A constant torque load maintains consistent resistance regardless of motor speed, typical of conveyor systems, positive displacement pumps, and compressors requiring constant force throughout their operating range. Unlike variable torque loads, constant torque applications demand full motor horsepower at all speeds, limiting energy savings from speed reduction.
Technical Characteristics
Constant torque loads include screw compressors and gear-driven equipment. Motor current and horsepower requirements remain nearly constant even at reduced speeds. HVAC applications are uncommon but include certain oil injection compressor systems and fixed-displacement hydraulic pumps operating at variable speeds.
Motor Selection Requirements
Constant torque loads typically require oversized motors rated at 1.5 times design speed to prevent overheating during low-speed operation. These motors require variable frequency drive (VFD) specifications that include vector control or sensorless vector methods to maintain torque under varying conditions.
HVAC Relevance
Few HVAC systems operate with constant torque loads. Understanding this classification helps engineers avoid applying VFDs to applications where energy savings are minimal. When constant torque loads operate in HVAC systems, soft starters may provide better cost-effectiveness than VFDs.