JP3148914B2 - Electric water heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric water heater for heating and keeping water contained in a container.

[0002]

2. Description of the Related Art In recent years, electric water heaters have been widely used, but there is a problem in controlling high-temperature heat retention near a boiling point.

[0003] Hereinafter, a conventional electric water heater will be described with reference to the drawings. FIG. 6 is a block diagram showing a configuration of a conventional electric water heater. Generally, an electric water heater is configured to keep water at a predetermined temperature after boiling water.

In FIG. 6, 1 is a main body of an electric water heater, 2 is a container having an upper surface opening provided inside the main body 1, 3
Is a cover for covering the upper part of the container 2, 4 is a heater serving as a heating means for heating water inside the container 2, 5 is a heat keeping heater which is a heat keeping means for heating and keeping the water, and 6 is a heat keeping means which is inside the container 2. A temperature sensor for detecting a water temperature, 7 a temperature detecting means for detecting a water temperature based on a signal from the temperature sensor 6, a heating energizing means 8 for energizing the heating heater 4 and the heat retaining heater 5, 9
Is a heating means for controlling the power supply to the heating heater 5; 10 is a boiling detecting means for detecting boiling when the temperature rise rate of the temperature data of the temperature detecting means is less than a predetermined value; Means for controlling the heat and heat retention for controlling the means 9; 13 means for setting reboil for setting reboil; 14
Is a heat retaining temperature setting means for setting a heat retaining temperature, and 15 is a display means for displaying an operation state. The boiling detecting means 10
And the heating and heat keeping control means constitute a control means 17. The reboil setting means 13 is for setting when the water is to be boiled again in the warm state, and is constituted by, for example, a push switch. Also, the display means 15
A boiling LED 15a that indicates that the water is being heated,
High temperature insulation LED that indicates that the temperature is maintained at about 95 ° C
15b and 85 indicating that the temperature is kept at about 85 ° C.
It is composed of a warming LED 15c and a 70-warming LED 15d that indicates that the temperature is kept at about 70 ° C.

FIG. 7 is a circuit diagram showing an electric configuration of a conventional electric water heater. In the figure, a microcomputer 20 constitutes a main part of a control means 17 by a program operation, controls a relay 8 which is a heating current applying means and a triac 9 which is a heat keeping current applying means, and energizes the heating heater 4 and the heat keeping heater 5. Is determined. When boiling the water, the microcomputer 20 operates the relay 8 to energize the heater 4 and also operates the triac 9 to energize the heater 5. To keep the water warm after boiling, the microcomputer 20 operates the triac 9 to energize the warming heater 5.

On the other hand, a resistor 7a is connected in series to a temperature sensor 6 mounted in pressure contact with the container 2, the voltage at the connection point is input to the A / D converter, and the output is input to the microcomputer 20. These are the temperature detecting means 7
Is composed. Since the resistance value of the temperature sensor 6 changes depending on the temperature of the water in the container 2, the voltage determined by the resistance ratio between the temperature sensor 6 and the resistor 7a changes depending on the temperature. This voltage is converted into a digital value by the A / D converter 7d and input to the microcomputer 20 as temperature data. The voltage determined by the resistor 7b and the resistor 7c is also input to the A / D converter 7d, and determines the temperature (about 95 ° C.) at the time of high temperature keeping. The voltage determined by the resistor 7e and the resistor 7f is the temperature at the time of keeping the temperature at 85 (about 85
° C). Further, a resistor 7g and a resistor 7h
Is determined when the temperature is kept at 70 (about 70 ° C.). Also, a reboil switch 13 serving as a reboil setting means is provided.
The warming switch 14 as warming temperature setting means is connected to the input of the microcomputer 20, and the display means 15 is connected to the output of the microcomputer 20.

[0007] The interrelationship and operation of the above components will be described. When heating the water in the container 2 for the first time, the heating and heat keeping control means 12 controls the power supply to the heater 4 and the heat keeping heater 5 through the heating and electricity supplying means 8 and the heat and electricity keeping means 9 by the output of the temperature detecting means 7. Heat. Boiling detection means 1
When the detection of boiling is input by 0, energization control of the heat retaining heater 5 is performed so as to keep the temperature at the temperature set by the heat retaining setting means 14. When the re-boiling setting means 13 is set, the heating heater 4 and the warming heater 5 are controlled again through the heating energizing means 8 and the warming energizing means 9 based on the temperature data from the temperature detecting means 7 again, so that the water in the container 2 is discharged. Heat until boiling.

FIG. 8 is a characteristic diagram showing a temperature detecting method.
In the figure, the solid line indicates temperature data from the temperature sensor, and the broken line indicates water temperature. The time required for the temperature data from the temperature sensor 6 to rise by a predetermined temperature Δθ (for example, 0.5 ° C.) after the heater 4 and the heat retaining heater 5 are energized (hereinafter, referred to as a predetermined temperature rise time) Measure Δt. This time Δt gradually increases as the water temperature approaches the boiling point. The current value of t {tb is the value immediately after the start of heating}
When the predetermined time is longer than a predetermined time, the microcomputer 2
0 detects that the water has boiled. As described above, the temperature θ1 indicated by the temperature data when the boiling is detected is characterized in that the temperature θ1 is lower than the boiling point temperature. Needless to say, the predetermined temperature Δθ is not limited to 0.5 ° C.

After detecting the boiling, when the temperature is kept high, the resistance ratio between the temperature sensor 6 and the resistor 7a connected in series is
The triac 9 is operated so as to keep the temperature at the high temperature keeping temperature (about 95 ° C.) while comparing the resistance ratio between the resistor 7b and the resistor 7c corresponding to the high temperature keeping. That is, the boiling is detected by the temperature change rate, but the heat retention control is executed by the temperature value.

[0010]

In such a conventional electric water heater, there is a problem that when the heat retention temperature is set to be high in an area having a low atmospheric pressure such as an altitude, the boiling point may be lowered and the boiling may be continued. is there. That is, since the heat retention control after boiling is performed based on the temperature value, when the boiling point is lower than the set heat retention temperature, even if heating by the heat retention heater does not reach the set heat retention temperature, the boiling is continued. As described above, since the heat retention temperature is fixedly set by the resistance ratio of the resistor, it cannot be set arbitrarily according to the current boiling point, and therefore, it is not possible to provide high-temperature hot water close to the boiling point. There was a problem.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an electric water heater that can keep the temperature close to the boiling point.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a container for containing a liquid, a heating unit for heating the liquid in the container, and a heat retaining unit for heating and heating the liquid. Heating means for energizing the heating means to heat the liquid, heating and energizing means for energizing the heating means to heat and maintain the temperature, and temperature detection for detecting the temperature of the liquid and outputting temperature data Means, and control means for controlling the operation of the apparatus, wherein the control means detects the boiling of the liquid based on the time rise rate of the temperature value indicated by the temperature data output by the temperature detection means, and then detects the temperature. Stabilizing heating for stabilizing data is performed, temperature data at the time when the stabilizing heating is completed is input from the temperature detecting means, and a predetermined value is obtained from a temperature value indicated by the input temperature data. Only an electric water heater controlled to kept at low temperatures.

[0013]

According to the present invention, in the above configuration, the control means detects the boiling of the liquid based on the time rise rate of the temperature value indicated by the temperature data output from the temperature detection means, and subsequently stabilizes the temperature data. Is performed, and the temperature data at the time when the stabilized heating is completed is inputted from the temperature detecting means, and the temperature is controlled at a temperature lower than the temperature value indicated by the inputted temperature data by a predetermined value. The temperature value indicated by the temperature data after stabilization heating gives the boiling temperature in the current environment, and by setting the heat retention temperature based on the boiling temperature and keeping the temperature, the situation where the boiling continues does not occur, Enables close insulation.

[0014]

【Example】

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. Note that the same components as those of the conventional example shown in FIG. 6 are denoted by the same reference numerals, and detailed description is omitted.
The difference between the present embodiment and the conventional example is that the control means 17 includes the temperature determination means 16, determines the temperature value at the time of boiling, and performs the heat retention control based on the determined temperature. Control means 1
Needless to say, the boiling detecting means 10, the heating and heat controlling means 12 and the temperature determining means 16 in 7 can be realized by a program operation of a microcomputer.

The interrelationship and operation of the above components will be described. In this embodiment, the temperature determining means 16 outputs a signal for controlling the heat-retaining energizing means 9 to the heating and heat-retaining control means 12 so as to energize the heat-retaining heater 5 for a predetermined time after detecting the boiling by the boiling detecting means 10. Then, the detected temperature of the temperature detecting means 7 after the predetermined time is inputted. The heating / warming control means 12 performs the same operation as that of the conventional example at the time of boiling water, and controls the warming and energizing means 9 so that the temperature determining means 16 keeps the temperature at a predetermined temperature lower than the input temperature at the time of warming.

FIG. 2 is a flowchart showing the heat retaining processing operation of the control means 17 in this embodiment. After the power supply is turned on, in step 100, the heater 4 and the heat retaining heater 5 are energized to start heating, and a predetermined temperature rise time, for example, a time Δtn required to rise by 0.5 ° C. is measured. At 101, it is checked whether or not it is equal to or longer than the previous predetermined temperature rise time Δtn-1. If Δtn is smaller than Δtn-1, it is determined that the temperature has not risen, and the routine returns to step 100. If Δtn is equal to or larger than Δtn−1, the process proceeds to step 102 to check whether the measurement has been performed four times, and returns to step 100 until the measurement is performed four times. When the measurement is performed up to four times, the process proceeds to step 103, and Δt2 to Δt4
ま で t = △ t2 + △ t3 + △ t4 is stored. Next, at step 104, the predetermined temperature rise time Δt ′
Is measured, and the routine proceeds to step 105, where Δt ′ is the above-mentioned Δ
It is checked whether it is not less than t. If Δt ′ is smaller than Δt, the process returns to step 104. If Δt ′ is equal to or more than Δt, the process proceeds to step 106, and boiling is detected.
The information is given to the temperature determining means 16. Note that the above-described boiling detection processing is performed by the boiling detection means 12 in the control means 17.
Can be performed by

Upon input of the boiling detection information, the temperature determining means 16 instructs the heating and heat keeping control means 12 in step 107 to energize only the heat keeping heater 4 for a predetermined time. The energization for the predetermined time is an energization for stabilizing the temperature data of the temperature sensor 6. After a lapse of a predetermined time, the flow shifts to step 108 to take in the temperature θ4 at that time.
Instruct 2 to keep the temperature of the temperature sensor 6 at a temperature several degrees lower than the temperature θ4 (θ4−Δθ4).

FIG. 5 is a characteristic diagram showing the relationship between elapsed time and temperature in this embodiment. FIG. 5A shows a state when the amount of water is small, and FIG. 5B shows a state when the amount of water is large. In the figure, the solid line is the temperature data value output by the temperature sensor 6,
The dashed line indicates the actual water temperature. Heater 4 and heat retaining heater 5
When the water at normal temperature is heated to the boil by energizing the water, a temperature difference occurs between the water temperature and the temperature indicated by the temperature sensor 6, as shown in FIG. As shown in (1), it is remarkable when the amount of water is small. When the water boils, the boiling detection based on the temperature change rate can follow relatively quickly, but the value of the water temperature itself is detected lower. Therefore, the temperature data at the time when boiling is detected is not immediately used as the boiling temperature. In order to solve this problem, in the present embodiment, the temperature difference between the temperature given by the temperature sensor 6 and the actual water temperature is determined by energizing the heat retaining heater 5 for a predetermined time following the detection of boiling, regardless of the amount of water. The temperature difference is stably kept within the predetermined temperature difference Δθ5. It is needless to say that the predetermined time for energizing the heat retaining means for the stabilizing heating can be set to an appropriate value in consideration of the volume of the target container and the volume of the water actually contained.

As described above, according to this embodiment, the temperature value indicated by the temperature sensor can be stabilized to indicate the water temperature by the stabilization heating in which the heating is performed by energizing the heat retaining heater for a predetermined time after the detection of boiling. Also, by taking in the temperature value at the time when the predetermined time has passed, the taken-in temperature value is very close to the actual boiling point temperature in the current environment, and the temperature is kept based on that temperature. There is no occurrence of a situation in which the boiling is continued without keeping the heat retention temperature at the actual boiling point temperature, and the heat retention close to the boiling point temperature is also possible.

(Embodiment 2) Hereinafter, a second embodiment of the electric kettle of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment, and a detailed description thereof will be omitted. The difference between the present embodiment and the first embodiment lies in the heat retention processing operation of the control means 17.

In the present embodiment, the temperature determining means 16
After the boiling is detected by the boiling detecting means 10, the temperature keeping means 5 is kept until the temperature change rate from the temperature detecting means 7 becomes a predetermined value or less.
A signal for controlling the heat-retaining and energizing means 9 is supplied to the heating and heat-retaining control means 12 so that power is supplied to the heating and heat-retaining control means 12, and the temperature detected by the temperature detecting means 7 when the temperature change rate falls below a predetermined value is taken in.

The operation of the above configuration will be described. FIG. 3 is a flowchart showing the heat retention processing operation of the present embodiment. Steps 100 to 1 in FIG.
The boiling detection processing up to 06 is the same as the processing shown in FIG. 2, and a detailed description thereof will be omitted. In step 110, the temperature determination means 16 provided with the information on the detection of boiling in step 106 from the boiling detection means 10 instructs the heating and heat keeping control means 12 to energize only the heat keeping heater 5, and proceeds to step 111. And the predetermined temperature rise time △ tm
Is measured, and it is checked in step 112 whether or not Δtm is equal to or more than a predetermined value. If Δtm is smaller than the predetermined value, the process returns to step 111 and repeats the same operation.
Is greater than or equal to the predetermined value, it is determined that the temperature data of the temperature sensor
Then, the process goes to step 109 to instruct the heating and heat keeping control means 12 to keep the temperature of the temperature sensor 6 at a temperature several degrees lower than the temperature .theta.4 (.theta.4 -.DELTA..theta.4). Note that the heat retaining state in this embodiment is the same as the state shown in FIG.

As described above, according to this embodiment, it is determined whether or not the temperature data is stabilized by the stabilization heating in which the predetermined temperature rise time after the detection of the boiling becomes longer than the predetermined value. Because heating is directly detected by the change rate, the stabilization heating time according to the amount of water, etc.,
Stabilized heating can be performed more effectively than heating for a predetermined period of time in the first embodiment. Further, as in the first embodiment, the situation where the boiling continues does not occur, and the temperature can be kept close to the boiling point.

Embodiment 3 Hereinafter, a third embodiment of the electric kettle of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment, and a detailed description thereof will be omitted. The difference between the present embodiment and the first embodiment lies in the heat retention processing operation of the control means 17.

In the present embodiment, the temperature determining means 16
After the boiling is detected by the boiling detecting means 10, a signal for controlling the heat-retaining and energizing means 9 is supplied to the heating and heat-retaining control means 12 so that the heat-retaining means 5 is energized, and a predetermined temperature rise time of the temperature detected by the temperature detecting means 7 is obtained. Further, when the predetermined temperature rise time at the elapse of the predetermined time becomes equal to or more than a certain time, the temperature detected by the temperature detecting means 7 is taken in.

The operation of the above configuration will be described. FIG. 4 is a flowchart showing the heat retention processing operation of this embodiment. Note that Step 100 to Step 1 in FIG.
The boiling detection processing up to 06 is the same as the processing shown in FIG. 2, and a detailed description thereof will be omitted. In step 113, the temperature determining means 16 provided with the information on the detection of boiling in step 106 from the boiling detecting means 10 instructs the heating and heat keeping control means to energize only the heat keeping heater 5,
The process proceeds to step 114 and waits for a predetermined time.
A predetermined temperature time Δtm of the temperature data is measured. Next, the process proceeds to step 116 and waits for a predetermined time. When the predetermined time has elapsed, the process proceeds to step 117 to measure the predetermined temperature rise time tl. Next, step 118
Then, it is checked whether or not the value tl is equal to or more than a predetermined multiple M · tm of the value tm. If tl is smaller than M · tm, the process returns to step 116 to repeat the same operation, and tl
When M is equal to or more than M · tm, the routine proceeds to step 108, where it is determined that the temperature data of the temperature sensor 6 has become stable, and the temperature data θ4 at that time is taken. Then step 109
Then, the heating and heat control means 12 is instructed to keep the temperature at a temperature several degrees lower than θ4 (θ4-△ θ4).

As described above, according to the present embodiment, the predetermined temperature rise time at the time when the predetermined time elapses is longer than the predetermined temperature rise time of the temperature detected by the temperature detecting means after the boiling detection. Heating is performed until the temperature output by the temperature detection means has stabilized, and the temperature is output while the temperature is being monitored. I can do it for sure. Also, the situation where boiling continues does not occur,
As in the first and second embodiments, it is possible to keep the temperature close to the boiling point.

Embodiment 4 Hereinafter, a fourth embodiment of the electric kettle of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment, and a detailed description thereof will be omitted. The difference between the present embodiment and the first embodiment lies in the heat retention processing operation of the control means 17.

In this embodiment, the temperature determining means 16
After the boiling is detected by the boiling detecting means 10, a signal for controlling the heating energizing means 8 so that the heating means 4 is intermittently energized for a predetermined time is output to the heating and heat keeping controlling means 12, and the temperature detecting means 7 after the predetermined time is output from the temperature detecting means 7. Enter the detected temperature of. The heating and keeping control means 12 performs the same operation as the conventional example at the time of boiling water,
At the time of keeping the temperature, the temperature deciding means 16 controls the heat keeping energizing means so as to keep the temperature at a predetermined temperature lower than the input temperature.

In the heat retention processing operation of the present embodiment, the heater 4 is intermittently turned on instead of turning on the heat retention heater 5 in step 107 of the flowchart shown in FIG. Other operations are the same as those in the first embodiment, and a detailed description thereof will be omitted. In this way, by conducting the heater 4 intermittently for a predetermined time, the temperature can be stabilized more quickly than in the means of the first embodiment.

As described above, according to the present embodiment, the heating means is intermittently energized for a predetermined time to stabilize the heating, so that the heating can be performed with higher power than the heating means, and the temperature detecting means outputs. Temperature data can be stabilized more quickly. Further, as in the case of the first to third embodiments, the situation where the boiling continues does not occur, and the temperature can be kept close to the boiling point.

Embodiment 5 Hereinafter, a fifth embodiment of the electric kettle of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment, and a detailed description thereof will be omitted. The difference between the present embodiment and the first embodiment lies in the heat retention processing operation of the control means 17.

In the present embodiment, the temperature determining means 16
After the boiling is detected by the boiling detecting means 10, the heating means 4 is turned on until the temperature change rate from the temperature detecting means 7 becomes a predetermined value or less.
A signal for controlling the heating and energizing means 8 so as to perform intermittent energization is output to the heating and heat keeping control means 12, and the detected temperature from the temperature detecting means 7 when the temperature change rate becomes equal to or less than a predetermined value is input.

The heat retention processing operation of this embodiment is similar to the heat retention heater 5 in step 110 of the flowchart shown in FIG.
Is a means for intermittently energizing the heater 4 instead of energizing. The other processing is the same as the processing of the second embodiment shown in FIG. 3, and a detailed description will be omitted. The effect of quickly stabilizing the temperature by intermittently energizing the heater 4 instead of energizing the heat retaining heater 5 is the same as that of the fourth embodiment, and the other effects are the same as those of the second embodiment.

As described above, according to the present embodiment, after the boiling, the heating means is intermittently energized until the temperature change rate becomes equal to or less than the predetermined value to stabilize the heating. Temperature data can be stabilized accurately and quickly. Further, as in the case of the first to fourth embodiments, the situation where the boiling continues does not occur, and the temperature can be kept close to the boiling point.

Embodiment 6 Hereinafter, a sixth embodiment of the electric kettle of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment, and a detailed description thereof will be omitted. The difference between the present embodiment and the first embodiment lies in the heat retention processing operation of the control means 17.

In this embodiment, the temperature determining means 16
After the boiling detecting means 10 detects the boiling, a signal for controlling the heating energizing means 8 to perform the intermittent energizing of the heating means 4 is output to the heating and heat keeping controlling means 12, and a predetermined time after the boiling detecting of the temperature detecting means 7 has elapsed. The detected temperature from the temperature detecting means 7 is input when the predetermined temperature rise time after the elapse of the predetermined time becomes equal to or more than a certain ratio with respect to the subsequent predetermined temperature rise time.

In the heat retaining process of this embodiment, the heater 4 is intermittently energized instead of energizing only the heater 5 in step 113 in the flowchart shown in FIG.
The temperature of the temperature sensor is quickly stabilized with higher power. Other processes are the same as those in the flowchart shown in FIG.

As described above, according to the present embodiment, the time when the predetermined temperature rise time after the elapse of the predetermined time becomes more than a certain ratio times the predetermined temperature rise time after the elapse of the predetermined time after the detection of boiling. Up to this time, the heating means is intermittently energized to stabilize the heating, whereby the temperature data output by the temperature detecting means can be stabilized with higher accuracy and speed. Further, as in the case of the first to fifth embodiments, the situation where the boiling continues does not occur, and the temperature can be kept close to the boiling point.

[0040]

As is apparent from the above description, the present invention provides a container for containing a liquid, a heating means for heating the liquid in the container, a heating means for heating and heating the liquid, A heating energizing unit that energizes a heating unit to heat the liquid, a heat retaining energizing unit that energizes the heating unit to heat and maintain the temperature, a temperature detecting unit that detects a temperature of the liquid and outputs temperature data, Control means for controlling the operation of the apparatus, wherein the control means stabilizes the temperature data after detecting the boiling of the liquid based on a time rise rate of the temperature value indicated by the temperature data output by the temperature detection means. The temperature data at the time when the stabilized heating is completed is input from the temperature detecting means, and the temperature is lower by a predetermined value than the temperature value indicated by the input temperature data. By controlling so as to keep the temperature in the water, the water is continuously heated even after boiling, and the stabilized heating is performed.The detected temperature output by the temperature detecting means is stabilized, and the temperature is several degrees lower than the stable detected temperature. Because it keeps warm,
Even at high altitudes, it is possible to keep warm without causing a situation where boiling continues, and to be closer to the boiling point, for example, (boiling point−
2) Since the temperature can be kept at a temperature of ° C., hot water having a higher temperature can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an electric water heater according to the present invention.

FIG. 2 is a flowchart showing a heat retention processing operation of the first embodiment of the electric water heater of the present invention.

FIG. 3 is a flowchart showing a heat retaining operation of the second embodiment of the electric water heater of the present invention.

FIG. 4 is a flowchart showing a heat retaining operation of an electric water heater according to a third embodiment of the present invention.

FIG. 5 is a characteristic diagram showing an operation of the embodiment of the electric kettle of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional electric water heater.

FIG. 7 is a circuit diagram showing an electric configuration of a conventional electric water heater.

FIG. 8 is a characteristic diagram showing the operation of a conventional electric water heater.

[Explanation of symbols]

 2 Container 4 Heater (heating means) 5 Heating heater (heating means) 6 Temperature sensor (temperature detecting means) 7 Temperature detecting means 8 Heating means 9 Heating means 17 Control means

Claims (7)

(57) [Claims] 1. A container for accommodating a liquid, a heating unit for heating the liquid in the container, a heating unit for heating and heating the liquid, and a heating and energizing unit for energizing the heating unit to heat the liquid. Means, a heat-retaining energizing means for energizing the heat-retaining means to heat and maintain the temperature, temperature detecting means for detecting the temperature of the liquid and outputting temperature data, and control means for controlling the operation of the device, The control means detects the boiling of the liquid based on the time rise rate of the temperature value indicated by the temperature data output by the temperature detection means, and then performs the stabilization heating for stabilizing the temperature data, and performs the stabilization heating. An electric water heater that inputs the temperature data at the point of time when the operation is completed from the temperature detecting means and controls the temperature to be maintained at a temperature lower by a predetermined value than the temperature value indicated by the input temperature data. 2. The electric water heater according to claim 1, further comprising control means for controlling the heating means to carry out the stabilizing heating by supplying electricity for a predetermined time. 3. A control means for controlling to perform stabilized heating by energizing the heat retaining means until a time change rate of a temperature value output from the temperature detecting means reaches a predetermined value or less. An electric kettle as described. 4. Control is performed such that stabilized heating is performed by energizing the heat retaining means until a predetermined temperature rise time at which a predetermined time elapses after the detection of boiling reaches a predetermined time or more. The electric water heater according to claim 1, further comprising control means for performing the operation. 5. The electric water heater according to claim 1, further comprising control means for controlling the heating means to perform stabilized heating by intermittently supplying electricity for a predetermined time. 6. A control means for controlling the heating means to perform stabilized heating by intermittently energizing the heating means until a time change rate of a temperature value output from the temperature detecting means becomes a predetermined value or less. An electric kettle as described. 7. Stabilized heating is performed by intermittently supplying current to a heating means until a predetermined temperature rise time at which a predetermined time elapses after the detection of boiling reaches a predetermined time or more. The electric water heater according to claim 1, further comprising control means for controlling.