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What causes sparks in high-power DC motors? How to check?

2019-11-07 11:00:00

The causes and inspection methods of sparks generated by high-power DC motors are as follows:
(1) Motor overload When it is judged that the excessive spark caused by the overload of the motor, it can be measured whether the motor current exceeds the rated value. If the current is too large, the motor is overloaded.
(2) Poor contact between the brush and the commutator a. The surface of the commutator is too dirty.
b. The spring pressure is not suitable. Spring pressure can be adjusted with a spring scale or empirically.
c. When replacing the brush, the brush of the actual model was replaced by mistake.
d. The clearance between the brush and the brush grip is too tight or too loose. The fit is too tight and can be ground with abrasive cloth. If the fit is too loose, the brushes need to be replaced.
e. The contact surface is too small or the brush direction is reversed. The contact surface is too small mainly due to improper grinding method when replacing the brush. The correct method is to use a fine abrasive cloth of 00 size between the brush and the commutator (the sandy side is facing the brush, and it is close to the surface of the commutator, and the sand is not straight). The motor works to move.
(3) The brush holder is loose, and the brushes are not aligned. If the high-power DC motor is not linear during operation, it will affect the commutation. The larger the brush position deviation, the larger the spark.
(4) The armature vibration causes excessive spark a, the gap between the armature and the magnetic poles is uneven, causing the voltages in the branches of the armature winding to be different, and the equalizing current generated in the armature causes the brush to spark.
b. Bearing abrasion causes the gap between the armature and the upper part of the magnetic field pole to be too large, and the gap between the lower part to be small.
c. Coupling (also called pair wheel). The axis was not found correctly.
d. The belt-driven motor is too tight.
(5) Short circuit a between commutator segments, brush powder, commutator copper powder filled in commutator groove b, short circuit between commutator segments c, and brush formation during repair of commutator, which was not cleared in time.
(6) The position of the brush is not on the neutral line: due to improper movement or loose brush bolts during repair, the brush spark is too large, and the neutral point must be readjusted. The method is a. Direct adjustment method: first loosen the bolts of the fixed brush holder, put on insulating gloves, tighten the brush holder with both hands, then drive the car, and turn the brush holder slowly by hand with the motor rotating direction. If the spark increases or does not change, you can change the direction nonsense and rotate until the spark is minimum.
b. Induction method: When the armature is stationary, connect the millivolt meter to two adjacent sets of brushes (brushes must be in good contact with the commutator), and the field winding is connected to a DC power source of 1.5 ~ 3V through switch K. Turn on and off the circuit of the rough magnetic winding alternately, the millivolt meter pointer will swing left and right. At this time, move the motor brush holder in the direction of the motor's rotation or in the opposite direction, until the millivolt meter pointer basically does not move, the brush The rack position is at the neutral point.
c. Forward and reverse motor method: For high-power DC motors that allow reverse, first make the motor reverse, then reverse, and adjust the brush position at any time until the forward and reverse speeds are consistent, the position of the brush is the position of the neutral point. .
(7) Reverse pole winding connection: The method of judgment is to take out the armature and the motor passes the following low-voltage direct current. Use a small magnetic needle to test the reversal polarity. Along the direction of motor rotation, the generator is nNzsS, and the motor is nSsN (where uppercase letters are the main pole polarity and lowercase letters are the commutation pole polarity).
(8) The magnetic field of the commutation pole is too strong or too weak. A. The magnetic field of the commutation pole is too weak. The following symptoms will appear: green needle-like sparks: the position of the spark is at the sliding end of the brush and the commutator; the surface of the commutator Symmetric burn. For generators, move the brush an appropriate angle against the direction of rotation. For high-power DC motors, the brush can be moved at an appropriate angle in the direction of rotation.
b. If the magnetic field of the commutation pole is too strong, the following symptoms will occur: the spark position is at the sliding end of the brush and the commutator. For generators, the brushes need to be moved at an appropriate angle in the direction of rotation; for high-power DC motors, the brushes must be moved at an appropriate angle against the direction of rotation.
(9) Eccentricity of commutator: Except for manufacturing reasons, commutator eccentricity is mainly caused by improper repair methods. (10) Mica bumps between commutator discs: Edges of mica discs cannot be removed when the commutator disc groove is cut. Clean. After the reversing sheet wears, the mica sheet will protrude, causing a flashover.
(11) Desoldering the armature winding and commutator: Use a multimeter (or bridge) to measure the resistance of two adjacent commutator pieces one by one. If the resistance between one of the two pieces is greater than the resistance of any other two pieces, This shows that the winding between the two pieces has been desoldered or broken.

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