Motor control circuit

In a control circuit adapted for use with a motor having a set of main windings and a set of start-up windings, the combination comprising

• an oil pressure responsive circuit responsive to the lubricant pressure in the motor,
• a thermal protection circuit responsive to the temperature of the motor,
• a first transistor controlled by both the oil pressure responsive circuit and the thermal protection circuit,
• a second transistor,
• first switching means controlled by said first and second transistors to selectively energize the start-up windings of the motor,
• a limit switch responsive to a limit condition on the motor operation,
• a lock-out circuit responsive to the actuation of the limit switch to inhibit conduction of the second transistor to prevent operation of the motor,
• reset means to reset the lock-out circuit,
• a time delay circuit actuated by the energization of the start-up motor windings by the first switching means, and
• second switching means operated by the time delay circuit to energize the main motor windings after a predetermined time delay.

In a control circuit for a compressor motor in a refrigeration system, the motor having start-up and running-speed windings, the combination comprising

• a pair of contactors, a respective one connected to energize each of the start-up and running-speed windings,
• a lubricating oil pressure responsive circuit,
• a thermally responsive circuit,
• first switching means responsive to the lubricating oil pressure responsive circuit and the thermally responsive circuit to actuate the contactor for the start-up windings,
• a time delay circuit responsive to the actuation of the contactor for the start-up windings,
• second switching means connected to and controlled by the time delay circuit and connected to actuate the contactor for the running-speed windings after a time delay from actuation of the start-up windings,
• a thermostatic switch through which power is supplied to both the first and second switching means to regulate motor operation to achieve the desired temperature condition,
• a limit switch connected in series with the motor contactors and responsive to a high refrigerant pressure to prevent motor operation, and
• a lock-out circuit connected to the first switching means and receiving power through the thermostatic switch and responsive to the operation of the limit switch to prevent motor operation until reset by the thermostatic switch.

In a control circuit adapted for use with a motor usable as a compressor in a refrigeration system, the motor having a set of main running-speed windings and a set of start-up winding, the combination comprising

• a first contactor through which power is transmitted to the start-up windings of the motor,
• a second contactor through which power is transmitted to the main windings of the motor,
• first and second triacs each connected to control a one of the first and second contactors,
• first and second relays each connected to control a one of the first and second triacs and each having a coil,
• first and second transistors connected in a series circuit with the coil of the first relay such that if both of the first and second transistors are conductive, the relay coil will be energized,
• a third transistor connected in series with the coil of the second relay to control the operation thereof,
• an OR-circuit junction controlling the state of conductivity of the first transistor to turn it off when a voltage signal is created thereat,
• a plurality of thermally sensitive resistances imbedded in the motor,
• a respective operational amplifier connected to each of the thermally sensitive resistances and responsive to the resistances thereof to create a voltage signal at the OR-circuit junction when a high temperature condition exists,
• a lubricating oil pressure responsive switch,
• an oil pressure protection timing circuit,
• an operational amplifier receiving input from the oil pressure responsive switch and the oil pressure timing circuit to create a voltage at the OR-circuit junction if the oil pressure responsive switch doesn't close within a fixed timing period following motor start-up,
• a first programmable unijunction transistor controlling the operation of the third transistor,
• an RC timing element connected to the first unijunction transistor to trigger it after a time delay,
• a fourth transistor controlling current flow to the time delay means,
• a first optical isolator responsive to the energization of the first contactor to actuate the fourth transistor to actuate the RC timing element,
• a second programmable unijunction transistor controlling the operation of the second transistor,
• a thermostatic switch connected to supply power to the first and second relay coils, the second, third and fourth transistors and the first and second unijunction transistors,
• a limit switch connected in series with the first and second triacs to prevent motor operation upon the exceeding of a predetermined limit condition,
• a second optical isolator connected to the second unijunction transistor to trigger the second unijunction transistor into conduction to lock out operation of the second transistor and thereby the motor upon the opening of the limit switch,
• biasing means to rest the second unijunction transistor after power is removed and restored by operation of the thermostatic switch, and
• a light emitting diode connected to the second unjunction transistor to provide a visual display when the transistor is in its triggered state.