How to check and repair after DC motor broken?

1. The cause of the fault

(1) The motor does not turn.

When the rotor coil in the motor is broken, the induction line of the motor is broken, the  steady speed device is broken, and the brush is badly worn without contact, the motor will not turn.

In addition, if the motor is subjected to strong vibration or collision, the magnet of the motor stator is broken and stuck in the rotor or the shaft is badly damaged between the shaft and the shaft, and the rotor is stuck. All will cause the motor to not turn. In the event of these two situations, the power shall be cut off immediately, otherwise the rotor coils will be destroyed.

(2)The speed is unstable.

There are many reasons for the instability of motor speed. For example, as the motor runs for a long time, the oil lubricants in the bearing are dried up and the mechanical noise will increase obviously.

If the motor shaft is rotated with the hand, the rotation of the motor will be inflexible; the commutator or brush of the motor is badly worn and the two is not smooth; the sliding sheet of the variable resistance in the electronic speed stabilizing device produces the oxide layer or loosely. There is a bad contact with the resistance chip. The open circuit of the capacitor in the electronic speed circuit will cause the self excited oscillation of the circuit, so that the motor speed appears suddenly and slowly and rhythmlly, and all the above conditions will cause the motor speed instability.

(3) Large electrical noise.

The motor produces large sparks in the process of rotation. If the commutator and brush of the motor are worn seriously, the two is in bad contact, that is, when the rotor is broken in rotation, the spark will be produced. In addition, if the commutator is filled with carbon powder and metal scrap, the contact between the brush and commutator will be poor, resulting in electric sparks.

(4) Turn weak.

The permanent magnet of the stator is vibrated and broken, and some windings in the rotor coil of the motor are open.

2. Repair

(1)The motor bearing is soaked in oil. If the motor speed is unstable, the bearing should be immersed in oil because of its lack of oil.

The concrete methods are: remove the motor, open the outer cover, pry open the motor rear cover, draw out the motor rotor, and use the flat head steel punch with diameter 4mm to wash down the bearing on the motor shell and the rear cover. Then use pure gasoline to wash the bearings, especially to carefully clean the inner bore of bearing.

After washing, dry the bearings and soak them in pure clocks and lubricants for a period of time. When the bearing is immersed in oil, the brush on the commutator and the back cover of the rotor can be cleaned by anhydrous alcohol and finally recovered.

(2) Repair of commutator and brush.

If there is a serious spark, the commutator and brush wear should be checked and repaired.

1)Repair the commutator.

Open the motor housing, pull out the stator, check the wear degree of the commutator and deal with it. If the surface of the commutator is slightly worn, the 3mm wide strip of metallographic paper can be put on the commutator, and the rotor of the motor is rotated to wear the surface until the wear marks disappear. If the surface of the commutator is seriously worn and concave, the bar shaped sandpaper with 4mm wide is set on the commutator, and then the rotor is stuck on the small electric drill. First, the rough grinding is used. When the surface is smooth, the relative position of the brush and the commutator can be adjusted, and the relative position of the electric brush and the commutator can be adjusted to avoid the wear parts.

In addition, some motors are normal in the speed, just producing sparks, interference amplifiers. This phenomenon is likely to be caused by the adhesion of carbon powder and metal powder on the commutator, resulting in bad contact between the brush and the commutator, and can be eliminated by improving the speed method. The specific method is: remove the drive belt on the motor. With a high DC power supply to the motor, the Imin. can be added with the 12~15V voltage if the speed of the motor is converted to an electronic stable motor. The rotation time of the motor can be determined according to the actual conditions, but it can be long and short. The purpose of this method is to use the centrifugal force generated by the motor when rotating at high speed, and throw away the debris on the commutator.

2)Repair the brush.

There are two kinds of brushes in the motor, one carbon brush and the other elastic chip. When the carbon brush is worn, the arc face is closely connected with the commutator, and there is a gap somewhere between them. At this time, a small assorted Rasp File is used to trim the arc surface and be tested on the commutator until the entire arc surface is in close contact with the commutator. In addition, a rubber block is attached to the back of the carbon brush rack, which strengthens the elasticity of the brush. In use, if the rubber block is dropped or partially opened, the elasticity of the brush will be reduced, so that the pressure of the brush on the commutation device will be reduced and the contact will not be tight. In this case, the rubber blocks can be bonded in situ by glue. For the elastic brush, the common problem is that the brush face is not smooth and there is a curved place. So long as the tweezers are used to straighten it and make the two brush close to each other, it can be repaired.

Note:according to the above methods for the commutator and the brush trimming, it must be carefully cleaned, especially in the slot between the several non - contact arc steel sheets on the commutator, the powder should be removed with steel, otherwise the motor will not work properly.

(3)Repair of motor open fault.

After detection, if the motor has an open fault, it can be repaired in general, because the open circuit of the motor usually is caused by the welding point removal on the centrifugal steady speed switch on the commutator and the opening of transistor in the electronic speed stabilizing device (pin off or damage). It can be repaired in accordance with the actual situation. If the solder joint is removed, it can be rewelded; if the transistor is damaged, it should be replaced.

(4)Repair of short circuit fault of motor.

The replacement method is used to repair the short circuit faults in the motor coil.

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