Low cost, protective start from coast circuit
First Claim
1. In a single phase AC induction motor having a main winding and an auxiliary winding both connectable to an AC power source, and having a start capacitor for providing a phase shifted field for starting torque, and having start switch means for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, control circuitry for said start switch means comprising:
- main voltage detector means for sensing main winding voltage;
auxiliary voltage detector means for sensing auxiliary winding voltage;
a first voltage comparator responsive to said main and auxiliary voltage detector means and comparing auxiliary winding voltage against main winding voltage and outputting a turn-off signal when auxiliary winding voltage increases to a given cut-out value relative to main winding voltage as a function of motor speed corresponding to a given cut-out speed;
a second voltage comparator responsive to said main and auxiliary voltage detector means and comparing auxiliary winding voltage against main winding voltage and outputting a turn-on signal when auxiliary winding voltage decreases to a given cut-in value relative to main winding voltage as a function of motor speed corresponding to a given cut-in speed, said given cut-in value being a stall or overload condition voltage derived from auxiliary winding voltage during running of said motor after starting, said given cut-in speed being less than said given cut-out speed;
a third voltage comparator responsive to the output of said first voltage comparator to output a turn-off signal in response to said turn-off signal from said first voltage comparator;
a fourth voltage comparator responsive to the output of said second voltage comparator and responsive to the output of said third voltage comparator, said fourth voltage comparator being responsive to said turn-off signal from said third voltage comparator to output a turn-off signal to said start switch means to disconnect said start capacitor from said AC source, said fourth voltage comparator being responsive to said turn-on signal from said second voltage comparator to output a turn-on signal to said start switch means to connect said start capacitor to said AC source;
blanking interval means disabling said turn-on signal from said fourth voltage comparator during a blanking interval immediately after energization of said motor to prevent immediate connection of said start capacitor to said AC source and protect against an overcurrent condition if said motor is de-energized while in said running mode and then re-energized while still coasting above a given speed.
7 Assignments
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Accused Products
Abstract
Low cost, low part content motor control circuitry is provided, including blanking interval circuitry (42, 25) for preventing immediate connection of the start capacitor (5) of a single phase AC induction motor to the AC source (4) upon energization of the motor, to protect the start capacitor (5) and the start switch (6) against an overcurrent condition if the motor is de-energized while in the running mode and then re-energized while still coasting above a given speed, and to particularly prevent burn-out of the start capacitor (5) and/or start switch (6) upon reapplication of electrical power after a momentary power outage. Differently sized capacitors (42, 24) provide an early cross-over of auxiliary winding voltage relative to main winding voltage at the input of a quad comparator chip (31-34) to disable a turn-on signal for the start switch (6). Differently sized capacitors (42, 25) at the input of the chip provide the blanking interval and continue to disable the turn-on signal until auxiliary winding voltage decreases below a threshold value corresponding to a threshold speed less than or equal to cut-out speed.
64 Citations
7 Claims
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1. In a single phase AC induction motor having a main winding and an auxiliary winding both connectable to an AC power source, and having a start capacitor for providing a phase shifted field for starting torque, and having start switch means for automatically connecting and disconnecting said start capacitor to and from said AC source in starting and running modes, respectively, control circuitry for said start switch means comprising:
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main voltage detector means for sensing main winding voltage; auxiliary voltage detector means for sensing auxiliary winding voltage; a first voltage comparator responsive to said main and auxiliary voltage detector means and comparing auxiliary winding voltage against main winding voltage and outputting a turn-off signal when auxiliary winding voltage increases to a given cut-out value relative to main winding voltage as a function of motor speed corresponding to a given cut-out speed; a second voltage comparator responsive to said main and auxiliary voltage detector means and comparing auxiliary winding voltage against main winding voltage and outputting a turn-on signal when auxiliary winding voltage decreases to a given cut-in value relative to main winding voltage as a function of motor speed corresponding to a given cut-in speed, said given cut-in value being a stall or overload condition voltage derived from auxiliary winding voltage during running of said motor after starting, said given cut-in speed being less than said given cut-out speed; a third voltage comparator responsive to the output of said first voltage comparator to output a turn-off signal in response to said turn-off signal from said first voltage comparator; a fourth voltage comparator responsive to the output of said second voltage comparator and responsive to the output of said third voltage comparator, said fourth voltage comparator being responsive to said turn-off signal from said third voltage comparator to output a turn-off signal to said start switch means to disconnect said start capacitor from said AC source, said fourth voltage comparator being responsive to said turn-on signal from said second voltage comparator to output a turn-on signal to said start switch means to connect said start capacitor to said AC source; blanking interval means disabling said turn-on signal from said fourth voltage comparator during a blanking interval immediately after energization of said motor to prevent immediate connection of said start capacitor to said AC source and protect against an overcurrent condition if said motor is de-energized while in said running mode and then re-energized while still coasting above a given speed. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification