JPS5947556B2 - motor starting circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a starting circuit for a capacitor phase advance type single-phase AC motor having a phase advance winding.

As is well known, as a means for temporarily increasing the torque at the time of starting a capacitor phase advance type single-phase AC motor, there is a method of connecting a starting capacitor in parallel with the phase advance capacitor for a certain period of time.

In this case, the same main power source as the input of the motor is generally used as the drive power source for the clock switching circuit for cutting off the starting capacitor after a certain period of time. FIG. 1 shows an example of a conventional starting circuit for this type of motor. In the figure, 1 is a single-phase AC motor equipped with a main winding 2 and a phase advancing winding 3, Cl is a phase advancing capacitor, and C2 is a starting capacitor. Phase advance capacitor C
l is always connected to the phase advancing winding 3, and the starting capacitor C2 is connected through the NC contact of the starting switching relay 5 when the AC supply power is not turned on and when the power switch SW
For a certain period of time (usually several seconds to several tens of seconds) after I is turned on, it is connected in parallel with the phase advance capacitor C2. Reference numeral 4 denotes a timing circuit for driving the start-up switching relay 5, which excites the start-up switching relay 5 after the above-mentioned predetermined time period when the voltage of the AC power supply is applied through the main power input line 6 and T.

The contact is switched to the No side by the excitation of the start switching relay 5, and the start capacitor C2, which had been connected in parallel to the phase advance capacitor Cl and had the role of increasing the starting torque of the motor 1, is connected to the resistance via the No contact. R1, and its residual charge is discharged through resistor R1. Thereafter, when the power switch SWI is turned off, the excitation of the start switching relay 5 through the timing circuit 4 disappears, and the start capacitor C2
is again connected in parallel with the phase advancing capacitor through the NC contact in preparation for the next start-up. By the way, in such a conventional startup circuit, when a momentary interruption of the main power supply (AC supply power) occurs due to a power outage accident, the startup switching circuit immediately changes to the state at startup, that is, the startup capacitor is in parallel with the phase-advancing capacitor. It will return to the state where it is connected to. on the other hand,
If the power source is cut off or short-circuited while the AC motor is rotating, a braking action will occur due to the self-starting force. This effect becomes particularly noticeable when the motor input line is short-circuited because the starting capacitor is connected in parallel to the phase advance capacitor, and the rotational speed immediately decreases. Normally, a large number of other loads are connected to the power supply line of the motor, and a power outage in this state is considered to be equivalent to a short circuit of the motor input line.
Power outages of 0 to several 100 milliseconds occur relatively frequently. As a means to prevent a significant drop in rotation of the motor due to such instantaneous interruptions, an auxiliary power supply with a long voltage holding time may be separately prepared for the start-up switching circuit, but the cost for this is not prohibitive.

Another option is to set the startup capacitor to shut off when power is not applied to the startup circuit, and connect it to the phase advance capacitor only for a certain period of time after the power is turned on. Although the problem is solved, when the power is turned on for normal startup, a large inrush current is generated when connecting the startup capacitor, which may damage the startup capacitor switching circuit. The present invention was developed in view of the above circumstances, and is used as an input power source for a starting circuit that switches on and off the starting capacitor. With a simple configuration that utilizes the voltage generated at the coupling terminal of the phase advance coil, the rotational connection time of the motor is extended when the input power supply to the motor is momentarily cut off. FIG. 2 shows an embodiment of the present invention.

In the figure, the basic configuration of each part is the same as in FIG.
The difference is that in addition to the power supply, the voltage at the joint terminal of the phase advance capacitor C1 and the phase advance coil 3 (phase advance voltage) is received through the line 8. Note that 9 is a rectifying diode. That is, if the main power input lines 6 and 7 are disconnected or short-circuited while the motor 1 is rotating, an electromotive force is generated between the main power input line 6 and the phase-advanced power line 8 due to the self-generation of the motor 1. Therefore, the operation of the timing circuit 4 and the start switching relay 5 is maintained for a predetermined time, and the contact remains connected to the NO side, so that the start capacitor C2 can immediately return to the state where it is connected in parallel with the phase advance capacitor C1. Prevented. Of course, if the above-mentioned disconnection or short-circuit is not restored within a predetermined time, or if the power switch SWl is turned off, the electromotive force due to self-generation of the motor disappears, and the start switching relay 5 is also energized. Due to this, the contact switches to the NC side, and the starting capacitor C2 is connected in parallel with the phase advance capacitor C1 in preparation for the next starting. In the embodiment shown in FIG. 2, the connection is made using the voltage between the main power input line 6 and the phase-advanced power line 8, but the main power input lines 6 and 7 are exchanged with each other to Power input line 7 and phase advance power line 8
Alternatively, the voltage between the two may be used. As described above, according to the present invention, with a simple configuration, it is possible to prevent a decrease in rotational speed of a capacitor phase advance type single-phase motor at the time of momentary interruption of the input power supply.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional example of a motor starting circuit, and FIG. 2 is a diagram showing an embodiment of the motor starting circuit according to the present invention. 1...Electric motor, 2...Main winding, 3...
... Phase advance winding, 4... Timing circuit, 5...
...Start switching relay, C1... Phase advance capacitor, C
2...Start capacitor.

Claims (1)

[Claims] 1. In a capacitor phase advance type single-phase AC motor having a main winding and a phase advance winding, and a phase advance capacitor connected to the phase advance winding, the motor is connected in parallel to the phase advance capacitor via a switching contact. and a starting capacitor that is connected to the motor, and after a predetermined period of time has elapsed since input power of the motor is turned on, the starting capacitor is disconnected from the phase advance capacitor, and the connection with the phase advance capacitor is restored by cutting off the input power supply. and a start switching circuit for driving the switching contact,
and a connection point between the motor phase advance winding and the phase advance capacitor is connected to the start switching circuit, and when the input power source is cut off, the switching contact is maintained in the same state by a voltage generated at the connection point, A motor starting circuit characterized in that the starting capacitor is extended from being connected to a phase advancing capacitor.