How to determine if the motor has a malfunction

The diagnosis of motor faults mainly relies on a combination of sensory observation (seeing, listening, smelling, touching) and tool testing (measuring current, insulation resistance) to identify abnormal symptoms such as noise, overheating, vibration, etc. Here are the specific methods:

Listen to the sound:

Creaking sound: Bearing wear or internal foreign objects (stop immediately for inspection). ‌‌

Continuous buzzing sound: voltage instability, overload, or winding failure (voltage measurement or load reduction). ‌‌

High frequency whistling sound: The bearing is short of oil (add lubricating oil). ‌‌

Smell the scent:

Burnt smell: The insulation layer is burnt or short circuited (immediately cut off the power). ‌‌

Paint smell: Internal overheating (check for heat dissipation). ‌‌

Touch temperature:

Hot shell (>60 ℃): Overload, poor heat dissipation, or short circuit (stop and clean the ventilation port). ‌‌

Local overheating of bearings: lubrication failure (adding grease or replacing bearings). ‌‌

Look at the appearance:

Shell cracking/deformation: structural damage (replacement of shell). ‌‌

Damaged junction box: risk of electric shock (repair insulation layer). ‌‌

 

Tool detection method

Quantify faults using instruments:

Current measurement:

Current exceeding the set value by more than 10%: winding short circuit or bearing jamming (detected with a clamp gauge). ‌‌

Measure insulation resistance:

Resistance<0.5M Ω: The winding is damp or aged (tested with a megohmmeter and needs to be dried or replaced). ‌‌‌‌

Measure speed/vibration:

Speed decrease>10%: phase loss or excessive load (check power supply voltage). ‌‌

Vibration>0.15mm: rotor imbalance or bearing damage (correct dynamic balance). ‌‌

Key Action Principles

Immediately stop the machine: Avoid fire or electric shock when there is a burnt smell, smoke, or when the shell is electrified (tingling sensation). ‌‌

Regular maintenance: Clean the heat dissipation port monthly, measure insulation resistance annually, and replace lubricating grease preventively

 

 

To test whether the motor is damaged, a comprehensive diagnosis is required through steps such as power-off safety inspection, resistance measurement, insulation testing, and observation of power on operation. The following is the specific operation process, applicable to most household or industrial motors (such as fans, electric vehicles, washing machine motors), requiring the preparation of a multimeter (essential), an insulation shaker (optional), and a screwdriver and other tools

Safety preparation and preliminary inspection

Power off operation: Disconnect the power supply and check for residual voltage, wear insulated gloves. ‌‌

Appearance and odor inspection:

Observe whether the motor casing is burnt, deformed, or cracked.

Smell for a pungent burnt smell (indicating burnt windings). ‌‌

Manual testing:

Light rotating motor shaft: It should be smooth and free of jamming normally; If it gets stuck or makes abnormal noises, it may be due to bearing damage or rotor sweeping. ‌‌

Shaking the motor shaft: obvious looseness indicates bearing wear. ‌‌

Core electrical testing (using a multimeter)

Winding resistance measurement:

Disconnect all wiring and adjust the multimeter to the resistance range (Ω range, 200 Ω range).

Three phase motor: Measure the resistance of U-V, V-W, and W-U groups, and the difference should be ≤ 5% (if all are 2 Ω± 0.1 Ω). ‌‌

Single phase motor: Measure the main winding (with a small resistance value, such as 50 Ω) and the starting winding (with a large resistance value, such as 200 Ω), and the sum of the two should be equal to the common terminal resistance. ‌‌

Abnormal: If the resistance of a certain phase is 0 (short circuit) or ∞ (open circuit), it is damaged. ‌‌

Insulation resistance test:

Set the multimeter to the high resistance range (20M Ω), with one probe connected to the winding terminal and the other probe connected to the metal casing.

The normal value should be greater than 1M Ω (in humid environments, it can be greater than 0.5M Ω); If it is less than 0.5M Ω, it indicates insulation damage and leakage. ‌‌

Power on verification (low voltage safety test)

No load operation:

Connect to the rated voltage (such as 220V) and observe if it starts.

Normal: Smooth buzzing sound, no sparks; Abnormality: Shake, abnormal noise or smoke. Power off immediately. ‌‌

Current detection:

Measure the working current with a clamp meter and compare it with the rated value (e.g. the no-load current of a 1.5kW motor is about 2-3A).

Current exceeding 10% or three-phase imbalance>10% indicates a fault.