Motor starting circuit

A starting circuit for an electric motor having a main winding and a start winding, said starting circuit comprising:

• means for sensing the magnitude of a current flowing in said main winding;
• means coupled to said sensing means for generating a reference level which is proportional to an average value of said main winding circuit, said generating means including reference storage means and compensation means, said reference storage means having a capacitor and a resistor in a charge path for charging said capacitor to a voltage proportional to said average value by a first factor, said compensation means providing an additional resistive charge path for charging said capacitor to a voltage proportional to said average value of main winding current by a second factor larger than said first factor, said first factor being based on a value of main winding current obtained under a locked rotor condition, and said second factor being based on a value of main winding current obtaining during normal rotational speed of a rotor of the motor;
• means for comparing said current magnitude with said reference level;
• power supply means for activating said starting circuit after initial energization of said main winding;
• and
• switching means driven by said comparing means for terminating a flow of current in said start winding when the magnitude of current in said main winding drops below said reference level, and for initiating a current flow in said start winding when the magnitude of current in said main winding rises above said reference level.