Selenium rectifiers for high-temperature operation

THE development of the selenium rectifier has provided design engineers with a reliable, maintenance-free source of d-c power. However, certain inherent thermal characteristics of the device impose many limitations on its application. Normally, the operation of the rectifier in ambient temperatures above 45 degrees centigrade (C) requires that the power output be derated to protect the unit or that additional equipment be provided for forced cooling. Operation at temperatures above 90 C severely reduces the life expectancies of the selenium cells in spite of the precautionary measures just mentioned.