Properly Manage Heat and Time for Better Duty Cycle

Duty Cycle and Peak Current both influence the operating life of brushless servo motors.

In mechatronic designs, it is critical to manage motor heat dissipation as excess heat can affect the accuracy of a system’s mechanical components. A thorough understanding of motor thermal characteristics can ensure your brushless servomotors enhance overall system operation.

By Richard Welch Jr., Consulting Engineer - Exlar Corporation

The thermal characteristics of a brushless servo motor determine the length of time that the motor can operate in a peak range; a measurement many engineers and managers use to determine a motor’s productivity rating. This peak current range is defined as any current level between the motor’s continuous rating and its peak rating. The continuous ratings are often defined as the highest current a motor can draw while continuously dissipating the resulting motor heat in a 25°C ambient temperature.

There have long been “rules of thumb” in the brushless servo motor industry about what is acceptable to use as a duty cycle when operating in the peak or intermittent ranges. There have also been “rules of thumb” applied to how long any given motor can operate at peak current on an instantaneous basis.

Many times you will hear reference to numbers like one second or half a second as acceptable times to operate in the peak range, and it is believed that if you are in peak for one second, and then off for one second, you’ll have an acceptable duty cycle, in this case, 50%. Read more