Three-phase AC servo motors are widely used, but after long-term operation, various failures will occur. It is an important work to prevent the expansion of the fault and ensure the normal operation of the equipment to determine the cause of the fault in time and deal with it accordingly.

Motor encoder alarm

1. Cause of failure

① Wiring error;

②Electromagnetic interference;

③Encoder hardware damage caused by mechanical vibration;

④ Pollution caused by the on-site environment;

2. Troubleshooting

①Check the wiring and eliminate errors;

② Check whether the shielding is in place, check whether the wiring is reasonable and solve it, and add a filter to improve it if necessary;

③ Check the mechanical structure and make improvements;

④ Check whether the inside of the encoder is polluted and corroded (dust, oil, etc.), and strengthen the protection;

3. Installation and wiring standards

①Try to use the original cable;

② Separate the cables to keep them as far away from the polluted wiring as possible, especially the highly polluted wiring;

③ Always use the internal power supply whenever possible. If a switching power supply is used, a filter should be used to ensure that the power supply reaches the cleanliness level;

④ Always ground the common terminal;

⑤ Keep the encoder housing insulated from the machine structure and connect to the cable shield;

⑥ If the encoder cannot be insulated, the cable shield can be connected to the ground (or dedicated terminal) on the encoder housing and the drive frame.


Motor shaft broken

1. Cause of failure

①The unreasonable mechanical design leads to excessive radial load force;

②The load end is stuck or severely overloaded;

③The motor and the reducer are not concentric when assembling.

2. Troubleshooting

①Check the maximum radial load force that the motor sample can bear, and improve the mechanical design;

②Check the operation of the load end, confirm the actual process requirements and make improvements;

③ Check whether the load is running stably and whether there is vibration, and improve the accuracy of mechanical assembly.


The no-load current of the motor is unbalanced, and the three-phase difference is large

1. Cause of failure

①The head and tail of the winding are connected wrongly;

②The power supply voltage is unbalanced;

③ There are faults such as inter-turn short circuit and coil reverse connection in the winding.

2. Troubleshooting

①Check and correct;

②Measure the power supply voltage and try to eliminate the imbalance;

③ Eliminate winding faults.


Abnormal noise when the motor is running

1. Cause of failure

①The bearing is worn or there are foreign objects such as sand particles in the oil;

②The rotor core is loose;

③The bearing is short of oil;

④ The power supply voltage is too high or unbalanced.

2. Troubleshooting

①Replace the bearing or clean the bearing;

②Repair the rotor core;

③ Come on;

④Check and adjust the power supply voltage


The motor is difficult to start. When the rated load is used, the motor speed is much lower than the rated speed.

1. Cause of failure

①The power supply voltage is too low;

②The face-connected motor is misconnected;

③The rotor is welded or broken;

④The rotor local coil is wrongly connected or reversely connected;

③ Too many turns are added when repairing the motor winding;

⑤ Motor overload.

2. Troubleshooting

①Measure the power supply voltage and try to improve it;

② Correct the connection method;

③ Check the welding and breakpoints and repair them;

④Find out the wrong connection and correct it;

⑤Restore the correct number of turns;

⑥ load shedding.


After the power is turned on, the motor cannot rotate, but there is no abnormal noise, no smell or smoke?

1. Cause of failure

①The power supply is not connected (at least two phases are not connected);

②The fuse is blown (at least two phases are blown);

③ The overcurrent relay is adjusted too small;

④The wiring of the control equipment is wrong.

2. Troubleshooting

① Check the power circuit switch, fuse, and junction box for breakpoints, and repair them;

②Check the fuse type and the cause of the fuse, and replace the fuse with a new one;

③ Adjust the setting value of the relay to cooperate with the motor;

④ Correct the wiring.


The motor vibrates greatly during operation

1. Cause of failure

①The bearing clearance is too large due to wear;

②The air gap is uneven;

③The rotor is unbalanced;

④The shaft is bent;

⑤ The coaxiality of the coupling (pulley) is too low.

2. Troubleshooting

①Repair the bearing and replace it if necessary;

② Adjust the air gap to make it uniform;

③ Correct the rotor dynamic balance;

④ Align the shaft;

⑤Re-calibrate to make it meet the requirements.


The motor does not rotate and there is a buzzing sound after power on

1. Cause of failure

①The rotor winding has an open circuit (one-phase disconnection) or one-phase power loss of the power supply;

②The beginning and end of the winding lead wire are wrongly connected or the winding is internally reversed;

③ The contact of the power circuit is loose, and the contact resistance is large;

④The motor load is too large or the rotor is stuck;

⑤ The power supply voltage is too low;

⑥The assembly of the small motor is too tight or the grease in the bearing is too hard;

⑦The bearing is stuck.

2. Troubleshooting

①Find out the breakpoint and fix it;

②Check the winding polarity; judge whether the winding end is correct;

③Tighten the loose wiring screws, use a multimeter to determine whether each connector is falsely connected, and repair it;

④Reduce load or detect and eliminate mechanical failure;

⑤ Check whether the specified surface connection method is wrongly connected; whether the voltage drop is too large due to the thin power wire, and correct it;

⑥ Reassemble to make it flexible; replace qualified grease;

⑦Repair the bearing.


Bearing overheating?

1. Cause of failure

① Too much or too little grease;

②The oil quality is not good and contains impurities;

③ Improper fit between the bearing and the journal or end cover (too loose or too tight);

④The inner hole of the bearing is eccentric and rubs against the shaft;

⑤ The motor end cover or bearing cover is not leveled;

⑥ The coupling between the motor and the load is not calibrated, or the belt is too tight;

⑦The bearing clearance is too large or too small;

⑧ The motor shaft is bent.

2. Troubleshooting

①Add grease as required (1/3-2/3 of the volume);

②Replace the clean lubricating grease;

③If it is too loose, it can be repaired with adhesive, and if it is too tight, it can be used to grind the inner hole of the journal or end cover to make it suitable;

④ Repair the bearing cover to eliminate the rubbing point;

⑤ Reassembly;

⑥Re-calibrate and adjust the belt tension;

⑦Replace new bearings;

⑧ Correct the motor shaft or replace the rotor.


Motor overheating or even smoking?

1. Cause of failure

①The power supply voltage is too high;

② The power supply voltage is too low, the motor is running with rated load, and the current is too high to cause the winding to heat up;

③ When repairing and dismantling the winding, the hot dismantling method is used improperly, which will burn the iron core;

④The motor is overloaded or starts frequently;

⑤The motor is out of phase and runs in two phases;

⑥After rewinding, it is determined that the dipping paint of the winding is not sufficient;

⑦Ambient temperature is high, there is a lot of dirt on the surface of the motor, or the ventilation duct is blocked.

2. Troubleshooting

① Reduce the power supply voltage (such as adjusting the tap of the power supply transformer);

②Increase the power supply voltage or change the thicker power supply wire;

③ Overhaul the iron core and remove the fault;

④Reduce the load; control the starting according to the specified number of times;

⑤Resume three-phase operation;

⑥ Adopt secondary dipping and vacuum dipping process;

⑦Clean the motor, improve the ambient temperature, and take cooling measures.

Editor: Huang Fei

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