Causes & Solutions of Brushless Motor Failure

Ⅰ.What Is Brushless Motor?

The brushless DC motor is composed of a motor body and a driver and is a typical mechatronic product. Because the DC brushless motor works in a self-control mode, it will not add additional starting winding on the rotor like a synchronous motor driven by a heavy load under variable frequency speed regulation, nor will it vibrate and lose a step when the load changes suddenly. For the permanent magnets of small and medium-capacity DC brushless electric motors, the rare earth Nd-Fe-B materials with high magnetic energy levels are now mostly used. Therefore, the volume of the rare earth permanent magnet brushless motor is one size smaller than the three-phase asynchronous motor of the same capacity.

Ⅱ.Working Principle of Brushless Motor

Brushless DC motors use semiconductor switching equipment to complete electronic commutation, that is, replacing traditional touch commutators and brushes with electronic switching equipment. It has the advantages of high reliability, no reversing sparks, low mechanical noise, etc., and is widely used in advanced audio jacks, video recorders, electronic instruments, and automated office equipment.
The DC brushless motor consists of a permanent magnet rotor, a multi-pole winding stator, and an orientation sensor. The azimuth sensor changes the current of the stator winding according to the change of the rotor position. The operating voltage of the stator winding is supplied by an electronic switch circuit controlled by the output of the orientation sensor.
There are three types of orientation sensors: magnetic sensitive, photoelectric, and electromagnetic.
The brushless DC motor with a magneto-sensitive azimuth sensor is used, and its magneto-sensitive sensor material is installed on the stator assembly to detect the change of the magnetic field generated when the permanent magnet and the rotor rotate.
A brushless DC motor with a photoelectric orientation sensor is selected. The stator assembly is equipped with a photoelectric sensor material in a certain orientation. A light shield is installed on the rotor. The light source is a light-emitting diode or a small bulb. When the rotor rotates, due to the effect of the shading plate, the photosensitive element equipment on the stator will generate pulse signals intermittently at a certain frequency.
The brushless DC motor with electromagnetic orientation sensor is equipped with electromagnetic sensor components (coupling transformer, proximity switch, LC resonance circuit, etc.) on the stator assembly. When the orientation of the permanent magnet rotor changes, the electromagnetic effect will cause the electromagnetic sensor to generate a high-frequency modulation signal.

Ⅲ.Common Fault Causes & Troubleshooting Measures of Brushless Motors

1.The quiescent current of the controller should normally be within 50mA. The current at the maximum speed of the motor at no load is generally around 1.4A, and some motors are around 1.8A. When the control board is not working, the signal light on the billboard should flash in seconds/time. If the signal light does not flash when the signal is not added, check:
A. Whether the 5V voltage is normal, whether there is a short circuit in the external connector when it is abnormal, whether there is a tin short circuit on the board, etc.;
B. Whether the voltage of the second pin of the microcontroller is 5V;
C. Whether the quartz crystal works;
D. Whether the signal light is damaged.
2.Controller current & voltage adjustment
A. Current adjustment: The old program of 500W has a better running effect from 26A to 35A, and the new program has a better effect from 22A to 28A.
B. Voltage adjustment: The under-voltage sampling circuit is composed of two voltage divider resistors from the 48V or 36V power supply to the ground. Because the resistance connected to the ground is usually 1.2K, the under-voltage value and the resistance value can be calculated according to the following formula: Ra=(1.2*v- 1.2*3)/3.
Note: 1.2 is the resistance connected to the ground, and 3 is the AD value of the MCU processing under-voltage.
3.When the single-chip microcomputer on the control board can work but cannot work normally, please pay attention to the signal flashing state. The common flashing states are listed below:
A.The normal operation of the weak signal control part is about 1 second/time;
B.Slow flashing for 2 times, the circuit is in the braking state;
C.Slow flashing for 3 times, 358 inside the chip is faulty, there is a parameter error or an open circuit between the copper pin and the 31st pin of the micro-controller;
D.Slow flashing for 4 times, the upper bridge drive to the output MOS is faulty;
E.Slow flashing for 5 times, the lower bridge drive to the output MOS is faulty;
F.Slow flashing for 6 times, the phase sequence of 60 degrees 120 degrees is incorrectly connected with the motor Hall phase sequence;
G.Slow flashing for 7 times, over-current protection: the circuit between the copper pin and the 31 pins of the single-chip microcomputer and the peripheral circuit are faulty;
H.Slow flashing for 8 times, under-voltage state;
I.Fast flashing for 2 times, then switch circuit is faulty;
J.Fast flashing for 3 times, locked rotor protection;
K.The signal light flickers when the motor is rotating, the hall wire is disconnected, or the motor does not match.

Ⅳ.Brushless Motor Repair Method

Everyone knows that any machine will need to be repaired when it breaks down after a period of use. The same is true for DC brushless motors. In the process of using the DC brushless motor, there will always be some problems. So what should be known when repairing a brushless DC motor. When repairing the brushless DC motor, the repair shop has the following steps:
The first is to make a record of the original parts during the disassembly process, check the dimensions, and clean the parts. But one thing to note is that in the process of recording, be accurate, otherwise, any errors will cause the brushless DC motor to fail to install. In the repair of brushless DC motors, the oil must be cleaned. The length of the coil should be kept consistent to ensure reliable welding. Then it is dried and dipped.
After completing the above steps, you can proceed to the final assembly. During the final assembly, apply anti-rust paint on the rusty area, and then proceed with the final assembly according to the markings made previously. After the final assembly, check whether there are any parts missing or whether the motor can work normally. In the process of motor maintenance, the most important thing is to make a mark. Only when the mark is made, can the installation be accurate. It is best to draw the wiring diagram while disassembling the machine. This is the most accurate. This is the entire process of brushless DC motor repair. Only when you are familiar with these processes can you better solve the faults of the brushless motor in the brushless motor repair. From the maintenance process, it can be seen that the mark for disassembly is the most important at the beginning. Only when the mark is done can the brushless motor be installed accurately.
What should be paid attention to when repairing brushless DC motors?
1.Maintenance required unloading the equipment, do before unloading, the dust on the surface of the motor needs to be wiped clean, and the dirt on the surface also needs to be wiped clean.
2.The parts after the disassembly of the motor should be placed in a clean place, without dust.
3.The maintenance staff must be aware of all the structure of the equipment and the maintenance technology.
4.Complete dismantling tools are prepared.
5.If it is possible, carry out a major inspection test to find out where the equipment has problems and solve them in time!
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