Patent ID: 8378619
Filing Date: 2013-02-19
Classification: H02P

Abstract:
1. A motor start circuit for an induction motor with a main winding and a start winding, which are supplied with alternating current or voltage from a mains power supply, and with a start switch device serving the purpose of interrupting the current or voltage flow through the start winding after the start of the motor, the start switch device being connected to a control arrangement, said control arrangement including: a sensor system for monitoring at least two AC signals of said motor start circuit, wherein each monitored AC signal is being sensed with respect to a selected reference point; a signal adding arrangement including a signal pre-conditioning arrangement comprising a plurality of impedance devices that can adjust the magnitude and phase of the monitored AC signals to be added each to the other for a single combined AC signal; a first comparator adapted to accept the combined AC signal for comparison in instantaneous magnitude with an AC reference voltage derived from the mains supply wherein a pre-conditioning arrangement comprising a plurality of impedance devices can adjust the magnitude and phase of that mains reference relative to the combined AC signal; an integrator adapted to filter the output signal from the first comparator to a corresponding output DC signal; and a second comparator adapted to compare the output DC signal from the said integrator with a reference DC input wherein response to those predetermined differences in DC inputs provides an output signal that controls the start switch device.