JPH0975218A - Electric water heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric water heater which is low in cost and which does not generate much heat in the circuit board and turns off to the safety side at troubles, by providing a rectifying element, a condenser, a switching part, and a Zener diode having a Zener voltage larger than a specified voltage, parallelly connected to the condenser. SOLUTION: A relay contact 16 is connected to a heater 4 of a water heater in series and a surge-absorption element 18 and a condenser 19 are parallelly connected. The switching part 23 is composed of a TRIAC for instance and both ends thereof are connected to the first and the second lead wires 24, 25a respectively. The cathode of a Zener diode 39 is connected to the first lead wire 24 and the anode of the Zener diode 39 is connected to the third lead wire 25b. In this way, the Zener diode 39 are parallelly connected to the condenser 30 and set at a higher voltage than the Zener voltage of the Zener diode 27.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric water heater.

[0002]

2. Description of the Related Art Conventionally, a water heater of this type is disclosed in, for example, Japanese Patent Publication No. 6-85736. According to this publication, a relay and a heater are connected in series to an AC power supply, and a control unit (microcomputer) is connected to the AC power supply via a power supply circuit. A control signal is output from the control unit to the relay in response to the input of the temperature sensor.

[0003]

However, in this water heater, a low-voltage DC voltage with a small voltage fluctuation is required for the control unit, so that the power supply circuit described above requires a transformer, a rectifying circuit, and a smoothing circuit. There is a first drawback that goes high.

Therefore, the means for disposing the metal oxide resistor on the circuit board and stepping down the AC power source has a second drawback that the resistor requires a large space on the circuit board and the amount of heat generated by the resistor is large.

Therefore, the inventor connected a rectifying element and a capacitor to the heater, and connected a switching unit to the capacitor. Then, the switching unit is switched in accordance with the voltage across the capacitor to stabilize the voltage across the capacitor to form a power supply circuit. However, if the switching unit fails in open mode, for example, the voltage across the capacitor exceeds a predetermined voltage, a current exceeding the normal current flows in the power supply circuit, each component heats up, and the circuit board overheats. There are drawbacks.

Therefore, in consideration of such conventional drawbacks, the present invention is an electric water heater which is low in cost, generates a small amount of heat in the circuit board, and becomes inoperative on the safe side when a component in the power supply circuit fails. I will provide a.

[0007]

In order to solve the above-mentioned problems, the present invention switches a rectifying element, a capacitor and a heater connected in series to an AC power source and a voltage so that the voltage across the capacitor is maintained at a substantially predetermined voltage. And a zener diode having a zener voltage higher than a predetermined voltage and connected in parallel with the capacitor.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of an electric water heater according to the present embodiment, and FIG. 2 is an electric circuit diagram of the electric water heater. In these drawings, the frame 1 has a cylindrical shape, and the container 2 has a bottomed cylindrical shape which is installed in the frame 1. The heater set 3 is composed of a water heater 4 and a heater (for keeping heat) 5 that are closely attached to the bottom of the container 2 that stores water and the like. The back cover 6 is fixed to the lower part of the frame 1, and a storage space 7 is provided between the back cover 6 and the bottom wall of the container 2.

The hot water supply pipe 8 has one end communicating with the container 2 and the other end extending out of the frame 1. The hot water supply pump 9 is located in the path of the hot water supply pipe 8, is arranged and fixed in the storage space 7, and is driven by the DC motor 10. The storage box 11 includes a water heater 4, a heater 5, and a hot water supply pump 9.
It contains the control parts for controlling.

The temperature sensor 12 is closely attached to the outer bottom surface of the container 2, the lid 13 is provided on the upper part of the frame 1 so as to be openable and closable, and the passage 13a is a vapor passage in the container 2. The hot water supply switch 14 is provided on the upper part of the front surface of the main body, and the reboil switch 15 is provided on the lower part.

Next, the electric circuit will be described with reference to FIG. The relay contact 16 is connected in series to the water heater 4 and is connected to the AC power supply 17. Surge absorption element 1
8 and the capacitor 19 are connected in parallel, one end of which is connected in parallel is connected to one end 20 of the AC power supply 17, and the other end is connected to the other end 21 of the AC power supply 17.

The surge absorbing element 18 is composed of, for example, a varistor, and when a voltage of about 100 V is applied, it works as a high resistance and has almost no influence on other circuits. However, when a medium-scale surge voltage from an external device is applied, the surge absorbing element 18 acts as a low resistance and absorbs energy due to the surge voltage. The rectifying elements D1, D2, D3, and D4 form, for example, a bridge rectifying circuit 22, and full-wave rectify the AC voltage.

The switching unit 23 is made of, for example, TRIAC, and both ends thereof are connected to the first lead wire 24 and the second lead wire 25a, respectively. Further, the switching unit 23 may be composed of a transistor or the like. The detection circuit 26 is a Zener diode 27 (Zener voltage is, for example, 11V).
And a resistor 28 in series, one end of which is connected to the gate of the switching unit 23 and the other end of which is connected to the third lead wire 25b.

The diode 29 is connected between the second lead wire 25a and the third lead wire 25b, one end of the capacitor 30 is connected to the first lead wire 24, and the other end is connected to the third lead wire 25b. . Thus, the one end 20 of the AC power supply 17, the rectifying elements D1, D2, D3, D4, the capacitor 30, the heater 5, and the other end 21 of the AC power supply 17 are connected in series. Further, the switching unit 23 includes a diode 29
It is connected in parallel to the capacitor 30 via.

In the relay circuit 31, a coil and a diode are connected in parallel, one end of the relay circuit 31 is connected to the collector of the transistor 32, and the other end is connected to the third lead wire 25b.

The emitter of the transistor 32 is connected to the first lead wire 24, the base of the transistor 32 is connected to the midpoint between the resistors 33 and 34, and the other end of the resistor 34 is the first.
The other end of the resistor 33 is connected to the lead wire 24, and is connected to a terminal P1 of a control unit 35 (for example, a microcomputer).

One end of the hot water supply pump 9 composed of the DC motor 10 is connected to the collector of the transistor 36 via the hot water supply switch 14, and the other end of the hot water supply pump 9 is connected to the third lead wire 25b. The emitter of the transistor 36 is connected to the first lead wire 24, and the base of the transistor 36 is connected to the resistors 37 and 3.
8, the other end of the resistor 37 is connected to the first lead wire 24, and the other end of the resistor 38 is connected to the terminal P of the control unit 35.
Connected to 2.

The cathode of the Zener diode 39 is the first
It is connected to the lead wire 24, the anode of the Zener diode 39 is connected to the third lead wire 25b, and thus the Zener diode 39 is connected in parallel to the capacitor 30,
The Zener voltage is, for example, about 15V, which is set higher than the Zener voltage of the Zener diode 27.

The cathode of the Zener diode 40 is the first
It is connected to the lead wire 24 and the anode is the transistor 41.
Of the resistor 42, one end of which is connected to an intermediate point between the Zener diode 40 and the base of the transistor 41, and the other end of which is connected to the third lead wire 25b. The collector of the transistor 41 is connected to the third lead wire 25b, and the emitter is connected to the fourth lead wire 25c.

One end of the capacitor 43 is connected to the first lead wire 24.
The other end is connected to the fourth lead wire 25c. The portion of the ground symbol connected to each terminal of the control unit 35 indicates that it has the same potential as the fourth lead wire 25c.

One end of the fifth lead wire 44 is connected to the first lead wire 2
4 and the other end is connected to the terminals P3 and P4 of the control unit 35. Further, the other end of the fifth lead wire 44 is connected to a terminal P5 through a heat retention lamp 45 and a resistor, and a water heating lamp 46
And a terminal P6 via a resistor, and the reboil switch 15 and a terminal P7 via a resistor.

One end of the temperature sensor 12 has a fifth lead wire 4
4, the other end is connected to the terminal P8 of the controller 35 via the resistor 47, and the other end is connected to the same potential portion as the fourth lead wire 25c via the resistor 48. These components constitute the electric water heater according to the present embodiment.

Next, the operation of this electric water heater will be described again with reference to FIGS. 1 and 2. First put water in container 2,
Insert the power plug of the electric water heater into a power outlet (neither shown).

When the AC power source 17 has a positive potential, the rectifying element D
Current flows through the first and first lead wires 24, the capacitor 30, the third lead wire 25b, the diode 29, the second lead wire 25a, the rectifying element D2, and the heater 5, and the voltage across the capacitor 30 starts to rise. At this time, the switching unit 23 is off because the voltage across the capacitor 30 is still low.

When the voltage across the capacitor 30 becomes equal to or higher than the Zener voltage of the Zener diode 27 (for example, 11V), a current flows through the detection circuit 26, a gate current flows through the switching unit 23, and the switching unit 23 is turned on. Then, from the AC power supply 17, the rectifying element D1, the first lead wire 24, the switching unit 23, and the second lead wire 25a.
A current flows to the rectifying element D2 and the heater 5.

As a result, the voltage across the capacitor 30 drops, current stops flowing to the detection circuit 26, and the switching unit 23 is turned off. When the switching unit 23 is turned off in this way, the capacitor 30 is charged again, and the voltage across the capacitor 30 starts to rise again.

As described above, the switching section 23 performs the switching operation so that it is turned on when the voltage across the capacitor 30 is equal to or higher than the predetermined voltage and turned off when the voltage across the capacitor 30 is lower than the predetermined voltage. That is, the switching unit 23 is the capacitor 3
Switching is performed so that the voltage between both ends of 0 becomes substantially a predetermined voltage (for example, about 11 V).

When the AC power source 17 is at a negative potential, the heater 5, the rectifying element D3, the first electrode 21
A current flows through the lead wire 24, the capacitor 30, the third lead wire 25b, the diode 29, the second lead wire 25a, the rectifying element D4, and the one end 20 of the AC power supply 17. The subsequent operation is the same as in the case of the positive potential described above.

In the power supply circuit 49, since the heater 5 has a relatively low impedance (about 300 ohms), the hot water supply pump 9 as a load circuit and the relay circuit 31.
And the control unit 35 are all connected, each circuit 9, 31, 35
Can supply sufficient current. As described above, the power supply circuit 49
Are load circuits 9 and 3 connected to both ends of the capacitor 30.
1 is supplied with a DC voltage of about 11V. Further, the voltage across the capacitor 30 is stepped down by the Zener diode 40, and a DC voltage of about 5V is supplied to the control unit 35, and thus a stable voltage is supplied.

Since the water temperature in the container 2 is low when the power is turned on, the resistance value of the temperature sensor 12 is large. The voltage corresponding to this large resistance value is applied to the terminal P8 in the control unit 35.
Control unit 35 outputs the “L” signal to the terminal P1. As a result, the lead wire connected to the terminal P1 has a low voltage, the transistor 32 is turned on, and the relay circuit 3
1 is energized and the relay contact 1 connected to the relay circuit 31
6 is turned on, and the water heater 4 is energized. Then, both the heater 4 for heating water and the heater 5 generate heat to perform water heating.

Next, when the temperature of the hot water rises to almost the boiling temperature, the resistance value of the temperature sensor 12 becomes small, and the control unit 3
The output to the terminal P8 of No. 5 becomes a predetermined value, the control unit 35 determines "boiling", and outputs the "H" signal to the terminal P1.
As a result, the voltage of the lead wire connected to the terminal P1 rises, the transistor 32 turns off, the relay circuit 31 turns off, the relay contact 16 turns off, the water heater 4 turns off, and the heat retention operation starts. .

When the user needs hot water and turns on the hot water supply switch 14, the control unit 35 outputs the "L" signal to the terminal P2 when the temperature is kept warm, so that the lead wire connected to the terminal P2 has a low voltage. , The transistor 36 turns on,
The DC motor 10 is energized, the hot water supply pump 9 is energized, and hot water discharge is started.

The rectifying elements D1 to D4 and the capacitor 3
0, the heater 5, or the rectifiers D1 to D4, the switching unit 23, and the circuit of the heater 5 flow current, so that the heater 5 is always energized and consumes substantially constant power (for example, 32 W). As a result, in an electric water heater having a capacity of about 2.2 liters, the heat insulation power is appropriate. This is the end of the description of the normal operation of the electric water heater.

Next, in a power supply circuit 49 consisting of the rectifying elements D1, D2, D3, D4, the switching unit 23, the diode 29, the heater 5, the detection circuit 26 and the capacitor 30, a certain component, for example, the switching unit 23 is used. When a failure occurs in the open mode, no current flows in the switching unit 23.

As a result, the charging current to the capacitor 30 increases, and the voltage across the capacitor 30 exceeds a predetermined voltage (for example, about 11V). When the voltage across both ends becomes larger, a current flows through the Zener diode 39 (the Zener voltage is about 15V) connected in parallel with the capacitor 30. As a result, the Zener diode 39 generates heat that greatly exceeds the allowable thermal loss, and the Zener diode 39 fails in the short-circuit mode within a relatively short time. As a result, the voltage across the capacitor 30 becomes substantially zero V, the voltage supplied to the control unit 35 becomes substantially zero V, and the electric water heater becomes inoperative.

That is, the heat retaining lamp 45 and the water heating lamp 4
6 is de-energized, and the user determines that the electric water heater has failed. Further, the relay circuit 31 is de-energized, and the water heater 4 is also de-energized, so that safety is ensured. In addition, parts in the power supply circuit 49 (rectifier elements D1, D
Since the applied voltage of 2, D3, D4, the capacitor 30, the heater 5 and the like) is substantially zero V, abnormal heat generation does not occur and the circuit board does not overheat. As described above, most of the rectified current flows through the Zener diode 39, but since the voltage across the Zener diode 39 (that is, the voltage across the capacitor 30) is approximately zero V, the Zener diode 39 generates less heat and burns the circuit board. do not do.

[0037]

As described above, according to the present invention, the voltage from the AC power source is rectified by the rectifying element and reduced by the heater,
The voltage across the capacitor rises, and when the voltage across the capacitor exceeds a predetermined voltage, the switching unit turns on and current flows through the switching unit, the charging current of the capacitor disappears, and the voltage across the capacitor drops. In this way, the switching unit repeats switching so as to keep the voltage across the capacitor substantially constant, so that a substantially constant voltage can be supplied to the load circuit connected in parallel with the capacitor.

Further, since the power supply circuit is composed of the rectifying element, the switching section, the heater as the step-down resistor and the capacitor, an expensive power supply transformer as in the conventional case is not required, so that the power supply circuit is inexpensive, compact and has a small voltage fluctuation. can get. In this way, the relay circuit, the hot water supply pump, and the power supply circuit for supplying the voltage to the control unit can be shared, so that the manufacturing can be performed at a lower cost than the conventional product in which the rectifying circuit and the smoothing circuit are individually provided. Further, unlike the conventional case, since it is not necessary to use a large-sized metal oxide resistor, the circuit board generates less heat and a small circuit board is sufficient.

When a component in the power supply circuit, such as the switching unit, fails in the open mode, no current flows in the switching unit and the voltage across the capacitor exceeds a predetermined voltage. Then, a current flows through the Zener diode connected in parallel with the capacitor, and the Zener diode fails in the short circuit mode. As a result, the charging current to the capacitor disappears, the voltage across the capacitor becomes approximately zero V, and it is possible to prevent excessive heat from being applied to the components in the power supply circuit due to excessive voltage. In addition, the voltage supplied to the control unit is substantially zero V, and the electric water heater is in an inoperative state, so that safety can be secured. Since the heat-retaining lamp and the like are de-energized, the user can clearly determine that the electric water heater has failed.

[Brief description of drawings]

FIG. 1 is a sectional view of an electric water heater according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the electric water heater.

[Explanation of symbols]

 D1, D2, D3, D4 Rectifying element 5 Heater 23 Switching part 30 Capacitor 39 Zener diode

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kazuki Asai 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A rectifying element, a capacitor, and a heater that are connected in series to an AC power source, a switching section that switches so as to maintain a voltage across the capacitor at a substantially predetermined voltage, and a Zener voltage that is higher than the predetermined voltage. An electric water heater comprising a Zener diode connected in parallel to the capacitor.