JPH05336677A - Battery charger - Google Patents

Abstract

PURPOSE:To cut the charging time as short as possible without exerting stress on a battery by lowering the charging current when the battery voltage exceeds a set level in the initial charging stage. CONSTITUTION:Upon connection of a battery set 2, a microcomputor 50 turns an analog switch 67b of a charging current control means 60 ON based on a signal delivered from an output port 50 to bring the amplification factor of an operational amplifier 61 at an intermediate level thus producing a charging current I2 of intermediate level. At the same time, output signal from a battery voltage detecting means 40 is subjected to A/D conversion through an A/D converter 55 and taken in as a battery voltage value Vin1 which is then compared with a comparison voltage value Vref1. If Vin1>Vref1, only an analog switch 67a is turned ON to lower the charging current down to I3 whereas when Vin1-Vref1, analog switches 67a, 67b are turned OFF to elevate the charging current upto I3. This circuitry realizes positive decision of the state of gas consuming reaction rate of battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger for charging a secondary battery such as a nickel-cadmium battery (hereinafter referred to as a nicad battery).

[0002]

2. Description of the Related Art Generally, when a charging current is increased in order to charge a secondary battery such as a nickel-cadmium battery in a short time, the gas consumption reaction rate at the cathode decreases as the temperature becomes lower.
It is necessary to reduce the charging current at low temperatures. Then, the applicant has proposed a charging method in which the battery temperature is detected and the charging current is reduced if the battery temperature is equal to or lower than a set value, as in Japanese Patent Application No. 2-187664.

[0003]

However, not only when the battery temperature is low, but the gas consumption reaction rate of the battery decreases, the charging current is large and the amount of electricity remaining in the battery before charging is small. Sometimes it happens. Therefore, when trying to determine the charging current by simply detecting the battery temperature, it is necessary to give a margin to the set battery temperature, and there is a problem in performing efficient short-time charging for a wide range of battery temperatures. Become. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to determine whether or not the gas consumption rate is reduced so that charging can be performed with an appropriate charging current.

[0004]

Therefore, as shown in the charging curve 1b of FIG. 3, when the gas consumption reaction rate of the battery decreases as the temperature decreases, the internal resistance of the battery increases and the charging curve 1a is compared with the normal charging curve 1a. Then, paying attention to the fact that the battery voltage rises, it is determined that the charging voltage exceeds the comparison voltage at the initial stage of charging, and the charging current is reduced.

[0005]

As a result, the state of the gas consumption reaction rate of the battery can be reliably discriminated, so that the charging time can be minimized for a wide range of battery temperatures and the battery can be charged without stress at low temperatures. Extends the life of.

[0006]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Reference numeral 1 is an AC power source, 2 is a battery group to which a plurality of rechargeable batteries are connected, 3 is current detecting means for detecting a charging current flowing in the battery group 2, 4 and 5 are signal transmitting means including photocouplers, 10 Is a full-wave rectifier circuit 11 and a smoothing capacitor 1
A rectifying / smoothing circuit consisting of 2, a high-frequency transformer 21,
It is a charge control unit including a MOSFET 22 and a PWM control IC 23. The charge control means 20 is a single chip microcomputer (hereinafter referred to as a microcomputer) 5 which will be described later.
A signal from the output port 56 of 0 controls the start / stop of charging of the battery set 2. The PWM control IC 23 is a MOS
It is a switching power supply IC that adjusts the output voltage of the rectifying and smoothing circuit 10 by changing the drive pulse width of the FET 22. Three
Reference numeral 0 is a rectifying / smoothing circuit composed of diodes 31, 32, choke coil 33 and smoothing capacitor 34, and 40 is a battery voltage detecting means composed of resistors 41, 42 for detecting the battery voltage of the battery set 2. As is well known, the microcomputer 50 includes a CPU 51, a ROM 52, a RAM 53, a timer 54,
It is composed of an A / D converter 55, an output port 56, a reset input 57 and the like. The microcomputer 50 compares the battery voltage input from the battery voltage detection means 40 with a predetermined comparison reference voltage value in order to determine the state of gas consumption reaction speed of the battery, and based on the comparison result, charging current control means described later. 6
Send a signal to 0 to control the charging current. Also, start charging
A stop signal is generated via output port 56. 60 is an operational amplifier 61, 62, resistors 63a, 63b, 63c,
A charging current control unit composed of 64-66 and analog switches 67a and 67b.
67b is composed of, for example, a CMOSIC 4066 or the like. To reduce the charging current, the amplification degree by the operational amplifier 61 may be increased. That is, in order to maximize the charging current, the analog switches 67a and 67b are turned off to minimize the amplification degree of the operational amplifier 61. To reduce the charging current, only the analog switch 67b is turned on by the signal from the output port 56 of the microcomputer 50 and the amplification degree by the operational amplifier 61 is increased. To further reduce the charging current, only the analog switch 67a is turned on by the signal from the output port 56 of the microcomputer 50, and the amplification degree by the operational amplifier 61 is further increased. 70 is a power transformer 71, a full-wave rectifier circuit 72, a smoothing capacitor 73, a three-terminal voltage regulator 7
4. A constant voltage power supply including a reset IC 75, which serves as a power supply for the microcomputer 50, operational amplifiers 61 and 62, and the like. The reset IC 75 outputs a reset signal to the reset input 57 to initialize the microcomputer 50.

The operation will be described with reference to the circuit diagram of FIG. 1 and the flowchart of FIG. When the power is turned on, the microcomputer 50 enters a standby state for connecting the battery group 2 (step 10
1). When the battery set 2 is connected, the microcomputer 50 determines the battery connection by the output signal of the battery voltage detection means 40, turns on only the analog switch 67b of the charging current control means 60 to set the medium amplification degree, and the charging current is set to the middle level. At the same time as setting the position I ₂ , P from the output port 56 via the signal transmission means 4
A charge start signal is transmitted to the WM control IC 23 to start charging (step 102). Battery set 2 at the same time when charging starts
The charging current flowing through the current detecting means 3 is detected by the current detecting means 3, and the difference between this charging current value and the reference value Vref is detected by the differential amplifying means 60.
The feedback is applied to the PWM control IC 23 via the signal transmission means 5. That is, when the charging current is large, the pulse width is narrowed, and in the opposite case, the pulse width is widened, and a pulse proportional to the pulse width is applied to the high frequency transformer 21, and the rectifying and smoothing circuit 3
At 0, it is smoothed to direct current and the charging current is kept constant. That is, the charging current is controlled to be a constant current via the current detection unit 3, the charging current control unit 60, the signal transmission unit 5, the charging control unit 20, and the rectifying / smoothing circuit 30. The output signal of the battery voltage detecting means 40 which has detected the voltage of the battery set 2 is A / D converted by the A / D converter 55 and taken in as a battery voltage value V _in1 (step 103). In order to determine whether or not the gas consumption reaction speed of the battery has decreased, the input battery voltage value V _in1 is compared with the comparison voltage value V _ref1 (step 104). Analog switch 67 when V _in1 > V _ref1
Only a is turned on to reduce the charging current to I ₃ (step 1
05, see FIG. 4). When V _in1 <V _ref1 , the analog switches 67a and 67b are turned off to increase the charging current to I ₁ (step 106, see FIG. 6). Next, the output signal of the battery voltage detecting means 40 is A / D converted by the A / D converter 55 and taken in as the battery voltage value V _in2 (step 10).
7). The input battery voltage value V _in2 is compared with the comparison voltage value V _ref2 in order to determine whether or not the gas consumption reaction rate of the battery has decreased due to the increase in the charging current (step 108). When V _inn2 > V _ref2 , analog switch 67
Only b is turned on to reduce the charging current to I ₂ (step 109, see FIG. 5). When V _in2 <V _ref2 , the charge current is kept at I ₁ and full charge is determined (step 11).
0). When it is determined that the battery is fully charged, the microcomputer 50 outputs a charge stop signal from the output port 56 via the signal transmission means 4 to PW.
It is transmitted to the M control IC 23 and the charging is stopped (step 1
11). Next, it is determined that the battery group 2 is taken out (step 112). When it is determined that the battery group 2 is taken out, the process returns to step 101 and stands by for charging the next battery group 2.

[0008]

According to the present invention, when the gas consumption reaction rate of the battery decreases as the temperature decreases, the internal voltage of the battery increases and the battery voltage rises. It was determined that the voltage was exceeded and the charging current was reduced. As a result, the state of the gas consumption reaction rate of the battery can be surely determined, so that the charging time of the battery can be minimized for a wide range of battery temperatures. Further, since the battery can be charged at low temperature without applying stress, the battery life is extended.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a charging device of the present invention.

FIG. 2 is a flowchart showing an embodiment of a control method of the charging device of the present invention.

FIG. 3 is a graph showing charge curves at normal temperature and low temperature.

FIG. 4 is a graph showing the relationship between battery temperature, battery voltage and charging current.

FIG. 5 is a graph showing the relationship between battery temperature, battery voltage and charging current.

FIG. 6 is a graph showing the relationship between battery temperature, battery voltage and charging current.

[Explanation of symbols]

Reference numeral 20 is a charge control means, 40 is a battery voltage detection means, 50 is a microcomputer, and 60 is a charge current control means.

Claims (1)

[Claims] 1. A charging control means for controlling charging of a secondary battery, a battery voltage detecting means for detecting a battery voltage during charging, and a comparing means for comparing a battery voltage from the battery voltage detecting means with a set value. And a charging current control means for decreasing the charging current when the comparison means determines that the battery voltage at the initial stage of charging is higher than a set value.