Overload protection circuit for a motor

Claim 1

A D.C. OVERLOAD PROTECTION CIRCUIT COMPRISING IN COMBINATION A D.C. SOURCE, POSITIVE AND NEGATIVE TERMINALS CONNECTER TO SAID SOURCE, A SWITCHABLE RECTIFIER HAVING AN ANODE, A CATHODE AND A GATE, SAID SWITCHABLE RECTIFIER BEING TURNED ON, TO PERMIT FLOW OF CURRENT FROM ANODE TO CATHODE, BY POSITIVE CURRENT FLOWING FROM ITS GATE TO ITS CATHODE WHEN A PREDETERMINED POSITIVE GATE-CATHODE VOLTAGE IS EXCEEDED, AND SAID SWITCHABLE RECTIFIER BEING TURNED OFF, TO PREVENT FLOW OF CURRENT FROM ANODE TO CATHODE, BY A NEGATIVE CURRENT FLOWING FROM ITS GATE TO ITS CATHODE WHEN A PREDETERMINED NEGATIVE GATE-CATHODE VOLTAGE IS EXCEEDED, A RESISTOR CONNECTED BETWEEN THE CATHODE OF THE SWITCHABLE RECTIFIER AND THE NEGATIVE TERMINAL, A LOAD CONNECTED BETWEEN THE ANODE OF SAID SWITCHABLE RECTIFIER AND SAID POSITIVE TERMINAL, SAID LOAD COMPRISING THE ARMATURE OF A MOTOR AND A VARIABLE RESISTOR IN SERIES, A FIRST WIPER CONNECTED TO SAID POSITIVE TERMINAL AND HAVING A FIRST POSITION IN WHICH NO CONNECTION IS MADE TO SAID ARMATURE, A SECOND POSITION IN WHICH SAID POSITIVE TERMINAL IS CONNECTED TO SAID ARMATURE THROUGH SAID VARIABLE RESISTOR, AND FURTHER POSITIONS IN WHICH PORTIONS OF SAID VARIABLE RESISTOR ARE REMOVED FROM THE CIRCUIT TO SAID ARMATURE TO INCREASE THE CURRENT FLOW THEREIN, AND A SECOND WIPER CONNECTER TO THE GATE OF THE SWITCHABLE RECTFIER AND MOVABLE IN SYNCHRONISM WITH THE FIRST WIPER BETWEEN A FIRST POSITION IN WHICH SAID SECOND WIPER IS DISCONNECTED FROM SAID D.C. SOURCE, A SECOND POSITION AND FURTHER POSITIONS, A RESISTOR THROUGH WHICH SAID SECOND WIPER IS CONNECTED TO SAID POSITIVE TERMINAL WHEN THE SECOND WIPER IS IN SAID SECOND POSITION SO THAT POSITIVE CURRENT FLOWS FROM SAID GATE TO SAID CATHODE TO TURN SAID SWITCHABLE RECTIFIER ON, AND MEANS CONNECTING SAID SECOND WIPER TO SAID NEGATIVE TERMINAL IN EACH OF SAID FURTHER POSITIONS OF THE SECOND WIPER, THE GATE VOLTAGE OF SAID SWITCHABLE RECTIFIER BEING NEGATIVE WITH RESPECT TO THE CATODE VOLTAGE OF SAID SWITCHABLE RECTIFIER WHEN THE SWITCHABLE RECTIFIER IS ON AND THE MAGNITUDE OF SAID NEGATIVE GATE-CATHODE VOLTAGE INCREASING WITH CURRENT FLOW THROUGH THE LOAD SO THAT SAID PREDETERMINED NEGATIVE GATECATHODE VOLTAGE IS EXCEEDED AND SAID SWITCHABLE RECTIFIER TURNED OFF WHEN THE CURRENT GLOWING IN THE LOAD REACHES A PREDETERMINED VALUE.