JPH0773062B2 - Sealing lead-acid battery charging method and charging device - Google Patents

Description

The present invention relates to a method for charging a sealed lead acid battery and a charging device.

[Prior Art] Conventionally, as a method of charging a sealed lead-acid battery, a normal charging current is supplied until the charging voltage reaches the terminal charging voltage, and when the charging voltage reaches the terminal charging voltage, the charging current is changed to a minute charging current. A charging method (trickle charging method) for switching to is known. When attempting to charge a sealed lead-acid storage battery (hereinafter referred to as an over-discharge storage battery) after being left over-discharge by this charging method, there is a problem that the battery cannot be sufficiently charged if the internal resistance of the over-discharge storage battery becomes high. This is because when a conventional charging device that performs the above charging method is used to charge an over-discharged storage battery with a high internal resistance, the charging voltage becomes higher than the end-of-charge voltage due to the high internal resistance immediately after the start of charging,
This is because the end-of-charge voltage detector operates and the charging current is switched to the minute charging current.

Therefore, in order to solve such a problem, the applicant first applied a current in the opposite direction to the normal charging for a predetermined period immediately after the start of charging to the over-discharged storage battery until the battery voltage became a negative state. We proposed a method of charging the battery after lowering the internal resistance of the over-discharged storage battery (hereinafter referred to as reverse charging) (Japanese Patent Application No. 61-16196).

[Problems to be Solved by the Invention] When the above charging method is applied to an actual charging device, the problem is how to terminate the reverse charging. In the conventional method previously proposed by the applicant, the reverse charging time is constant (for example, 1 hour). However, as a result of research conducted by the inventor, it has been found that overcharged storage batteries have different reverse charging effects depending on the ambient temperature, resulting in different recoverability of battery performance. This is because even if the internal resistance of the battery is the same, when the ambient temperature of the battery is low, the decrease rate of the internal resistance when performing reverse charging is lower than that when the ambient temperature is high. Therefore, if the reverse charging is uniformly performed for a certain period of time, the internal resistance cannot be reduced even when the reverse charging is performed when the ambient temperature is low, and there is a problem that the over-discharged storage battery cannot be sufficiently charged. . Further, when the ambient temperature is high, reverse charging is performed more than necessary, which hinders shortening of charging time.

Next, a specific example of this will be shown. The battery used was an over-discharged storage battery of 4V-4Ah sealed lead-acid battery with an internal resistance of 300Ω. The charging characteristics when the reverse charging time was 1 hour were shown in Fig. 4 (A), (B). )Pointing out toungue. FIG. 4 (A) shows the charging characteristics when the battery ambient temperature is 25 ° C., and FIG. 4 (B) shows the charging characteristics when the ambient temperature is 0 ° C. In the case of FIG. 4 (A), normal charging is smoothly performed after reverse charging, and 8 hours
After 30 minutes of normal charging, trickle charging is in progress. However, in the case of FIG. 4 (B), the trickle charging was immediately started when the normal charging was started after the reverse charging, and the satisfactory charging was not performed.

From the above description, it is desired that the reverse charge of the over-discharged storage battery be performed in accordance with the ambient temperature of the battery.

An object of the present invention is to provide a charging method that solves the above problems and a charging device suitable for carrying out the method.

[Means for Solving the Problems] The method of the present invention uses a DC power supply that outputs a DC voltage containing an AC voltage component, and detects that the charging voltage has reached the end-of-charging voltage, and changes the charging current to a minute charging current. When charging the sealed lead-acid battery by switching to, the battery is left over-discharged by applying a reverse voltage to the battery until the battery voltage has a reverse polarity, and then performing the normal charging operation and leaving it over-discharged. An object of the present invention is to improve a charging method for a sealed lead-acid battery that performs a normal charging operation without applying a reverse voltage to the storage battery that is not in a state. In the method of the present invention,
When the AC voltage component is detected from the charging voltage and the AC voltage component is larger than the reference value, it is determined that the storage battery is in the over-discharged state, and the reverse voltage is applied to the storage battery even if the charging voltage is the end-of-charge voltage. Apply. Then, using a timer that changes the timer time period in inverse proportion to the change in the ambient temperature of the storage battery and starts counting the timer time period from the start of charging, the reverse voltage is applied to the storage battery until the timer time period counting is completed. To do.

In the specification of the application, "inverse proportion" does not only mean a case of being inversely proportional to a linear function, that is, a linear function, but also includes a case of being inversely proportional to a quadratic function.

Further, in the charging device of the present invention, the DC power supply 1 that outputs the DC voltage including the AC voltage component is used as the charging power supply.
In order to detect the end-of-charge voltage, the end-of-charge voltage detector 4 which detects the end-of-charge voltage of the sealed lead-acid battery B and outputs the end-of-charge voltage detection signal S2 when the end-of-charge voltage exceeds the end-of-charge voltage is provided. An AC voltage component detection that detects an AC voltage component from the charging voltage to detect an overdischarge neglected state and judges that the AC voltage component is overdischarge neglected state and outputs an AC voltage component detection signal S3 A vessel 5 is provided.

When the AC voltage component detection signal S3 is output, the voltage polarity switching circuit 7 that outputs the voltage polarity switching signal S5 and the current value switching stop signal S6 only for a predetermined time, and the end-of-charge voltage detection signal S2.
When the current value switching command signal S1 is input, the current value switching command signal S1 is output, but when the current value switching stop signal S6 is input, the current value switching command signal S1 is not output. Set up. When the current value switching command signal S1 is input, the current value switching circuit 2 that switches the charging current to the minute charging current, and the voltage polarity switching signal S5 is provided between the current value switching circuit 2 and the storage battery B. And a polarity changeover switch circuit (L, SW1, SW2) for applying the charging voltage to the storage battery B in the opposite polarity only during a certain period.

In addition to the above configuration, the present invention is provided with a temperature detecting means for detecting the ambient temperature of the storage battery B, has a timer time period that changes in an inversely proportional relationship to the change in the ambient temperature, and counts the time period after the start of charging. A temperature-corresponding timer circuit 6 that outputs a timer signal until the timer time period is completed is provided, and then a voltage polarity switching circuit 7 is provided for the voltage polarity switching signal during which the temperature-corresponding timer circuit outputs the timer signal S4. It is configured to output S5 and current value switching stop signal S6.

The temperature-corresponding timer circuit 6 uses a temperature-sensitive resistance element having a negative temperature coefficient as an ambient temperature detecting means, and a capacitor charged by a constant DC voltage via the temperature-sensitive resistance element and a charging voltage of the capacitor are It is preferable to use a voltage comparator that outputs a timer signal S4 until it reaches a predetermined reference value.

[Operation] When the ambient temperature of the storage battery is detected and the time for applying the reverse voltage is changed in inverse proportion to the change of the ambient temperature, when the ambient temperature is low and the rate of decrease in internal resistance due to reverse charging of the over-discharged storage battery is small, The reverse charging time becomes long, and the internal resistance can be surely reduced before starting normal charging. When the ambient temperature is high and the reduction rate of the internal resistance due to the reverse charging of the over-discharged storage battery is large, it is possible to prevent the increase of the charging time and the increase of heat generation during the charging by the reverse charging for a relatively short time. Therefore, according to the method of the present invention, so-called trickle charging can be reliably performed within an optimum time.

Further, in the method and apparatus of the present invention, in charging a storage battery by a DC power supply containing an AC voltage component in the output, if the AC voltage component in the charging voltage is detected, the internal resistance of the battery can be detected, and overdischarge Detect the condition. In the device of the present invention, the temperature corresponding to the ambient temperature of the storage battery is detected by the temperature detecting means, and the temperature corresponding timer circuit 6 whose timer time period is changed in inverse proportion to the detected change in the ambient temperature is provided, and the timer time period of the timer circuit 6 is changed. Based on the voltage polarity switching circuit 7
By changing the output time of the signals S5 and S6 output from the current value switching control circuit 3 to the polarity switching switch circuit, the reverse charging time is changed according to the ambient temperature. Therefore, according to the device of the present invention, the reverse charging time can be reliably controlled with a simple configuration according to the change in the ambient temperature.

In addition, the overdischarge battery with low internal resistance that does not require reverse charging,
Quick charging is performed by the normal charging method without performing reverse charging.

Embodiments Embodiments of the method and apparatus of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic circuit diagram of an embodiment of the present invention. In the figure, reference numeral 1 is a DC power supply which transforms the output of the AC power supply AC into a predetermined voltage by a transformer T and performs full-wave rectification by the diodes Da and Db. A current value switching circuit 2 that switches the charging current to a minute charging current when the current value switching signal S1 is input is connected to the positive output terminal of the DC power supply 1. The current value switching circuit 2 inserts an impedance that can supply a normal charging current into the energizing circuit until the signal S1 is input, and when the signal S1 is input, the charging current is a minute charging (trickle charging) current. The charging current value is switched by inserting the impedance for switching to the energizing circuit.

The switches SW1 and SW2 are provided between the current value switching circuit 2 and the sealed lead storage battery B, and are polarity switching switches that apply a charging voltage to the storage battery B with a reverse polarity only while the voltage polarity switching signal S5 is being output. Make up the circuit. These switches
SW1 and SW2 are electromagnetic switches, and when a current flows through the coil L of the electromagnetic relay of the voltage polarity switching circuit 7 described later,
The contact a is switched to the contact b so as to apply a reverse voltage to the storage battery B.

The end-of-charge voltage detector 4 detects the charge voltage of the storage battery B, and outputs the end-of-charge voltage detection signal S2 when the voltage reaches the end-of-charge voltage. The AC voltage component detector 5 detects the AC voltage component of the charging voltage and outputs the AC voltage component detection signal S3 when the voltage component is equal to or higher than the reference value. The detector 5 detects an AC voltage component, that is, a pulsating voltage from the charging voltage for the purpose of detecting the internal resistance of the storage battery B. Then, the above-mentioned reference value to be compared with the detected AC voltage component is the voltage value in charge of the AC voltage component corresponding to the internal resistance that needs to be reverse-charged in advance by examining the relationship between the battery internal resistance and the AC voltage component. Is the standard value.

The temperature-corresponding timer circuit 6 constituting the timer detects the ambient temperature or the environmental temperature of the storage battery B using a temperature detecting means having a negative temperature coefficient such as a thermistor, and the timer time limit is inversely proportional to the change in the detected temperature. And a variable timer circuit capable of changing Then, when the charging of the storage battery B is started, the timer circuit 6 counts the timer time period and outputs the timer signal S4 until the timer time period is completed. Therefore, the timer circuit 6 operates so that the higher the ambient temperature, the shorter the reverse charging time, and the lower the temperature, the longer the reverse charging time.

When both the AC voltage component detection signal S3 and the timer signal S4 are input, the voltage polarity switching circuit 7 switches to the polarity switching circuit (coil L, switches SW1 and SW2) while the timer signal S4 is being input. The voltage polarity switching signal S5 is output and the current value switching stop signal S6 is sent to the current value switching control circuit 3.
Is output.

In principle, the current value switching control circuit 3 receives the current value switching command signal when the detection signal S2 is output from the end-of-charge voltage detector 4.
S1 is output, but when the current value switching stop signal S6 is input, the current value switching command signal S1 is not output even if the detection signal S2 is output from the end-of-charge voltage detector 4. . Therefore, while the reverse voltage is applied to the storage battery B, the charging current is not switched to the minute charging current by the current value switching circuit 2.

Next, the operation when the present invention is carried out using the apparatus shown in FIG. 1 will be described. First, in Fig. 2 (A), the rating is 4V-4A.
Fig. 3 shows the charging characteristics when an overdischarge storage battery with an internal resistance of 300Ω and an ambient temperature of 25 ° C was charged according to the present invention. When the switch SW is closed, the charging voltage is applied to the storage battery B, but when the internal resistance is high, the charging current I hardly flows and the charging voltage V is considerably larger than the end-of-charging voltage Vs. Therefore, the end-of-charge voltage detector 4 immediately outputs the detection signal S2 to the current value switching control circuit 3. The AC voltage component of the charging voltage V at this time has a value considerably larger than the reference value. Therefore, from the AC voltage component detector 5, the AC voltage component detection signal S3
Is output and the signal is input to the voltage polarity switching circuit 7.

On the other hand, the temperature-corresponding timer circuit 6 outputs the timer signal S4 for a time length (1 hour in this example) corresponding to the ambient temperature of the storage battery B of 25 ° C.

The voltage polarity switching circuit 7 outputs the current value switching stop signal while the timer signal S4 is being input, that is, for one hour in this example.
It outputs S6 and the voltage polarity switching signal S5.

The current value switching control circuit 3 receives the detection signal S2 from the end-of-charge voltage detector 4 while the current value switching stop signal S6 is being input.
Even if is output, the current value switching command signal S1 is not output. Therefore, the current value switching circuit 2 is kept as it is in the tempered dance for passing the normal charging current.

A voltage polarity switching signal S5 is sent from the voltage polarity switching circuit 7 to the coil L.
Then, the switches SW1 and SW2 are switched to the contact b side, and a voltage of reverse polarity is applied to the storage battery B. Even when the above switch is switched, the voltage polarity switching circuit 7 is configured to continue to output the signals S5 and S6 while the timer signal S4 is being input.

The temperature corresponding timer circuit 6 stops the output of the timer signal S4 one hour after closing the switch SW. As a result, the output of the signals S5 and S6 from the voltage polarity switching circuit 7 is stopped,
The switches SW1 and SW2 are switched to the contact a side to complete the reverse charging, the charging voltage of the normal polarity is applied to the storage battery B, and the normal charging is performed for about 7 hours and 20 minutes. When the charge voltage V reaches the end-of-charge voltage Vs, the end-of-charge voltage detector 4 outputs a detection signal S2, and the current value switching control circuit 3 receives this signal and sends the current value switching signal S1 to the current value switching circuit. Two
Output to. As a result, the charging current I is switched to the minute charging current, and trickle charging is started.

Next, FIG. 2B shows the same rating as that of FIG.
FIG. 3 shows the charging characteristics when an overdischarge storage battery having the same internal resistance and an ambient temperature of 0 ° C. is charged according to the present invention. In this case as well, the device of FIG. 1 operates in accordance with the above description, except that the temperature-corresponding timer circuit 6 corresponds to the ambient temperature of the storage battery B of 0 ° C. and the temperature of FIG. Longer time than in the case of ℃ (1 hour and 30 minutes in this example)
The timer signal S4 of is output. Thereby, the reverse charge of the storage battery B is performed for 1 hour and 30 minutes. That is, as compared with the case of FIG. 2 (A), the normal charging is started after the reverse charging for a long time, the charging voltage V reaches the terminal charging voltage Vs after the smooth normal charging for about 8 hours, and the charging current I becomes small. Switching to charging current, trickle charging is in progress.

As described above, when the battery ambient temperature is low, by increasing the reverse charging time compared to when the temperature is high, normal charging is smoothly performed after sufficiently reducing the internal resistance,
Satisfactory recovery of battery performance is obtained.

The above describes the case of an over-discharged storage battery with a high internal resistance, but in the case of an over-discharged storage battery with a low internal resistance, the charging voltage is below the end-of-charge voltage and the AC voltage component of the charging voltage is also small. Therefore, detection signals are not output from the end-of-charge voltage detector 4 and the AC voltage component detector 5, and normal charging is performed without reverse charging.

(Specific Example) FIG. 3 shows a specific circuit configuration of the embodiment of FIG. In the figure, the same parts as those in the configuration of FIG. 1 are designated by the same reference numerals as those shown in FIG. The current value switching circuit 2 is composed of resistors R1 and R2 and transistors Tr1 and Tr2. The resistance value is R1
> R2. When the transistor Tr1 is conducting, the resistor R2 and the resistor R1 are inserted in parallel into the charging circuit to allow a large charging current to flow, and when the transistor Tr1 is cut off, a minute charging current flows through the resistor R1. When the transistor Tr1 becomes conductive, the light emitting diode LED described below emits light to display the charging state.

The current value switching control circuit 3 is composed of transistors Tr3, Tr4 and Tr5, resistors R3 to R6, a light emitting diode LED, etc., and when neither the end-of-charge voltage detection signal S2 nor the current value switching stop signal S6 is input, the resistor R7 Through transistor Tr
When the base current is supplied to 3 and the transistor Tr3 becomes conductive, a conduction signal is given to the transistor Tr1 of the current value switching circuit 2.

The end-of-charge voltage detector 4 is composed of a Zener diode ZD1, a thyristor SCR1, resistors R7 to R9, a capacitor C2, etc., and a charging voltage is applied to the Zener diode ZD1 while the switches SW1 and SW2 are in contact with the contact a. Is applied. When the charging voltage is equal to or higher than the end-of-charging voltage and the charging voltage exceeds the Zener voltage of the Zener diode ZD1, the Zener diode ZD1 becomes conductive and the firing signal is supplied to the gate of the thyristor SCR1. As a result, the thyristor SCR1 becomes conductive and the transistor Tr3 is cut off. If at this time
When the internal resistance of the battery B is low, the AC voltage component detector 5 does not output the AC voltage component detection signal S3, and the voltage polarity switching circuit 7 does not output the current value switching stop signal S6, the transistor Tr4 is Since the transistor Tr3 is in the non-conducting state, the transistor Tr3 of the switching circuit 2 is turned off by the interruption of the transistor Tr3 to switch to the charging of the minute charging current.

When the internal resistance of the battery B is large, the AC voltage component detector 5 outputs the AC voltage component detection signal S3 and the voltage polarity switching circuit 7 outputs the current value switching stop signal S6, so that the transistor Tr4 is in the conductive state. Therefore, even if the transistor Tr3 is cut off, the cutoff of the transistor Tr1 is blocked.

The AC voltage component detector 5 is composed of operational amplifiers OP2, OP3, a diode D4, capacitors C5 to C7, resistors R23 to R30, and the like.

Then, the DC component is subtracted from the charging voltage by the capacitor C5 and the resistor R23, and only the AC voltage component is input. The AC voltage component amplified to a predetermined value through the operational amplifier OP2 charges the capacitor C6, the terminal voltage of the capacitor C6 is input to the + input terminal of the operational amplifier OP3 that constitutes the comparator, and the resistor R11 and the variable resistor VR1 are used. First composed
Is compared with the reference voltage output from the reference voltage setting device. This reference voltage is a voltage value corresponding to an AC voltage component corresponding to the internal resistance that needs to be reverse-charged by previously examining the relationship between the internal resistance of the storage battery and the AC voltage component. Therefore, when the internal resistance of the battery is high enough to require reverse charging, the operational amplifier OP3 outputs the detection signal S3.

The voltage polarity switching circuit 7 includes transistors Tr6 to Tr8, thyristor SCR2, diode D2, resistors R16 to R22, and capacitor C.
4 and the coil L of the relay. Then, when the AC voltage component detection signal S3 is output, the thyristor SCR2 becomes conductive, as a result, the transistors Tr7 and Tr6 become conductive, and the transistor Tr8 becomes conductive, so that an exciting current is supplied to the coil L and the switch is turned on. SW1
And SW2 are switched from the a-contact to the b-contact, and the reverse voltage is applied to the battery B.

The temperature compatible timer circuit 6 includes a temperature sensitive resistance element R13, a capacitor C3, an operational amplifier OP1, a Zener diode ZD2, and a resistance R1.
0, R12 to R15, a variable resistor VR2 and the like. The temperature-sensitive resistance element R13 is a resistance element in which the internal resistance changes with a negative characteristic in response to the ambient temperature of the storage battery B.
The temperature-sensitive resistance element R13 and the capacitor C3 form a temperature-corresponding time constant circuit, and the terminal voltage of the capacitor C3 is calculated from the reference voltage set by the second reference voltage setting device including the resistor R12 and the variable resistor VR2. When becomes larger, the output (timer signal S4) is not output from the operational amplifier OP1. The time when the operational amplifier OP1 stops the output is the time when the reverse charging is stopped. Until then, the output (signal S4) is output from the operational amplifier OP1, and when the transistor Tr7 is turned on, the transistor Tr6 is also turned on immediately. When the AC voltage component detector 5 outputs the signal S3 and the thyristor SCR2 becomes conductive, the transistor Tr7 becomes conductive, the transistor Tr6 becomes conductive, and as a result, the transistor TR8 becomes conductive. And operational amplifier O
When the output from P1 is stopped, the transistor TR8 is cut off and the switches SW1 and SW2 are switched to the contact a side.

When the thyristor SCR2 is turned on and the transistors Tr7 and Tr6 are turned on, the transistor Tr7 is turned on through the resistors R4 and R6.
A conduction signal (current value switching stop signal S6) is given to 4 and Tr5, and these transistors are turned on. Transistor
The Tr5 has a function of short-circuiting the anode and cathode of the thyristor SCR1 to shut off the thyristor SCR1 during the reverse charging period. This is because if the thyristor SCR1 is conducting when the reverse charge is returned to the normal charge, trickle charge due to a minute charge current is entered, and this is prevented. When the temperature-corresponding time constant circuit (R13, C3) completes counting the time limit and the output of the operational amplifier OP1 disappears, the transistors Tr4, Tr5, and Tr8 are shut off, and normal charging is resumed.

Although the switches SW1 and SW2 are electromagnetic switches in the above embodiment, semiconductor switch circuits may be used as these switches.

[Effect of the Invention] According to the present invention, after detecting the AC voltage component in the charging voltage to determine whether or not the storage battery is in the over-discharged state, the reverse voltage is applied only to the storage battery in the over-discharged state. Therefore, there is no fear that an unnecessary reverse voltage is applied to the storage battery that is not in the overdischarge left state. Also, since the time to detect the ambient temperature of the storage battery and apply the reverse voltage is changed in inverse proportion to the change in the ambient temperature, it is reversed when the ambient temperature is low and the rate of decrease in internal resistance due to reverse charging of the over-discharged storage battery is small. The charging time can be lengthened to reliably reduce the internal resistance before starting normal charging. Also, when the ambient temperature is high and the rate of decrease in internal resistance due to reverse charging of an over-discharged storage battery is large,
By the reverse charging for a relatively short time, it is possible to prevent an increase in charging time and an increase in heat generation during charging. Therefore, according to the method of the present invention, so-called trickle charging can be reliably performed within an optimum time.

Further, according to the device of the present invention, the ambient temperature of the storage battery is detected by the temperature detecting means, and a temperature-compatible timer circuit whose timer time period is changed in inverse proportion to the detected change of the ambient temperature is provided, and the timer time period of the timer circuit is set. Based on the above, by making the output time of the signal output from the voltage polarity switching circuit to the current value switching control circuit and the polarity switching switch circuit variable, the reverse charging time can be varied according to the ambient temperature. It is possible to reliably control the reverse charging time with a simple configuration according to changes in the ambient temperature.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 (A) is a curve diagram showing charging characteristics when an overdischarge storage battery having a high ambient temperature is charged in the embodiment of FIG. 1, and FIG. FIG. 3B is a curve diagram showing the charging characteristics when an overdischarge storage battery with a low ambient temperature is charged in the embodiment of FIG. 1, and FIG. 3 is a specific circuit diagram of the embodiment of FIG. Figures 4 (A) and (B) show 1 for all over-discharged storage batteries with different ambient temperatures.
It is a curve figure which shows the example from which a charge characteristic when reverse charging of time differs is performed. 1 ... DC power supply, 2 ... Current value switching circuit, 3 ... Current value switching control circuit, 4 ... End-of-charge voltage detector, 5 ... AC voltage component detector, 6 ... Temperature-compatible timer circuit, 7 ...... Voltage polarity switching circuit, SW1, SW2 ...... Polarity switching switch circuit,
B: Sealed lead acid battery.

Claims (3)

[Claims] 1. A direct current power supply for outputting a direct current voltage containing an alternating current voltage component is used, and when it is detected that the charging voltage has reached the terminal voltage of charging, the charging current is switched to a minute charging current to charge the sealed lead acid battery. When performing, a normal charging operation is performed on the storage battery in the overdischarge left state until a reverse voltage is applied to the storage battery, and then a normal charging operation is performed. In a method for charging a sealed lead storage battery that performs a normal charging operation without applying a reverse voltage to the storage battery, the storage battery detects the AC voltage component from the charging voltage and the AC voltage component is larger than a reference value. Even if the charging voltage is determined to be in an overdischarge neglected state, the reverse voltage is applied to the storage battery even if the charging voltage is at the end-of-charge voltage, and the relationship is inversely proportional to the change in the ambient temperature of the storage battery. A sealed lead, characterized in that the timer is used to change the timer period and to start counting the timer period from the start of charging, and the reverse voltage is applied to the storage battery until the counting of the timer period of the timer is completed. How to charge a storage battery. 2. A DC power source (1) which outputs a DC voltage containing an AC voltage component, and a charging voltage of a sealed lead storage battery (B) is detected, and when the charging voltage exceeds a charging end voltage, a charging end voltage is detected. Detection signal (S2)
An end-of-charge voltage detector (4) for outputting an AC voltage component detection signal (S3) when an AC voltage component is detected from the charging voltage and the AC voltage component is larger than a reference value.
And an AC voltage component detector (5) for outputting the voltage polarity switching signal (S5) and a current value switching stop signal (S6) when the AC voltage component detection signal (S3) is output. When the circuit (7) and the end-of-charge voltage detection signal (S2) are input, a current value switching command signal (S1) is output, but when the current value switching stop signal (S6) is input, the current A current value switching control circuit (3) configured not to output the value switching command signal (S1), and a current value switching that switches the charging current to a minute charging current when the current value switching command signal (S1) is input. A circuit (2) is provided between the current value switching circuit (2) and the storage battery (B), and the charging voltage is reversed in polarity while the voltage polarity switching signal (S5) is being output. Polarity changeover switch circuit (L, SW1, SW2) applied to the storage battery (B) ) And a temperature detecting means for detecting the ambient temperature of the storage battery (B), and having a timer time period that changes in an inversely proportional relationship to the change in the ambient temperature and starting counting after the start of charging. A temperature-corresponding timer circuit (6) that outputs a timer signal until the timer time period is completed, and the voltage-polarity switching circuit (7) causes the temperature-corresponding timer circuit to output the timer signal (S4). A battery charger for a sealed lead storage battery, which outputs the voltage polarity switching signal (S5) and the current value switching stop signal (S6) for a period. 3. A temperature-corresponding timer circuit (6) uses a temperature-sensitive resistance element having a negative temperature coefficient as the ambient temperature detecting means, and a capacitor charged by a constant DC voltage through the temperature-sensitive resistance element. And a voltage comparator that outputs the timer signal (S4) until the charging voltage of the capacitor reaches a predetermined reference value.