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Starting torque test

September 28, 2025
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Introduction: The importance of initial torque testing

Starting torque testing is one of the most important motor tests. It allows the assessment of a motor’s ability to overcome initial inertia and start under load. This test is especially important in industrial environments where the motor must start under full load.

Determination of the starting torque

Starting torque, or starting torque, is the torque generated when the motor starts (at zero speed). This parameter is usually expressed as a percentage of the rated torque:

  • Standard asynchronous motors: 150–200% of the rated torque

  • High torque motor: torque up to 300% of rated torque

  • Special motors (e.g. for heavy industry): Torque up to 400% of the rated torque.

Reasons for performing a starting torque test

  1. Ensures normal operation under starting conditions.

  2. Avoid overheating during startup.

  3. Ensuring compliance with mechanical load requirements

  4. Check the condition of the coil and the magnetic system.

  5. Approval of the application’s custom engine design

Standards for testing starting torque

  • IEC 60034-12     : International Standard for testing induction motors

  • IEEE 112     : Standard Test Methods for Induction Motors

  • NEMA MG-1     : American standard for electric motors and generators

  • ISO 8821     : Standard for engine performance tests

How to perform a starting torque test

1. Direct dynamometer method

Implementation phases:

  1. The motor is connected to a dynamometer.

  2. They put the system into full braking mode.

  3. You start the engine and measure the maximum torque.

  4. Data recording at different speeds

Special feature:

  • High resolution

  • It is possible to record the entire torque and speed curve.

  • Ability to repeat

Shortage:

  • Expensive equipment is required

  • a waste of time

2. Indirect method (measurement of the starting current)

Implementation phases:

  1. They measure the starting current.

  2. Calculating the torque based on the engine characteristics

  3. Compare the results with the nominal values.

Special feature:

  • Simple and fast

  • No special equipment is required.

Shortage:

  • Low resolution

  • This depends on the accuracy of the reference curve.

ABB motor files3. Accelerometer method (applies to built-in motors)

Implementation phases:

  1. The accelerometer is mounted on the motor shaft.

  2. Under real load the engine starts to work.

  3. The initial acceleration is measured and converted into torque.

Special feature:

  • On-site testing options

  • There is no need to stop the production line

Shortage:

  • Average accuracy

  • Accurate calibration required

Equipment required for testing starting torque

  1. Dynamometer     : Used to directly measure torque.

  2. Torque sensor     : Precision torque sensor

  3. Energy analyzer     : for indirect methods

  4. Control system     : for measuring acceleration

  5. Data logger     : Records test information.

  6. Cooling system     : for re-test

Factors influencing starting torque test results

  1. Supply voltage     : By reducing the voltage, the starting torque is significantly reduced.

  2. Coil temperature     : At higher temperatures the resistance is higher and the torque is reduced.

  3. Mains frequency     : has a direct influence on AC motors.

  4. Winding connection type     : delta or star

  5. Rotor design     : Rotor resistance in induction motors

  6. Environmental conditions     : altitude, humidity and temperature.

Interpretation of the starting torque test results

Expected results:

  • Corresponds to catalog values ​​(±10% tolerance).

  • Continuous   torque and speed curve 

  • Correct starting time for engine design

Signs of a problem:

  1. The torque is lower than expected     :

    • Problem with the file

    • Magnetic defects

    • Power supply problems

  2. Oscillation moment     :

    • Storage problems

    • Dizziness, balance disorders

    • Transmission problems

  3. Long start time     :

    • The motor is not designed for the load.

    • Problems with the  management system

    • excessive mechanical friction

Application of starting torque test results

  1. Drive system design     : Selecting the right inverter and control system

  2. Protection calculations     : Overload relay configuration

  3. Energy optimization     : Reduction of start-up losses

  4. Troubleshooting existing systems     : Diagnosis of mechanical and electrical problems

  5. Product quality assurance     : quality control of the final product

Safety tips for conducting starting torque tests

  1. Overheating protection     :

    • Determine the duration of the test

    • Use of a temperature control system

    • adequate ventilation

  2. Mechanical protection     :

  3. Electrical protection     :

    • Use a suitable circuit breaker.

    • Correct grounding system

    • Keep a safe distance

Testing the starting torque     for different motors

1. Three-phase asynchronous motor:

  • Star and delta connection tests

  • Please note the high starting current.

  • Control the effect of skin vertigo

2. DC motor:

  • Complete power test

  • ignition switch

  • Please note the torque characteristic curve.

3. Servo motor:

  • Dynamic reaction test

  • Measuring torque at different frequencies

  • Torque pulsation control

4. Stepper motor:

  • Checking the installation torque

  • Torque measurement at different pulse frequencies

  • Step skip management

The most advanced method for testing starting torque

  1. Dynamic frequency conversion test     :

    • Analysis of motor response to frequency changes

    •   Diagnosis of mechanical and electrical   problems

  2. Real load simulation system     :

    • Simulation of operating conditions

    • Testing under different load scenarios

  3. Combined torque and vibration test     :

    • Simultaneous analysis of torque and vibration

    • Diagnosis and balancing of bearing problems

  4. Image processing systems for analysis     :

    • Investigation of mechanical changes with high-speed cameras

    • Mechanical leak detection

Conclusion and final recommendations

Testing starting torque is one of the most important tests for electric motors and provides valuable information about the motor’s condition and efficiency. The choice of the appropriate test method depends on the motor type, the required accuracy, and the available options.

Important recommendations:

  1. Perform starting torque tests regularly.

  2. Compare the results with catalog values ​​and previous tests.

  3. Use calibration devices.

  4. Consider environmental conditions when interpreting results   .

  5. Perform comprehensive torque and speed tests on critical engines.

By performing this test regularly and properly analyzing the results, you can ensure optimal operation of your transmission system and avoid costly failures.