JP2005331127A - Electric water heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in a water level sensor of a conventional electric water heater that false judgement may occur because of the attachment of impurities between an electrode and a hot water storage tank, as DC voltage is applied between the electrode placed at a position higher than a heater and the hot water tank. <P>SOLUTION: This electric water heater comprises the water storage tank 1, an electric heating element 6 having a heat generating part 6A for converting electric power into the heat, and a conductive protecting part 6B electrically insulated from the heat generating part 6A and covering the heat generating part 6A, the electrode 10 mounted on the position higher than the electric heating element 6 inside of the hot water storage tank 1 in a state of being electrically insulated, and a water level detecting means 11 having a DC power source 11A for applying DC voltage between the electrode 10 and the protecting part 6B to lower electric potential of the protecting part 6B, and detecting the existence of the water at the position of the electrode 10 on the basis of the variation of electric resistance between the electrode 10 and the protecting part 6B. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric water heater that converts electric power into heat to boil hot water.

  Electric water heaters are used to boil hot water using cheap electricity at midnight and store the boiled water in a water storage tank so that hot water can be used in baths, washrooms, kitchens, and the like. The water tank of the electric water heater is always filled with water, but there is no water in the water tank after checking the water tank or immediately after installing the electric water heater. When the heater of the electric water heater is energized in the absence of water, it becomes so-called emptying. Doing so may damage the heaters of the electric water heater and so on. The electric water heater has a water detection sensor that detects that there is water in the water storage tank up to the position of the heater so that it does not air, and only energizes the heater when there is water.

  The water detection sensor detects the presence of water by utilizing the fact that the electrical resistance of water is very small compared to air. In the water detection sensor, an electrode is attached to the inside of the water storage tank at a position above the heater, and a direct current is passed through a resistor between this electrode and the water storage tank so that the potential of the electrode is higher than that of the water storage tank. Apply voltage. The magnitude of this resistance is set to a value larger than that of which there is a clear difference from the resistance of water. If there is no water between the electrode and the water tank, no current flows between the electrode and the water tank, and the voltage between the electrode and the water tank is almost the applied voltage. When water is present, current flows between the electrode and the water tank, and the voltage between the electrode and the water tank is close to zero. That is, the water detection sensor determines that water is present when the voltage between the electrode and the water storage tank is smaller than a predetermined value. (For example, see Patent Documents 1 to 4.)

Japanese Patent No. 002552962. Japanese Patent Laid-Open No. 05-001854. Japanese Patent No. 002552962. Japanese Patent Application Laid-Open No. 06-0034200.

  Since the water detection sensor of the conventional electric water heater is configured as described above, if the impurity adheres between the electrode and the water storage tank and the impurity contains water, the electrode is not immersed in water. It is misjudged that there is water at the electrode position. Measures are required to reduce the possibility of misjudgment.

  The electric water heater according to the present invention includes a water storage tank, a heat generating part that converts electric power into heat, and a conductive protection part that is electrically insulated from the heat generating part and covers the heat generating part. Is electrically insulated and attached to the inside of the water tank, and the water tank is electrically insulated and attached to a position above the electric body inside the water tank. An electrode, and a DC power source that applies a DC voltage between the electrode and the protection unit so that a potential of the protection unit is low, and the electrical resistance between the electrode and the protection unit changes due to a change in electrical resistance. Water detection means for detecting the presence of water up to the position of the electrode.

  The electric water heater according to the present invention includes a water storage tank, a heat generating part that converts electric power into heat, and a conductive protection part that is electrically insulated from the heat generating part and covers the heat generating part. Is electrically insulated and attached to the inside of the water tank, and the water tank is electrically insulated and attached to a position above the electric body inside the water tank. An electrode, and a DC power source that applies a DC voltage between the electrode and the protection unit so that a potential of the protection unit is low, and the electrical resistance between the electrode and the protection unit changes due to a change in electrical resistance. Since water detection means for detecting the presence of water up to the position of the electrode is provided, there is an effect of reducing the possibility of erroneous determination due to impurities attached to the electrode.

Embodiment 1 FIG.
The conceptual diagram explaining the structure of the electric water heater in this Embodiment 1 is shown in FIG. First, the components of the electric water heater related to the flow of water will be described. The electric water heater has a water storage tank 1 made of stainless steel or the like having excellent corrosion resistance, a water supply pipe 2 connected to the lower part of the water storage tank 1, and a pressure reducing valve 3 between the water supply pipe 2 and the water supply pipe. And a hot water supply pipe 4 connected to the upper part of the water storage tank 1 and a relief valve 5 in the middle of the hot water supply pipe 4.
FIG. 1 shows an electric water heater that uses a pressurized water storage tank 1. In the pressurization type water storage tank 1, the water storage tank 1 is sealed, water pressure is applied to the inside, and hot water is supplied by this water pressure. On the other hand, there is also an electric water heater that uses an open-type water storage tank 1 that does not seal the water storage tank 1. In an electric water heater that uses an open-type water storage tank 1, the water storage tank 1 is disposed at a position higher than a hot water supply location such as a kitchen, a bath, and a washroom, and hot water is supplied by a water head difference. In this specification, the electric water heater using the pressurized water tank 1 will be described, but the present invention can also be applied to the case where the open water tank 1 is used.

The water storage tank 1 is a tank for storing boiled hot water. The capacity of the water storage tank 1 is set to a size necessary and sufficient for the amount of hot water used per day. For this reason, the capacity of the water storage tank 1 varies depending on the usage conditions of the electric water heater, such as for large families, standard families, small families, and single persons. In the case of what is marketed in 2004, the maximum is about 550 liters. The outside of the water storage tank 1 is covered with a heat insulating material such as glass wool so that the accumulated hot water does not cool, and the outside of the heat insulating material is covered with a suitable surface member.
Since the specific gravity of water decreases as the temperature rises, the hot water is on the upper side and the water is on the lower side in the water storage tank 1. Therefore, the water supply pipe 2 is connected to the lower part of the water storage tank 1, and the hot water supply pipe 4 is connected to the upper part of the water storage tank 1. In the figure, the hot water is expressed in a thin pear-like shape, and the water is expressed in a dark pear-like shape.

Although not shown, there is a faucet at a hot water supply point at the tip of the hot water supply pipe 4. When the faucet at the hot water supply location is opened, the hot water comes out because the inside of the water storage tank 1 is pressurized. When hot water is discharged from the water storage tank 1 to the hot water supply pipe 4, the same amount of water is injected into the water storage tank 1 through the water supply pipe 2.
Some of the faucets at the hot water supply place take out the hot water from the hot water supply pipe 4 as it is, and some have a mixture of hot water and tap water.

The pressure reducing valve 3 is a valve for reducing the water pressure of the water supply so that the water pressure inside the water storage tank 1 becomes an appropriate value. The water pressure of the water supply varies depending on the location, but it is stipulated by the Ordinance of the Ministry of Health, Labor and Welfare that it is 150 kilopascals (≈1.48 atm) or more. On the other hand, the water pressure inside the water storage tank 1 is about 150 kilopascals for the high pressure type and about 85 kilopascals for the standard pressure type. The higher the water pressure in the water storage tank 1, the faster the hot water can be used. However, in order to increase the water pressure, it is necessary to make the stainless steel material of the water storage tank 1 thicker, resulting in an increase in cost and the price of the electric water heater. The water pressure inside the water storage tank 1 is determined by a trade-off between ease of use and cost.
When the internal pressure of the water storage tank 1 becomes higher than a predetermined value, the relief valve 5 removes water and water that has undergone volume expansion by boiling, dissolved air that has become gas due to an increase in water temperature, and the like with the water storage tank 1. A valve for escaping from the hot water supply pipe 4. With the relief valve 5, the pressure inside the water storage tank 1 can be maintained within a predetermined range.

  Next, other components of the electric water heater will be described. Inside the water storage tank 1, two heaters 6 with different heights are attached by metal flanges 7. An insulator packing 8 is sandwiched between the metal flange 7 and the water storage tank 1. A resin housing 9 having heat resistance such as PEEK, PPS, PES or the like is attached to the water storage tank 1 at a position above the upper metal flange 7. A metal electrode 10 having excellent corrosion resistance such as titanium, gold, or platinum is inserted into the housing 9, and the electrode 10 is attached to the inside of the water storage tank 1. The electrode 10 has a diameter of about 1 mm and a length that goes out of the water storage tank 1 is about 20 mm. Furthermore, the electric water heater also includes a water detection sensor 11 that is a water detection means for detecting the presence of water up to the position of the electrode 10, and a control circuit 12 that controls energization of the heater 6 based on the output of the water detection sensor 11. Have.

The lower heater 6 is a heater that is normally used, and the upper heater 6 is a heater that is used when boiling is increased. For example, when the remaining amount of hot water in the water storage tank 1 becomes a predetermined amount (for example, 75 liters) or less, the upper heater 6 is energized even if it is not at midnight power hours. It is to boil hot water of a capacity (for example, 150 liters) of the upper storage tank 1. In the case of a contract that uses electricity only in the midnight power hours, it cannot be heated up. Moreover, it can also set so that it may not boil. In order to cope with a day when a large amount of hot water that greatly exceeds the capacity of the water storage tank 1 is used, there is a model in which the entire water storage tank 1 can be heated up to be filled with hot water of a predetermined temperature.
The position of the upper heater 6 is a position where the amount of hot water to be heated becomes an appropriate amount. Since boiling is performed during the normal electricity bill time, if the amount of hot water to be heated is larger than an appropriate amount, hot water that is not used is boiled, and the hot water supply cost is increased. If the amount of hot water to be heated is less than an appropriate amount, there is a high possibility that the hot water will not catch up with the amount of hot water used and run out of hot water.

  The heater 6 is obtained by covering a nichrome wire 6A, which is a heat generating portion to which AC 200V is applied, with a copper U-shaped tube 6B, which is a protective portion. A switch 6C expressing energization of the heater 6 is provided between the AC power source 6D and the nichrome wire 6A. Between the nichrome wire 6A and the copper U-shaped tube 6B, magnesium oxide or the like is filled as an insulator. The copper U-shaped tube 6B is plated with nickel or the like to prevent rust. When viewed from above, the heater 6 has a U-shape, and when viewed from the side, the heater 6 appears to connect two horizontal lines with diagonal lines. The heater 6 extending horizontally from the metal flange 7 descends by a predetermined length obliquely downward inside the water storage tank 1 and extends horizontally again by a predetermined length. The reason why the heater 6 is slanted in the middle is to make the length of the heater 6 longer than the diameter of the water storage tank 1. When the heater 6 is lengthened, the surface area of the heater 6 that comes into contact with water increases, and water can be efficiently boiled.

The output of the heater 6 is to heat the water in the capacity of the storage tank 1 from the average water temperature in winter in a place where an electric water heater is used to a predetermined temperature (for example, about 90 ° C.) in 8 hours from 23:00 to 7:00. Make it large enough to do. Actually, since there is unusable hot water, energization of the heater is terminated when heating to a predetermined temperature is possible. The boiling water temperature can be set between a predetermined range (for example, about 90 ° C. to about 70 ° C.). This is because energy saving can be realized without boiling wasteful water by setting the boiling water temperature low at homes where the amount of hot water used is low.
The heater 6 is fixed to the metal flange 7 by brazing or the like. Since it is easy to corrode when different kinds of metals are joined, the metal flange 7 is made of copper plated with nickel or the like in order to prevent corrosion.

The water detection sensor 11 which is a water detection means detects that water exists up to the position of the electrode 10. The high pressure type electric water heater is required by law to install the water detection sensor 11, but the standard pressure type electric water heater is not required by law. In a standard pressure type electric water heater not equipped with the water detection sensor 11, the user determines whether the water storage tank 1 is full, and turns on the electric water heater.
In the water detection sensor 11, a DC power source 11A having a predetermined size E0 (for example, 5 volts), a switch 11B, a resistor 11C having a size R1 (for example, about 200 kΩ to 300 kΩ), and a size R2 (this embodiment 1) Then, a resistor 11D (same as R1) is connected in series, a terminal having a higher potential on one side of the resistor 11D is connected to the electrode 10, and a terminal having a lower potential is connected to the metal flange 7. The reason for lowering the potential of the metal flange 7 is to protect the metal flange 7 and the heater 6 as will be described in detail later.
Here, the switch 11 </ b> B is a switch that expresses whether or not the water detection sensor 11 checks whether or not water is present. Normally, the switch 11B is off, and the case where the water level check is executed is entered.

The water detection sensor 11 has a comparator 11E that compares the voltage VC between the electrode 10 and the metal flange 7 with a predetermined threshold value Vt, and the output of the comparator 11E becomes the output of the water detection sensor 11. It is assumed that there is water when VC is smaller than Vt, and there is no water when it is not.
The control circuit 12 checks whether water is present up to the position of the electrode 10 by the water detection sensor 11 at the start of energization of the heater 6 and at a predetermined period during energization (for example, 3 minutes or 5 minutes). The heater 6 is energized only when it is present. The reason for checking the presence / absence of water even during energization is to stop energization of the heater 6 when the water in the water storage tank 1 or piping is damaged and the water inside the water storage tank 1 is rapidly reduced.

Next, the operation will be described. If the electric water heater is used for the first time after installation, or if it is not used for a long time and then used again, the following procedure is performed.
First, since there is no water inside the water storage tank 1, water is introduced into the water storage tank 1 through the water supply pipe 2. If either the relief valve 5 or the faucet at the hot water supply point is open, the air inside the water tank 1 is discharged out of the water tank 1 by the supplied water, and the water level of the water tank 1 gradually rises. To do. The standard procedure differs depending on the model, but for example, it is as follows. Close the relief valve 5 and open only one faucet in the hot water supply area. When the water storage tank 1 is full and the air in the hot water supply pipe 4 and the hot water supply point is removed, water comes out from the open tap in the hot water supply point, so the tap is closed.

  Next, turn on the electric water heater and set the time of the electric water heater clock. Set any necessary settings such as boiling water temperature. If the user has done so far, the electric water heater will automatically operate thereafter. Usually, after the electric water heater is installed, a test operation is performed to confirm the operation. The details of the test operation are as follows. When the control circuit 12 checks the presence or absence of water with the water detection sensor 11 and detects that the water detection sensor 11 has water up to the position of the electrode 10, the water temperature at the upper part of the current tank is compared with the set water temperature and set. When there is a predetermined temperature difference with respect to the water temperature, energization of the upper heater 6 is started, the water above the upper heater 6 is heated to a set temperature, and when boiling is completed, the energization is stopped. . In this way, the water in the upper part of the tank can be boiled to confirm the operation after installation, and the water heater can be used from the day of installation. When the midnight power zone is reached, energization of the lower heater 6 is started in order to boil the water in the entire tank to the set temperature, and the boiling is completed within the midnight power zone.

  When air cannot be discharged from the inside of the water storage tank 1 for some reason and there is no water at the position of the electrode 10, the water detection sensor 11 does not detect the presence of water up to the position of the electrode 10. If an error occurs, the process is interrupted, and the user is informed that the water supply is not completed by the display on the remote controller installed in the kitchen or bathroom. Since this error is displayed until the water supply is completed, the test operation can be completed only after the water supply is completed by performing a procedure for releasing air. As a case where the air cannot be discharged from the inside of the water storage tank 1, a case where water supply is started with all the faucets and the relief valves 5 closed can be considered.

  A method in which the water detection sensor 11 detects that there is water up to the position of the electrode 10 will be described. The principle is that the equivalent resistance value between the electrode 10 and the metal flange 7 when water is present up to the position of the electrode 10 is much smaller than that when there is no water, so that the equivalent resistance value is reduced. Is detected. In the first embodiment, the reduction in the value of the equivalent resistance is detected by comparing the voltage VC between the electrode 10 and the metal flange 7 with a predetermined threshold value Vt.

An electrical equivalent circuit of the water detection sensor 11 is shown in FIG. FIG. 3 is a diagram for explaining a path through which a current flows inside the water storage tank 1, which is a source of this equivalent circuit. This equivalent circuit replaces the water tank 1 made of stainless steel and water with a resistance of a predetermined size, and expresses the water level inside the water tank 1 with a plurality of switches. Since both the surface of the heater 6 and the metal flange 7 are made of copper having a very high conductivity, the electrical resistance is ignored and the surface of the heater 6 and the metal flange 7 are set to the same potential.
In FIG. 3, the upper part of the water storage tank 1 is enlarged and displayed. When a voltage is applied between the electrode 10 and the metal flange 7 by the DC power source 11A and the inside of the water storage tank 1 is filled with water, a path through which a current flows is indicated by a thick gray line. X shown in FIG. 3 is a path through the water storage tank 1. The portion of the water storage tank 1 on this route is dark gray. Y shown in FIG. 3 is a path that passes only water.

The meaning of the terminals in the equivalent circuit of FIG. 2 will be described. The terminal 11F corresponds to the electrode 10. The terminal 11G corresponds to the surface of the heater 6 and the metal flange 7. In the water storage tank 1, the portion close to the electrode 10 becomes the terminal 11 </ b> H, and the portion close to the metal flange 7 becomes the terminal 11 </ b> J.
Between the terminal 11H and the terminal 11J, there is a resistor 11K having a size RS (several Ω to several tens Ω) mainly corresponding to the stainless steel water tank 1. Between the terminal 11F and the terminal 11H, there is a resistor 11L having a size RW1 (several hundred Ω to several kΩ) corresponding to water, and a switch 11M. The switch 11M is turned on when there is water in the water storage tank 1 up to the position of the electrode 10, and is turned off otherwise. Between the terminal 11G and the terminal 11J, there is a resistor 11N having a size RW2 (about several hundred Ω to several kΩ) corresponding to water, and a switch 11P. The switch 11P is turned on when there is water in the water storage tank 1 up to the position of the upper heater 6, and is turned off otherwise.

  When the space between the electrode 10 and the surface of the heater 6 and the metal flange 7 is filled with water, as shown in FIG. 3, between the electrode 10 and the heater 6, the path X passing through the water storage tank 1 and only water. The path Y is formed in parallel. As can be seen from the fact that the path X in FIG. 3 has water portions on both sides with the water storage tank 1 in between, the resistor 11K, the resistor 11L, and the resistor 11N are in series in the equivalent circuit of FIG. The magnitude RS of the resistor 11K is a value that takes into account that the path Y is in parallel. In addition, since stainless is much easier to flow electricity than water, RS is approximately equal to the resistance value of the stainless steel water storage tank 1.

When there is water in the water storage tank 1 up to the position of the electrode 10, both the switch 11M and the switch 11P are turned on. That is, between the terminal 11F and the terminal 11G, a resistor 11K having a size RS, a resistor 11L having a size RW1, a resistor 11N having a size RW2, and a resistor 11D having a size R2 are connected in parallel. . When the size of the equivalent resistance between the terminal 11F and the terminal 11G is RT, RT is as follows.
RT = (R2 × (RS + RW1 + RW2)) / (R2 + RS + RW1 + RW2) (Formula 1)
When the switch 11B is turned on in this state, the current I flowing through the resistor 11C having the size R1 can be calculated by the following equation.
I = E0 / (R1 + RT) (Formula 2)
From Ohm's law, the voltage VC can be calculated by the following equation.
VC = RT × I = E0 × (RT / (R1 + RT)) (Formula 3)

When there is no water in the water storage tank 1 up to the position of the electrode 10, at least the switch 11M is turned off. Also assume that R2 = R1 and E0 = 5 volts. Therefore, I and VC can be calculated as follows.
I = E0 / (R1 + R2) (Formula 4)
VC = R2 × I = E0 × (R2 / (R1 + R2)) = 2.5 volts (Formula 5)
Here, regarding (RS + RW1 + RW2) /R2=0.01 regarding the magnitude of RS + RW1 + RW2, RT is as follows from (Equation 1).
RT = (0.01 / 1.01) × R2 = 0.0099 × R2 (Formula 6)
Substituting (Equation 6) and R2 = R1 into (Equation 3) gives the following.
VC = E0 × (0.0099 / 1.0099) = 0.0045 volts (Formula 7)

It can be seen that VC is about 1/55 compared to (Equation 5) when there is no water up to the position of the electrode 10 in the water storage tank 1. When the electrical resistance of water is larger and (RS + RW1 + RW2) /R2=0.1, RT and VC are similarly as follows. In this case, when R1 = 200 kΩ, RW1≈RW2≈10 kΩ. This means that it is much more resistant than normal tap water. If it is normal tap water, it may be considered that (RS + RW1 + RW2) / R2 <0.1.
RT = (0.1 / 1.1) × R2 = 0.0909 × R2 (Formula 8)
VC = E0 × (0.0909 / 1.0909) = 0.417 volts (Formula 9)

  From (Equation 7) and (Equation 9), if Vt is set to a small value with a sufficient margin than 2.5 volts, for example, 1.5 volts, when VC is compared with Vt, Whether or not there is water up to the position of the electrode 10 can be determined. This means that even if E0 drops from 5 volts to 4 volts, VC when there is no water is 2 volts, which is larger than Vt which is 1.5 volts, and it can be correctly determined that there is no water. The VC in the presence of water is about 0.4 volts, which is clearly smaller than 1.5 volts, even though the water resistance is fairly large (Equation 9).

  Thus, if E0, R1, R2, and Vt are set appropriately, the water detection sensor 11 can correctly determine whether or not there is water up to the electrode 10 by comparing VC and Vt. A circuit configuration other than that shown in FIG. 1 may be used as long as water can be detected up to the position of the electrode 10 and the electrical resistance between the metal flange 7 and the copper U-shaped tube 6B can be detected.

Now, it will be described that the water detection sensor 11 of the electric water heater according to the present invention can reduce the possibility of impurities being attached and erroneous determination. Here, when the switch on the equivalent circuit in FIG. 2 is always turned on due to the adhesion of impurities or the like is referred to as defective conduction.
In the equivalent circuit of FIG. 2, there are two switches 11M and 11P that represent the presence of water. Here, the defective conduction of the switch 11M means that impurities adhere to the electrode 10 and the defective water conduction occurs between the water storage tanks 1. In addition, the defective conduction of the switch 11P means that impurities adhere to the boundary portion between the metal flange 7 and the water storage tank 1 and conduct poorly. On the other hand, in the conventional water detection sensor 11 that compares the voltage between the water storage tank 1 and the electrode 10 with a threshold value, there is only one corresponding to the switch 11M.

An operation when the switch 11M and the switch 11P are defectively connected will be described. FIGS. 4 to 6 are diagrams for explaining the operation when the switch 11M and the switch 11P are defectively connected. FIG. 4 shows the case where only the switch 11M is defectively connected, FIG. 5 shows the case where only the switch 11P is defectively connected, and FIG. 6 shows the case where the switch 11M and the switch 11P are badly connected.
In FIG. 4, the case where water has come to the lowest part of the upper U-shaped metal flange 7 and the U-shaped pipe 6B made of copper at the lowest position is shown. In this state, the water detection sensor 11 erroneously determines that there is water up to the position of the electrode 10. In addition, A shown in the figure is an impurity attached to the electrode 10. In this case, since the heater 6 used at night on the lower side is completely submerged in water, the lower heater 6 cannot be scooped up.
Even if the upper heater 6 is energized, a part of the upper heater 6 is in contact with water, and the heater 6 generated by a conventional water detection sensor is not in contact with water. Because the amount of generated heat moves to water, the temperature does not rise excessively. Further, as a possibility of energizing the upper heater 6 in the state of FIG. 4, there is a case where the water tank 1 in a full state is damaged, the water inside the water tank 1 leaks and the water level is lowered. In that case, an error may be generated to stop the operation of the electric water heater, thereby preventing the heater 6 from being blown.

FIG. 5A shows a case where water has reached the position of the electrode 10, and FIG. 5B shows a case where the water level is lower than that of the electrode 10. In addition, B shown in the figure is an impurity adhering to the metal flange 7. Even if the switch 11P is defectively connected, the water detection sensor 11 normally determines that there is water up to the position of the electrode 10 in FIG. 5A, and in FIG. Determine that there is no water.
In FIG. 6, even when there is no water inside the water storage tank 1, the water detection sensor 11 erroneously determines that there is water up to the position of the electrode 10.
As described above, the water detection sensor 11 of the electric water heater according to the present invention may make an erroneous determination that leads to emptying of the heater 6 only when both the switch 11M and the switch 11P are defectively connected. However, the possibility that both the switch 11M and the switch 11P are defectively connected is much smaller than the case where the switch 11M is defectively connected in the conventional water detection sensor 11. That is, the possibility that the water detection sensor 11 of the electric water heater according to the present invention makes an erroneous determination is much smaller than that of the conventional one.

When electricity is passed through water, the water is electrolyzed, oxygen is generated at the anode, and hydrogen is generated at the cathode. The size R1 of the resistor 11C is sufficiently increased so that not much hydrogen and oxygen are generated. If R1 is 200 kΩ or more, there is a situation in which gas is not discharged from the water storage tank 1, and even if it is continuously used for 30 years or more, hydrogen and oxygen are less than half of the capacity above the electrode 10 of the water storage tank 1. Not accumulated. Providing the switch 11B and energizing it only when necessary also reduces the amount of electrolysis of water.
When the anode material has a higher ionization tendency than hydrogen, the anode melts instead of generating oxygen at the anode. In order to prevent the anode from melting, the anode is made of titanium, gold, platinum, etc., which has a lower ionization tendency and higher corrosion resistance than hydrogen. Since these metals are expensive, only a predetermined thickness from the surface may be plated with these metals.

Since the upper heater 6 is used as a cathode, there is an effect that only one electrode 10 needs to be used. Further, since the cathode does not melt, by using the heater 6 as a cathode, the heater 6 becomes an anode with respect to the water storage tank 1 or the electrode 10, and the possibility that the heater 6 melts and breaks down is reduced. Here, only the upper heater 6 is used as a cathode, but if both the two heaters 6 are used as cathodes, the heater 6 can be protected from melting. Even when there is only one heater 6, the heater 6 can be protected from melting.
The heater 6 becomes an anode with respect to the water storage tank 1 when static electricity is accumulated in the heater 6 or the like. There is a heater 6 whose life is extremely shorter than the standard life, and although it is not certain that the heater 6 becomes an anode with respect to the water storage tank 1 or the electrode 10 and melts, the life of the heater 6 is shortened. This is considered to be one of the factors.

The size of the resistor 11D is set so that the voltage VC in the absence of water is sufficiently large, so that the resistance 11D is equal to or greater than R1, or even if it is smaller than R1, several tens of percent of R1. Making R2 sufficiently larger than R1 has an effect that the voltage VC in the absence of water becomes closer to the voltage E0 of the DC power supply, and the threshold value Vt can be taken in a wider range. R2 may be infinite. However, when R2 is a finite value, there is an effect that it is possible to detect that a current flows when the switch 11B is turned on, and that a disconnection or the like has occurred.
The above also applies to other embodiments.

Embodiment 2. FIG.
The second embodiment is a case where the first embodiment is changed so that both of the two metal flanges 7 are the cathodes of the water detection sensor 11. The conceptual diagram explaining the structure of the electric water heater in this Embodiment 2 is shown in FIG. The difference from FIG. 1, which is the case of the first embodiment, is that the metal flange 7 of the lower heater 6 is also connected to the terminal having the lower potential of the resistor 11D having the size R2. The equivalent circuit in FIG. 2 is the same as that in FIG. 1 except that the condition for the switch 11P to enter is that the lowermost portion of the lower U-shaped tube 6B comes into contact with water.

According to the second embodiment, since both of the two heaters 6 do not become anodes with respect to the water storage tank 1 or the electrode 10, there is an effect that both the heaters 6 can be protected from melting. .
Even when there are three or more heaters 6, all the heaters 6 can be protected from melting if all the heaters 6 are used as the cathodes of the water detection sensor 11.

Embodiment 3 FIG.
The third embodiment is a case where the second embodiment is changed so that the housing 9 is attached to the upper metal flange 7. The conceptual diagram explaining the structure of the electric water heater in this Embodiment 3 is shown in FIG. The difference from FIG. 7, which is the case of the second embodiment, is that the housing 9 is attached to the upper metal flange 7 instead of the water storage tank 1. Similarly to the case of the second embodiment, the electrode 10 is located above the upper heater 6.

  Also in this third embodiment, since both the two heaters 6 do not become anodes with respect to the water storage tank 1 or the electrode 10, there is an effect that both the heaters 6 can be protected from melting.

It is a conceptual diagram explaining the structure of the electric water heater in Embodiment 1 of this invention. It is a figure explaining the equivalent circuit of the water detection sensor in Embodiment 1 of this invention. It is a figure explaining the path | route through which an electric current flows inside the water storage tank in Embodiment 1 of this invention. It is a figure explaining the operation | movement when only between the electrode and water storage tank in Embodiment 1 of this invention carries out defective conduction. It is a figure explaining the operation | movement when only between the metal flange and water storage tank in Embodiment 1 of this invention carries out defective conduction. It is a figure explaining the operation | movement when both between the electrode in 1st Embodiment of this invention and a water storage tank, and between a metal flange and a water storage tank conduct poorly. It is a conceptual diagram explaining the structure of the electric water heater in Embodiment 2 of this invention. It is a conceptual diagram explaining the structure of the electric water heater in Embodiment 3 of this invention.

Explanation of symbols

1: Water storage tank 2: Water supply pipe 3: Pressure reducing valve 4: Hot water supply pipe 5: Relief valve 6: Heater (electric heating element)
6A: Nichrome wire (heat generating part)
6B: U-shaped tube (protection part)
6C: Switch 6D: AC power supply 7: Metal flange 8: Packing 9: Housing 10: Electrode 11: Water detection sensor (water detection means)
11A: DC power supply 11B: switch 11C: resistor 11D: resistor 11E: comparator 11F: terminal 11G: terminal 11H: terminal 11J: terminal 11K: resistor 11L: resistor 11M: switch 11N: resistor 11P: switch 12: control circuit

Claims (4)

A water storage tank, and a heat generating portion that converts electric power into heat, and the heat generating portion is electrically insulated to cover the heat generating portion, and is electrically insulated from the water storage tank. An electric heating element attached to the inside of the water storage tank; an electrode electrically insulated from the water storage tank and attached to a position above the electric heating element inside the water storage tank; the electrode and the protection unit; A DC power source that applies a DC voltage so that the potential of the protective part is low, and water exists up to the position of the electrode due to a change in electrical resistance between the electrode and the protective part. An electric water heater comprising water detecting means for detecting water. The electric water heater according to claim 1, further comprising a control circuit for energizing the electric heating body on condition that the water detection means detects the presence of water. 3. The electric water heater according to claim 1, wherein whether or not water is present up to a position of the electrode is checked by the water detection unit at a predetermined period during energization of the electric heating body. The electric water heater according to any one of claims 1 to 3, wherein a portion having a predetermined thickness from a surface of the electrode in contact with water is made of metal having a smaller ionization tendency than hydrogen.

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