Variable torque reduces the torque in proportion of the square of the speed. Constant Torque uses a linear relationship of torque and speed. Variable torque is used in fan and pump applications. The overload rating for variable torque is 120% for 60 seconds. Constant torque has an overload rating of 150% for 60 seconds and 200% for 3 seconds.
On loads such as a fan little torque is needed at lower speeds, as the speed increases so does the force of the air. This creates a demand for greater torque at higher speeds and lower torque at lesser speeds. Because Variable torque uses less torque at lower speeds it adds to savings on cost.
Constant torque is ideal when the torque must be the same across the entire speed range. A conveyor is a good example to use. On a conveyor, you may be moving the same amount of weight at varying speeds. You will need the percent of torque to move it at a low speed as a higher speed.
