Light load control for well pump

Claim 1

In a control for the circuit for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, a low-current lockout comprising, a current transformer having its primary winding wired in series with the pump motor and having a secondary winding, an latching type relay having an input coil and having a normally closed output contact, connecting means between the output contact and the motor so that the output contact controls the flow of current to the motor, a current detector circuit having an SCR including a gate and load circuit, the load circuit being coupled to the input of the latching type relay, the current detector circuit having power input terminals connected in shunt with the motor, the current detector circuit further having a source of positive voltage supplied by the power input terminals and capable of turning the SCR on and having a source of negative voltage supplied by the secondary winding of the current transformer, means for coupling the gate of the SCR to both sources, the source of negative voltage varying in accordance with the motor current and of such magnitude as to keep the SCR turned off as long as rated current is drawn by the motor but which permits the SCR to be turned on when less than rated current is drawn by the motor with resultant actuation of the latching type relay and interruption of the motor circuit for disablement of the motor under conditions when the pump is sucking air.