Method and apparatus for heating electrical motors and like devices

An apparatus for heating using a coil having first and second terminals, and a power source having first and second terminals across which appears an alternating current voltage, said apparatus comprising:

• (a) first and second inputs adapted to be respectively coupled to the first and second terminals of the power source, and first and second outputs adapted to be respectively coupled to the first and second terminals of the coil;
• (b) first means providing an electrical conducting path between said first input and said first output;
• and
• (c) second means providing an electrical conducting path between said second input and said second output for substantially an entire half-cycle of said alternating current voltage at predetermined intervals each substantially equal in duration to a selected plurality of cycles of said alternating current voltage.

A control circuit for interconnection between a load circuit having first and second terminals and a source of alternating current wherein said first terminal of said load circuit is electrically connected to said source of alternating current and said control circuit is adapted for connection between said second terminal of said load circuit and said source of alternating current, said control circuit for periodically supplying a current path for unidirectional current flow through said load circuit which substantially corresponds to one-half of a cycle of the alternating current signal supplied by said source of alternating current, said control circuit comprising:

• clock means responsive to said alternating current signal for supplying a signal having a plurality of consecutive unidirectional signal pulses in substantial synchronism with successive alternate half cycles of said alternating current signal;
• counter means responsive to said signal supplied by said clock means for supplying a pulse signal each time said clock means supplies a predetermined number of said unidirectional signal pulses, said counter means supplying said pulse signal in substantial synchronism with one of said unidirectional signal pulses of said signal supplied by said clock means;
• electronic switching means having first, second and third electrodes for completing a unidirectional current path between said first and second electrodes each time a control signal is applied to said third electrode, said first and second electrodes of said electronic switching means being connected for completing a current path for coupling said unidirectional current through said load circuit when a control signal is supplied to said third electrode;
• and,
• trigger circuit means responsive to each of said pulse signals supplied by said counter means for supplying said control signal to said third electrode of said electronic switching means, said trigger circuit means including means for supplying said control signal substantially simultaneously with the initial signal transition of each of said pulse signals supplied by said counter means to complete said current path in substantial synchronism with the beginning of that alternate half cycle of said alternating current signal that causes said counter means to supply said pulse signal.

A motor heat control for an electric motor that is operated from a three-phase alternating current signal for supplying a unidirectional current to said motor corresponding to predetermined half-cycle signal intervals of a single phase of said three-phase alternating current wherein said motor is connected to said three-phase alternating current by means of three conductive paths that include contactor switches which are operable to cause said motor to cease operation and wherein a first conductive path of said three conductive paths remains established when said contactor switches are operated to cause said motor to cease operation, said motor heat control being connected in shunt circuit arrangement with the contactor switch included in the second conductive path of said three conductive paths to selectively and periodically establish a current path through said first and second conductive paths and at least one winding of said motor, said motor heat control comprising:

• clock means connected between said first and second conductive paths for receiving a single phase signal of said three-phase alternating current signal, said clock means including means for supplying a signal pulse in substantial synchronism with alternate half-cycles of said single phase signals;
• counter means for counting the number of signal pulses supplied by said clock means, said counter means including means for supplying a count pulse each time said clock means supplies a predetermined number of said signal pulses, said count pulse being supplied by said counter means in substantial synchronism with the beginning of that alternate half cycle of said single phase signal that results in the signal pulse supplied by said clock means which causes said counter means to supply said count pulse;
• controlled semiconductor means having an anode electrode, a cathode electrode and a gate electrode for completing said current path through said first and second conductive paths and said motor windings, said anode and cathode electrodes being connected to provide a shunt circuit path around said contactor switch of said second conductive path, said controlled semiconductor means establishing a unidirectional current path between said anode and cathode electrodes in response to a control signal supplied to said gate electrode;
• and,
• trigger circuit means responsive to each count pulse supplied by said counter means for supplying said control signal to said gate electrode of said controlled semiconductor means in substantial synchronism with each of said count pulses.

Improved apparatus for heating an electrical motor when said motor is shut-down, said apparatus being of the type including an electronic switch that is connected between one terminal of a source of alternating current and one terminal of said motor that is electrically connected to a winding of said motor, said electronic switch having a control electrode and being responsive to a control signal that is supplied to said control electrode during a time interval in which the electrical signal supplied by said source of alternating current is of a predetermined polarity to induce unidirectional curent flow through said electronic switch and at least one winding of said motor for the remaining portion of the half-cycle in which said electrical signal supplied by said source of alternating current is of said predetermined polarity, wherein the improvement comprises:

• means for producing a plurality of output signals, each of said plurality of output signals being separated in time from a preceding one of said plurality of output signals by a predetermined interval greater than one cycle of the source of alternating current;
• and
• means responsive to said plurality of output signals and to said electrical signal supplied by said source of alternating current for providing said control signal to said control electrode of said electronic switch substantially at the beginning of a single half-cycle which follows the production of each of said plurality of output signals and in which said electrical signal supplied by said source of alternating current is of said predetermined polarity, said predetermined time interval being selected to effect a desired amount of heating in said motor.