Causes and inspection methods of spark generated by DC motor

1. Excessive spark caused by motor overload. Can be measured whether the motor current exceeds the rated value, such as the current is too large, then the motor overload.

2. Poor contact between brush and commutator. The reasons are as follows: the surface of the commutator is too dirty; The spring pressure is not suitable, and the spring pressure can be adjusted by spring balance or experience. When replacing the brush, other types of brushes were replaced by mistake. The clearance fit between the brush or brush holder is too tight or too loose. If the fit is too tight, emery cloth can be used to grind. If the contact surface is too small or the brush direction is reversed, the contact surface is too small is mainly caused by improper grinding method when replacing the brush. The correct grinding method is to use N320 fine emery cloth to press between the brush and the commutator (the side with sand faces the brush and is close to the surface of the commutator. The emery cloth cannot be straightened), and the emery cloth moves along the working direction of the motor.

3. The brush holder is loose and the brush arrangement is not in a straight line. The greater the brush position deviation, the greater the spark.

4. Excessive spark caused by armature vibration. The reasons are as follows: the gap between the armature and the magnetic poles is uneven, resulting in different voltages in each branch of the armature winding, and the current generated inside causes the brush to generate sparks; bearing wear causes the upper gap between the armature and the magnetic pole to be too large, and the lower gap Small; the axis of the coupling is incorrect; the belt of the motor driven by the belt is too tight.

5. Short circuit between commutating segments. The reasons are as follows: brush powder and commutator copper powder are filled in the grooves of the commutator; Mica corrosion between commutator segments; The brush formed when repairing the commutator was not eliminated in time.

6. The position of the brush is not at the neutral point. The reasons are as follows: the improper movement of the brush position or the loosening of the fixing bolts of the brush holder during the repair process, resulting in excessive sparks under the brush.

7. Reversing connection of commutating pole winding. The method of judgment is to take out the armature and pass low-voltage direct current to the stator. Use a small magnetic needle to test the polarity of the reversing pole. Along the direction of motor rotation, the generator is "n-N-S-S" and the motor is "n-S-s-N" (where uppercase letters are the main pole polarity and lowercase letters are the reversing pole polarity).

8. The commutation pole magnetic field is too strong or too weak. If the commutation pole magnetic field is too strong, the following symptoms will appear: green needle sparks, the sparks are located at the sliding end of the brush and commutator, and the surface of the commutator is symmetrically burned. For generators, the brushes can be moved by an appropriate angle against the direction of rotation; for motors, the brushes can be moved by an appropriate angle in the direction of rotation.

If the commutating pole field is too weak, the following symptoms will occur: the spark is located at the sliding end of the brush and commutator. For generators, the brushes need to be moved by an appropriate angle in the direction of rotation; for motors, the brushes need to be moved by an appropriate angle against the direction of rotation.

9. The commutator is eccentric. In addition to manufacturing reasons, it is mainly caused by improper repair methods. The reason for the mica protrusion between the commutator segments is that when the commutator slot is dug and cut, the edge mica segments are not cleaned, and when the commutator segments are worn, the mica segments protrude, causing flashover.

10. Armature winding and commutator desoldering. Use a multimeter (or bridge) to measure the resistance of two adjacent pieces one by one. If the resistance between a certain two pieces is greater than that of any other two pieces, it indicates that the winding between the two pieces has been desoldered or broken.