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Method and apparatus for starting single phase motors

  • US 4,843,295 A
  • Filed: 06/04/1987
  • Issued: 06/27/1989
  • Est. Priority Date: 06/04/1987
  • Status: Expired due to Fees
First Claim
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1. A system for starting an electric motor having a main winding and a start winding comprising,a solid state switch having a gate and having a first and second main terminals connectable in series with the start winding to control energization thereof,control apparatus comprisinga power supply for providing a DC bias voltage,trigger means coupled to the gate for providing a signal to the gate to turn on the switch and energize the start winding, the trigger means turning on the switch upon energization of the motor from an at rest condition,measuring means to continuously measure a wave form of one of the main winding current and start winding voltage, the measuring means integrating the entire value of each half cycle of one polarity, the measuring means including an operational amplifier, a transfer gate having an output connected to an input of the operational amplifier, a first capacitor coupled to the transfer gate, means to take a plurality of differential samples of one half cycle of the wave form and apply the samples to the first capacitor, a second capacitor connected between an input of the operational amplifier and its output and means after each differential sample to turn on the gate connecting the first capacitor to the second capacitor to transfer the charge on the first capacitor to the second capacitor while the wave form is of one polarity so that at the end of the half cycle the output of the operational amplifier equals the integration of the entire half cycle,calibration means for storing a first integrated value as a calibration value, andcomparison means for comparing the continuing integrated values to the calibration value, the trigger means interrupting the signal to the gate to turn off the switch and de-energize the start winding when the continuing integrated values reaches a threshold value which is a selected proportion of the calibration value.

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