As many different load steps as needed can be programmed for a given motor-under-test, or a continuous speed vs. torque curve can be generated.

To measure a specific Load Point, the dynamometer is set to control in either speed mode or torque mode, depending on customer preference. If the dynamometer is controlling speed (speed mode testing), then a speed is established by the dynamometer and torque is produced based on the capabilities of the motor. If the dynamometer is controlling torque (torque mode testing), then a load is established by the dynamometer and speed is produced based on the capabilities of the motor. In either case, once the desired point is established, the tester can measure speed, torque, voltage and current (amps) depending on how the individual tester is configured.

Another common load point is known as “Locked Rotor” or “Stalled Torque”. A full current is applied to a Hysteresis Brake, Dynamometer, or by simply clamping or “locking” the motor shaft and energizing the motor. More torque is produced by the Dynamometer/Brake than the motor can produce. In this state the shaft cannot turn, simulating the rotor being “locked” or “blocked”.

This test is very hard on a motor. There is a large amount of current that flows into the rotor, causing it to heat up rapidly. As a result, this test must be performed very quickly. A motor, with a locked rotor, draws up to six or seven times its rated current (sometimes more). The power supply used must be capable of regulating the motor voltage adequately during rapid changes in current to ensure the proper voltage is maintained when the data is being taken. ESW can suggest several levels of power supply performance to meet testing requirements in your budget.

Locked rotor torque testing is important. If the motor cannot produce enough torque to overcome the friction in the load, as it sits without rotating, the motor can be energized but it will not start the load. If the motor remains in this state for very long it will overheat and fail.