Device and method for reducing the current consumption during the starting process of a single-phase a.c. asynchronous motor

Abstract

The invention relates to a device ( 1 ) for reducing the current consumption during the starting process of a single-phase a.c. asynchronous motor (M). Said device consists of a thermistor which can be mounted in series with the main winding of the motor. Advantageously, a starting capacitor ( 8 ) can be mounted in series with an auxiliary winding ( 3 ). Current and voltage peaks of the starting capacitor ( 8 ) can be advantageously reduced by a posistor ( 9 ). The thermistor ( 5 ) is mounted in series with the main winding at the beginning of the starting process, and can be bridged by a switch once the starting process is completed.

1 . An apparatus for reducing the current drawn during starting of a single-phase AC asynchronous motor, having an auxiliary winding and having a main winding, which apparatus has an NTC thermistor which can be connected in series with the main winding, characterized in that the NTC thermistor can effectively be connected in series with the main winding at the start of the switching-on process in order to limit the starting current through the main winding, and with the NTC thermistor not limiting the current through the auxiliary winding.  
   
   
       2 . The apparatus as claimed in  claim 1 , further comprising a starting circuit with a starting capacitor for producing a phase shift in the auxiliary winding arranged such that it can be connected in series with the auxiliary winding, and a PTC thermistor for limiting capacitive current surges through the starting capacitor in series with the capacitor.  
   
   
       3 . The apparatus as claimed in  claim 1 , further comprising a starting circuit with a starting capacitor for producing a phase shift in the auxiliary winding arranged such that it can be connected in series with the auxiliary winding, and an NTC thermistor for limiting capacitive current surges through the starting capacitor in series with the capacitor.  
   
   
       4 . The apparatus as claimed in  claim 1 , further comprising a switch in order to bridge the NTC thermistor after completion of the starting process.  
   
   
       5 . The apparatus as claimed in  claim 1 , further comprising a switch in order to switch off the starting circuit.  
   
   
       6 . The apparatus as claimed in  claim 1 , further comprising a control arrangement for switching the switches on and off as a function of time.  
   
   
       7 . The apparatus as claimed in  claim 6 , wherein the control arrangement is designed such that the switch can be operated before the switch.  
   
   
       8 . The apparatus as claimed in  claim 2 , further comprising an operating capacitor for producing a phase shift in the auxiliary winding with respect to the main winding in the operating state, wherein the capacitance of the starting capacitor is greater than the capacitance of the operating capacitor.  
   
   
       9 . The apparatus as claimed in  claim 2 , wherein the capacitance value of the starting capacitor is at least twice as great as the capacitance value of the operating capacitor.  
   
   
       10 . The apparatus as claimed in  claim 1 , wherein the NTC thermistor has a cold resistance of 10 to 30 Ω.  
   
   
       11 . A method for reducing the starting current on switching on a single-phase AC asynchronous motor, said method comrpsing steps of, reducing, on switching on, the current through the main winding of the motor by means of an NTC thermistor, and bridging the NTC thermistor by means of a switch after starting of the motor.  
   
   
       12 . The method as claimed in  claim 11 , comprising a further step of producing a starting phase shift in the auxiliary winding of the motor during the starting process with a starting capacitor, and reducing the current through the starting capacitor at the moment of being switched on with a resistor.  
   
   
       13 . The method as claimed in  claim 12 , wherein the resistor and the starting capacitor are disconnected from the circuit by means of a switch on reaching rated operation, before the NTC thermistor is bridged by means of the switch.  
   
   
       14 . The method as claimed in  claim 11 , wherein the current through the main winding is increased continuously during the starting process, while the current through the starting capacitor and the degree of phase shift produced by the starting capacitor are increasingly reduced.  
   
   
       15 . The apparatus as claimed in  claim 9 , wherein the capacitance value of the starting capacitor is three to five times as great as the capacitance value of the operating capacitor.  
   
   
       16 . A method as claimed in  claim 11 , wherein the bridging step is done on or after reaching rated operation.