Which equation is used to calculate the rpm of a belt-driven fan?

The equation used to calculate the RPM (revolutions per minute) of a belt-driven fan is based on the relationship between the diameters of the pulleys and the speed of the motor.

The correct formula states that the motor pulley diameter multiplied by the motor RPM, divided by the fan pulley diameter, gives you the fan's RPM. This relationship arises because the RPM of the fan is inversely proportional to the diameter of the pulleys. As the diameter of the fan pulley increases, the fan speed decreases, and vice versa.

This equation effectively takes into account how the different sizes of the pulleys will drive the fan at a different speed than the motor itself. When the motor turns its pulley, it drives the belt which, in turn, affects how fast the fan pulley turns based on their sizes.

Understanding this relationship is essential for properly sizing and selecting fan systems in applications to ensure they operate effectively within their designed parameters.