The principle of the starting characteristics computation (torque, slip and current) is to consider the starting process as a sequence of successive steady states of constant slip; this is possible because the electric circuit time constants are small compared to the mechanical time constant. Based on the mathematical model of the electric circuits voltage equations and of the movement equation the absorbed current, the startup time and the heating during the startup process are studied. The paper includes the following important contributions: the expression of the electromagnetic torque produced by the field winding connected to a series resistance ra, the resistance ra optimization based on minimum startup time criterion, elaboration of a simple relation for the temperature rise during the first start and then for subsequent restarts.