between commutator bars.

Dirty commutator or commutator is out of round.

Worn brushes or annealed brush springs.

Open circuit or short circuit in the armature winding.

Oil-soaked brushes.

Abnormally high speed; sparks severely at the brushes. Open circuit in the shunt winding.
Reduction in power; motor gets too hot Open circuit or short circuit in the armature windings.

Sticky or tight bearings.

Interference between the stationary and rotating members.

Motor blows fuse or does not stop when the switch is turned to OFF position. Grounded near switch end of the winding.

Shorted or grounded armature winding.

Jerky operation, severe vibration. High mica between commutator bars.

Dirty commutator or commutator is out of found.

Worn brushes and/or annealed brush springs. Open circuit or short circuit in the armature winding.

Shorted or grounded armature winding.

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