JPS6114754B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a starting circuit for a single-phase induction motor using a starter by connecting a positive temperature coefficient thermistor in series with the starting coil, and in particular to controlling two-phase operation time to reduce power consumption during starting. The purpose is to minimize losses.

Conventionally, the starting circuit for a single-phase induction motor (hereinafter simply referred to as a motor) using a positive temperature coefficient thermistor as a starter consists of a starting switch A such as a thermostat, a motor B, and a starting coil of the motor B connected in series, as shown in Figure 1. Connected positive characteristic thermistor C and starting capacitor D (omitted for split-phase starting motors)
I was confused. In this configuration, when the motor circuit is closed by start switch A, a positive characteristic thermistor (Fig. 4A)
point) due to self-heating due to energization, the resistance value increases to 10 ⁵
The resistance reaches ~10 ⁶ Ω (point D in Figure 4), and the starting coil B' becomes disconnected from the power supply circuit. In other words, for only a few seconds when the positive temperature coefficient thermistor has a high resistance due to self-heating, current also flows to the starting coil B' (two-phase operation), contributing to starting the motor, and after that, the main coil
Current flows only through B" and high efficiency operation begins. However, the heat-up time of the positive temperature coefficient thermistor, which determines the two-phase operation time of this motor, depends on the normal temperature resistance value of the positive coefficient thermistor, element size, Kuuri point, and resistance. It is determined by factors such as voltage, durability, motor starting current, and motor restartability. In particular, for capacitor-started motors where the starting coil current at startup is small, the heat-up time of the PTC thermistor is longer. (The amount of heat generated by a positive characteristic thermistor is proportional to the square of the current), which is considerably longer than the two-phase operation time required to start the motor, and the starting coil side circuit is opened by detecting a change in the main coil current. Compared to mechanical relays, the disadvantage is that the longer the unnecessary two-phase operation time, the greater the power consumption.

The present invention focuses on this drawback and attempts to optimize the two-phase operation time of the motor by controlling the heat-up time of the positive temperature coefficient thermistor, thereby minimizing the increase in power consumption during startup.

An embodiment of the present invention will be described below with reference to the drawings. In the figure, 1 is a power source, 2 is a starting switch such as a thermostat, 3 is a motor (single-phase induction motor), 3a is a main coil, and 3b is a starting coil. 4 is a positive characteristic thermistor; 5 is a starting capacitor that creates a phase difference between the main coil 3a and the starting coil 3b to facilitate starting; 6 is a delay timer attached to the common terminal 3c of the motor 3; 7 is the delay timer. 6 and starting coil 3 of motor 3
A resistor connected in parallel with b, which is sufficiently high compared to the impedance of the motor coil. The delay timer 6 is configured to energize the motor 3 a predetermined time after the start switch 2 is closed (see FIG. 3).

In such a configuration, after turning on the start switch 1,
A predetermined current is passed through the circuit of the resistor 7, positive temperature coefficient thermistor 4, and starting capacitor 5 by the delay timer 6 for a certain period of time _T.
Current also flows through the main coil 3a, but since the impedance of the resistor 7 is high and the current is small, there is no problem such as temperature rise in the motor coil. ), the positive temperature coefficient thermistor 4 is preheated to set the temperature of the positive coefficient thermistor to the Curie point (point C in Figure 4 = generally
120°C) (Fig. 4 A→B). After that, the main coil 3a and starting coil 3b of the motor 3 are
Since the motor 3 is energized and the motor 3 is started, the heat-up time of the positive temperature coefficient thermistor 4 can be shortened. As a result, this heat-up time can be adjusted to the two-phase operation time required for the motor, and the power consumption during startup, which was conventionally required by the startup method using the positive temperature coefficient thermistor 4, can be significantly suppressed. When the positive temperature coefficient thermistor 4 heats up and becomes a high resistance of 10 ⁵ to 10 ⁶ Ω, almost no current flows through the resistor 7.
There is no power wastage. Note that the delay time T _O by the delay timer 6 is the time required to raise the element temperature in advance so as to provide the necessary two-phase operation time when the positive characteristic thermistor 4 is connected to the motor 3.
The preheating current value determined by resistor 7 and the characteristics of the positive temperature coefficient thermistor (basic resistance value, element size,
(Kuuri point) and the required two-phase operation time of the motor.

As is clear from the above description, the present invention has a positive temperature coefficient thermistor connected in series to a starting coil, and the positive temperature coefficient thermistor is Since it is equipped with a control device that flows a predetermined current for a predetermined time without going through the motor, the two-phase operation time of the motor can be adjusted to match the time required for starting the motor by controlling the heat-up time of the positive temperature coefficient thermistor. , the high-input two-phase operation time can be kept to the necessary minimum. As a result, the activation method using a positive temperature coefficient thermistor is essentially superior to the conventional current detection type mechanical relay. This has great effects, as it eliminates the need for power during startup, and makes full use of the advantages of the positive temperature coefficient thermistor startup method, such as no contact, light weight, and standardization.

[Brief explanation of the drawing]

FIG. 1 is a starting circuit diagram of a single-phase induction motor using a positive characteristic thermistor in a conventional example, and FIG. 2 is a starting circuit diagram of a single-phase induction motor showing an embodiment of the present invention.
FIG. 3 is an explanatory diagram of the operation of the circuit of FIG. 2, and FIG. 4 is a resistance temperature curve of a positive temperature coefficient thermistor. 3...Motor, 3b...Starting coil, 4...Positive characteristic thermistor, 6...Delay timer (control device), 7...Resistor.

Claims (1)

[Claims] 1. In a device that has a positive temperature coefficient thermistor connected in series with the starting coil, before applying voltage to the motor by operating a controller such as a thermostat,
A starting circuit for a single-phase induction motor, comprising a control device that causes a predetermined current to flow through the positive characteristic thermistor for a predetermined period of time without going through the motor.