A SOLID-STATE SPEED CONTROLLER FOR CAPACITOR MOTORS DRIVING VENTILATION FANS

This paper documents the design and testing of an electronic speed con troller for permanent-split capacitor motors driving agricultural vent ilation fans. The controller was developed and tested with three comme rcially available and widely used fan systems. Linearized temperature versus airflow rate characteristics were obtained. The controller circ uit uses an erasable programmable read-only memory (EPROM) chip. The i nput 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 in put to the fan motor. A linearized control characteristic can be obtai ned by storing appropriate voltage values in the EPROM. These values c orrespond linearly to the desired fan speeds.