JPS6331476Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a thermal protector, and relates to a thermal protector having a simple structure and a self-holding function.

FIG. 1 shows the configuration of a conventional automatic return type thermal protector. In the figure, 1 and 2 are input terminals, 3 is a heater, 4 and 5 are contacts, and 6 is a bimetal that spans between the contacts. Now, input terminals 1 and 2
When inserted into a part of the load circuit to be protected, a load circuit is formed that returns from the power supply to the power supply through the heater 3, contact 4, bimetal 6, and contact 5.
A load current flows here, and the heat generated by the heater expands and deforms the bimetal as shown by the dotted line, so that contacts 4 and 5 open. Therefore, when the load current becomes an overcurrent, the load circuit is cut off. When the load circuit is cut off, the heater 3 stops generating heat, so the bimetal 6 cools down over time, and the contacts 4 and 5 automatically return to normal. When such a conventional automatic reset type thermal protector is installed in a device used for unmanned operation, contacts 4 and 5 will repeatedly open and close in the event of a permanent failure of the device, which will not only cause the contacts to burn out but also require protection. The equipment is also often accompanied by abnormal heat generation.
Therefore, for devices used for unmanned operation, for example, contacts that have been opened due to overcurrent may be mechanically held, and then during periodic inspections, an inspector can manually return the contacts using a push button. A manual reset type thermal protector configured as follows was often used. However, such conventional manual return type thermal protectors require a manual return operation by an inspector, which limits the environment in which a device equipped with the protector can be installed. For example, when equipped with a submersible pump that is used submerged in an aquarium, manual return operation is difficult.
In order to facilitate this, a remote control mechanism from outside the aquarium is required, which has the disadvantage of complicating the configuration.

To overcome this drawback, a thermistor with positive characteristics (the correlation coefficient between temperature and resistance value is positive) is inserted into the load circuit, and the bimetal is continuously heated in response to the heat generated by the thermistor. in,
A configuration that realized a self-holding function and made it possible to manually restore the load circuit by shutting off the power was introduced in 1972.
It is disclosed in Publication No. 28113 (Utility Model Application Publication No. 49-86339).

That is, as shown in FIG. 1A, a load circuit including a thermistor 4 with a positive characteristic and a load 7 connected in series with the thermistor 4 is formed for the power supply 6 via a switch 5, and A load side path is formed between the thermistor 4 and the load 7, branching in parallel to the load 7 and extending to the power return line, and in the side path, a bimetal contact ( (make contact) 8 is provided.

After the switch 5 is turned on, the load current flowing into the load circuit passes through the thermistor 4, and in response, the thermistor 4 generates heat and heats the bimetal contact 8, but the load current reaches a predetermined value. When the increase is greater than that, the sufficiently heated bimetallic contact 8 closes and forms a bypass for the load 7.
This cuts off the load current flowing to the load 7,
At the same time, by increasing the current flowing through the thermistor 4 (by the amount by which the load 7 is bypassed), the bimetal contact 8 is ensured to close due to further heating, and from then on, the manual opening of the switch 5 is performed. As a result, the bimetallic contact 8 is self-maintained in the closed state until the heat generation of the thermistor 4 is stopped and the bimetallic contact 8 is appropriately cooled.

However, in the configuration disclosed in Japanese Utility Model Publication No. 52-28113, the load 7 is bypassed via the bimetal contact 8 when the bimetal contact 8 is closed. In addition, when the power is cut off, that is, when a device that operates as a generator during deceleration is connected as a load, the back electromotive force derived from the power generation action during deceleration in the device may cause a short circuit via the bimetal contact 8. As a result, the contact 8 will be damaged in a short period of time due to the excessive bypass current passing through the contact 8, making it almost impossible to put it into practical use.

Therefore, in the actual circuit configuration, as shown in FIG. 1B, it is necessary to insert a current limiting resistor 9 into the bypass, and in this case, the resistance value of the resistor 9 is From the viewpoint of limiting the bypass current derived from the back electromotive force in the load 7 to an appropriate value, it should be determined depending on the electromotive force, but the determination is based on the self-current generated when the bimetal contact 8 is closed. This also limits the self-holding current that passes through the thermistor 4 via the holding circuit, so if a high resistance value is required for the resistor 9 in terms of back electromotive force, this will lead to a lack of self-holding current, and both It is often not possible to find a compromise in the value of This situation is made even more serious by the fact that the resistance value of the resistor 9 has a large contribution rate to the self-holding current of the thermistor 4 due to the circumstances in which it is applicable. The disadvantage was that not only the load was considerably restricted, but also the design work was difficult to carry out.

In view of the limitations of applicable loads and the difficulty of design work in the conventional technology mentioned above, this idea was developed using a break provided in a thermally deformable body that responds to heat from a heater that generates heat depending on the load current. By attaching a make contact that closes when the load current is interrupted by opening the contact and passes the self-holding current to the self-holding circuit including the heater, when forming the self-holding circuit, the electrical connection between the self-holding circuit and the load is reduced. The present invention aims to provide an excellent thermal protector that solves the above-mentioned problems by cutting off the physical connection, removes restrictions on applicable loads, and facilitates design work.

FIG. 2 shows the structure of a thermal protector which is an embodiment of this invention. In the figure, numerals 1 to 6 indicate the same components as 1 to 6 in FIG. Reference numeral 7 is an input terminal of the self-holding circuit, and is connected to a power source (not shown). 8 and 9 are make contacts of the bimetal 6; the contact 8 is connected to the input terminal 7, and the contact 9 is connected to one end of the heater 3.

Now, when the load current flowing through the heater 3 in the load circuit becomes an overcurrent, the bimetal 6 expands and deforms as shown by the dotted line, and the contacts 8 and 9 are electrically connected. Therefore, a self-holding circuit is formed that goes from the input terminal 7 connected to the power supply through the contacts 8 and 9 to one end of the heater 3 and returns to the power supply via the heater, so that the self-holding circuit flows in place of the load current. The expansion deformation of the bimetal 6 is maintained by the heat generated by the self-holding current passing through the circuit. In this way, the load circuit is maintained in the cut-off state until the power supply to the input terminal 7 is cut off.

FIG. 3 shows an example of the use of a thermal protector which is an embodiment of this invention. In the same figure, 10
is a thermal protector which is an embodiment of this invention, 11 is a power source, one end is connected to the input terminal 1, the other end is connected to one end of the power switch 12, and further,
The other end of the switch is connected to input terminal 7 and also to input terminal 2 through main winding 13 of the motor. If you close the power switch 12 now,
Under normal operating conditions, power supply 11, power switch 1
2. A load current flows through the main winding 13, the contacts 5 and 4, and the heater 3 to the load circuit leading to the power source 11, thereby driving a motor (not shown). On the other hand, when the load current becomes an overcurrent, the bimetal 6 expands and deforms to electrically connect the contacts 8 and 9 and maintain that state, thereby cutting off the load current and stopping the motor. When an inspector or the like detects this state and opens the power switch 12, the current passing through the heater 3 is cut off, so that the bimetal 6 is restored and the contacts 5 and 4 are electrically connected. , a load circuit within the thermal protector 10 is formed. Next, when an inspector or the like inspects and repairs the motor and removes the cause of the overcurrent and closes the power switch 12 again, the motor is driven because the load current flows to the main winding 13 through the load circuit. .

In the embodiment shown in FIG. 2, instead of the bimetal 6, various heat-sensitive deformable bodies that deform by heat can be used.

As described above, according to this invention, the break contacts 4 and 5 provided on the thermally deformable body 6 respond to the heat from the heater 3, which generates heat depending on the load current, are opened and closed in conjunction with the interruption of the load current. However, by configuring the self-holding circuit including the heater 3 to include make contacts 8 and 9 for passing the self-holding current, the overcurrent flowing in the load circuit passes through the heater 3 and heat generation there increases. In response to this, the thermally deformable body 6 deforms and the gray contacts 4 and 5 open, and when the load is cut off, the make contacts 8 and 9 are closed in conjunction with this, and the load circuit is electrically disconnected. By forming a completely independent self-holding circuit in the self-holding circuit, it is possible to prevent the back electromotive force from being transmitted to the self-holding circuit when the load is cut off, thereby completely eliminating restrictions from the perspective of the back electromotive force regarding applicable loads. Not only can this be removed, there is no need to insert a current limiting resistor derived from the back electromotive force into the self-holding circuit, and the resistance value of the heater 3 can be determined mainly from the viewpoint of securing the self-holding current, making the design easier. This has the excellent effect of making work much easier.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a conventional automatic return type thermal protector. In the figure, 3...heater, 4, 5...contact, 6...bimetal. FIGS. 1A and 1B show the configuration of a conventional manual reset type thermal protector. In the figure, 4... thermistor, 5... switch, 6... power source, 7... load, 8... bimetal contact (make contact), 9... resistor for current limiting. FIG. 2 shows the structure of a thermal protector which is an embodiment of this invention. In the same figure, 3... heater, 4, 5, 8,
9...Contact, 6...Bimetal. FIG. 3 shows an example of the use of a thermal protector which is an embodiment of this invention. In the figure, 11...power supply, 12...power switch, 13...main winding.

Claims (1)

[Claims for Utility Model Registration] A heater 3 that generates heat when a current passes through it; a heat-sensitive deformable body 6 that deforms in response to the heat generated by the heater 3; and a heat-sensitive deformable body 6 that generates heat when a load current passes through a load circuit. In a thermal protector having break contacts 4 and 5 that are opened by deformation of a heat-sensitive deformable body 6 in response to heat from a heater 3, and disconnect the load from the power source and cut off the load current, A thermal protector characterized in that it is equipped with make contacts 8 and 9 that close in conjunction with interruption of load current in a load circuit and allow the self-holding current to pass through the self-holding circuit including the heater 3.