GB1463162A - Electric fan - Google Patents

Abstract

1463162 Control of AC motors PETER WENTIEN TSAY 25 Jan 1974 03643/74 Heading H2J A fan is driven by a split-phase motor having main and auxiliary windings M, A and a starting capacitor C, the windings being controlled by a Triac TR whose firing angle is determined by a trigger signal generator 60 in response to the setting of a manually-adjustable control resistor VR1 corresponding to a desired motor speed, a control network 30 also being provided whereby, when it is energized by closure of a switch S3, a capacitor C6 respectively charges and discharges during successive half cycles of the A.C. supply to the motor, so that the voltage across the resistor VR1 is correspondingly varied to cyclically increase and decrease the speed of the motor. During alternate half cycles the capacitor C6 is charged through diode D2 from the secondary winding of a transformer T1, also supplying a low voltage to the generator 60 through a voltage compensation means 20 which prevents variations of the voltage of the A.C. supply causing changes of motor speed. The discharge of capacitor C6 may be varied by an adjustable resistor VR2 gauged to a switch S2 which opens when VR2 has been reduced to zero, so that a high value resistor R11 is inserted in the discharge circuit to reduce to a minimum the speed variation produced by network 30. Further desired speed variations may be produced by closure of a switch S7 to connect the output of a signal generator 90 to the resistor VR1, the output being an irregular wave obtained by combining the outputs of two different low frequency relaxation oscillators R20, C7, DIAC 1 and R21, C8, DIAC 2, whereby the speed variations cause the fan to provide an air flow imitative of a natural wind. Closure of a switch S6 energizes a reversing circuit 80 comprising a Schmitt trigger Q5, Q6 and a relay coil R whereby, with the motor speed gradually reducing due to the action of network 30, the Schmitt trigger operates at a predetermined value to energize coil R whose contacts S11-S14 change over to reverse the direction of motor rotation. Features of the generator 60 are provision of (1) a resistor R8 and switch S1 which is opened to reduce the speed to zero and closed to obtain a certain minimum value; (2) circuit C4, R5 to ensure reliable starting of the motor and so prevent overcurrent during this period, and (3) a resistor R6 inserted by closure of a contact S5 of relay R to produce an increased motor speed after it has been reversed by operation of the circuit 80. The motor may be replaced by one of the commutator or shaded pole type. A basic circuit comprising members 10, 30, 50, 60, 70. Fig. 1 (not shown), may be used with various combinations of members 40, 80, 90, Figs. 2 to 5 (not shown).