Pt Components, Inc.

Fmc Corporation

Dennis K Lorenz

Steven F Chmiel

Victor A Murn

Richard A Wrege

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.

Low cost, protective start from coast circuit

In a single phase AC induction motor having a main winding (1) and an auxiliary winding (2) both connectable to an AC power source (4), and having a start switch (6, 74) for automatically connecting and disconnecting the auxiliary winding (2) to and from the AC source (4) in starting and running modes, respectively, and having a user operated reversing switch (207-212) for reversing the voltage polarity applied from the AC source (4) to one of the windings relative to the other winding, low cost circuitry is provided for detecting the polarity reversal by sensing when one of the main and auxiliary winding voltages shifts from a leading to a lagging position relative to the other winding voltage, whereupon the circuit automatically instantly reconnects the auxiliary winding (2) to the AC source (4) to immediately apply reverse torque. A first voltage comparator (221) senses a given polarity and magnitude of main winding voltage, and a second voltage comparator (222) senses a given polarity and magnitude of auxiliary winding voltage. The output of the second comparator (222) is differentiated (282), and a third voltage comparator (223) compares output pulses (270) from the first comparator (221) and differentiated output pulses (288) from the second comparator (222) and instantaneously senses polarity reversal when one of the pulses shifts relative to the other, and in turn actuates the start switch (6, 74).

Low cost instant reversing circuit

The motor braking system for use with an alternating current motor and an AC power source includes a power circuit for supplying a DC braking current to the motor. A capacitor which was charged during motor operation, discharges when the motor is turned off and thus provides a pulse of energizing current to a contactor which quickly connects the power circuit to the motor and starts the electric braking cycle as soon as the AC source is disconnected from the motor. A timing circuit is also started and maintains the energizing current for a predetermined amount of time while the motor is coming to a stop. A mechanical brake may also be used to complete the stopping sequence if desired, with the mechanical brake being engaged when the braking current is terminated.

Growing community of inventors

Brookfield, WI, United States of America

Dennis K Lorenz