A solid-state speed controller for capacitor motors driving ventilation fans

The authors document the design and testing of an electronic speed controller for permanent-split capacitor motors driving agricultural ventilation fans. The controller was developed and tested with three commercially available and widely used fan systems. Linearized temperature versus airflow rate characteristics were obtained. The controller circuit uses an erasable programmable read-only memory (EPROM) chip. The input to the EPROM is an analog representation of temperature converted to digital form. The digital contents then are converted to an analog signal that triggers a triac and consequently controls the voltage input in the fan motor. A linearized control characteristic can be obtained by storing appropriate voltage values in the EPROM. These values correspond linearly to the desired fan speeds