JPH03200082A - How to detect the remaining capacity of a lead-acid battery - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for accurately and quickly detecting the remaining capacity of a lead-acid battery while in use.

Conventional technology] In order to prevent problems caused by the sudden battery discharge of lead-acid batteries, the remaining capacity detection methods of lead-acid batteries conventionally used include electrolyte specific gravity, terminal voltage during large current discharge, or internal resistance. There is a way to estimate it from measurements such as

[Problem that the invention seeks to solve]

Among these methods, the method of measuring the electrolyte specific gravity is complicated to operate, and requires modification of the battery itself, such as incorporating a float that serves as a specific gravity sensor or an electrode (Japanese Patent Application Laid-Open No. 1982-29635) that captures specific gravity using an electrical signal. In addition to being necessary, it is susceptible to the temperature of the electrolyte and maintenance (water replenishment, fluid replacement) conditions, and has disadvantages such as poor correspondence with the remaining capacity at the time of large current discharge, which is an indicator of starting performance.

In the method of measuring terminal voltage during short-time discharge of large current (Japanese Patent Application No. 78029/1989), the relationship between discharge capacity and terminal voltage cannot be obtained unless the measured current is limited to a specific value. , battery forklift batteries, or SLI (Starting.

It is very difficult to know the remaining capacity from the voltage-current information during use in application fields where the discharge current is not fixed, such as in lighting, ignition (lighting, ignition) batteries.

In addition, in the method of measuring internal resistance, the voltage of a lead-acid battery is
Since the relationship between currents is not a linear relationship, a constant DC resistance cannot be specified, and the method using AC resistance (M, Hughes et al.
al, Journal of Applied El
electro-chemistry 16,555 (19
86)) is used, but AC resistance is difficult to measure when using batteries and has the drawback of requiring a separate device for measurement.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and provide a method for accurately and quickly detecting the remaining capacity of a lead-acid battery in its used state, without making any special modifications to the battery itself. shall be.

[Description of the first invention] The present invention measures the temperature of a lead-acid battery, calculates a reference voltage from the voltage-current relationship during large current discharge of the lead-acid battery, and calculates a reference voltage between the reference voltage and the battery. Based on the temperature, a temperature compensation reference voltage at the battery temperature is calculated from a predetermined reference voltage and the relationship between the battery temperature and the temperature compensation reference voltage, and the relationship between the predetermined temperature compensation reference voltage and the remaining capacity is calculated. The present invention relates to a method for detecting the remaining capacity of a lead-acid battery to determine the remaining capacity.

The remaining capacity detection method of the present invention measures the discharge current and terminal voltage at startup as well as the temperature of the electrolyte while the battery is in use. The remaining capacity of the battery can be determined accurately and quickly from the relationship between the temperature compensated reference voltage and the remaining capacity.

The present invention will be described in detail.

The relationship between the discharge current density 1 and the terminal voltage V of a lead-acid battery can be divided into two parts depending on the discharge current density, as shown in FIG. In the small current range, ■ decreases exponentially as ■ increases. In other words, the V-I relationship in the small current range occurs because the discharge reaction resistance is controlled by the activation overvoltage, and unless the contribution of this activation overvoltage is removed, the V-I relationship becomes constant and independent of the current. It is not possible to find the internal resistance of However, the discharge current density in the large current range is 100 mA/cnr to 400 mA/cnr per unit area of the electrode.
In the range of mA/ctJ, the relationship of V-1 has a linear relationship of a linear function. The VI relationship can be found for one battery with a remaining capacity at a certain temperature.

Therefore, we prepared a large number of batteries with different residual capacities at each temperature of 0°0125°C and 50°C, measured the voltage and current at two or more points during large current discharge for each battery, and calculated the V-I line for each battery. I = obtained by linear extrapolation from the slope R (differential internal resistance) of the straight line and the relationship between V-I
The voltage value V0 (pseudo electromotive force) at O was determined. When R and Vo determined from batteries having various residual capacities at each temperature were plotted with symbols assigned to each residual capacity at each temperature, the relationships shown in FIGS. 3 to 5 were obtained.

A battery with a large remaining capacity is located at the upper left in the figure, that is, exhibits low differential internal resistance and high pseudo-electromotive force. ), those with low remaining capacity are located on the right or lower side of the figure, or on the lower right side.

(In other words, it indicates a high differential internal resistance or a low pseudo-electromotive force, or both.) Therefore, if the differential internal resistance and pseudo-electromotive force of an arbitrary battery whose battery temperature is any of the above temperatures are known, FIG. According to the relationship 4.5, the remaining capacity of the battery can be detected by checking where the battery is located in the diagram.

Based on these relationships, the present inventors have established a method for determining the remaining capacity of a lead-acid battery at any temperature and remaining capacity. The remaining capacity and pseudo electromotive force V of the electrolyte of the battery at a temperature of 0°C. In FIG. 3, which shows the relationship between R and the differential internal resistance R, a straight line with a constant slope (this is taken as the reference current I3) passing through each data point is drawn, and the value v3 at the intersection of the straight line and the vertical axis is The slope (3) is determined so that each value has a sufficiently distinguishable difference. That is, L (96) is determined so that V3 and remaining capacity have an optimal correlation as shown in FIG. If V5 of an arbitrary battery at 0° C. is determined from this correlation, the remaining capacity can be determined. The value of V3 is the V- of any battery.
13 can be found from the relationship of I. Figure 3 is for the case of 0°C, and the same can be obtained for the cases of 25°C and 150°C, and I3 is 78.60, respectively.The relationship between V3 and remaining capacity is shown in Figure 4.5. That's right.

The relationship between these 13 and VS and the remaining capacity is when the temperature of the electrolyte of the battery to be measured is 0°C, 25°C, and 150'C. In an actual battery, the temperature of the electrolyte rarely matches the above temperature, and the value of 3 above and the relationship between V5 and the remaining capacity can hardly be used. Therefore, an investigation was conducted to determine the relationship between 13, V3 and the remaining capacity at a given battery temperature.

As mentioned above, the temperature of the electrolyte is 0°C, 125°C, and 50°C.
In the case of C, ■5 was 96.78.60, respectively. Plotting these 15 values for each temperature and finding a linear relationship, Is = Io + aT (r. = 96, a = -0, 7
2) is found. The reference current (3) at any temperature can be determined from this relational expression.

Further, the relationship between the reference voltage (3) and the remaining capacity is also at each electrolyte temperature. Therefore, a study was conducted to find a unified relational expression (V, +bT, which is assumed to be the temperature-corrected reference voltage V8) that holds true at any temperature by introducing a term bT that is a linear function of temperature. In Figures 3 to 5, the inventors determined b (-0,0174) L so that the relationship between V3 and remaining capacity at 25°C and 50°C coincided with the relationship between V3 and remaining capacity in Figure 3 at 0°C. , v, = v, -o, which is independent of temperature. The formula 0174T was obtained.

The thus obtained V and the remaining capacity had a good correlation as shown in FIG. Therefore, for a lead-acid battery of any remaining capacity at any temperature, V
2, the remaining capacity can be determined from the relationship shown in FIG.

The lead-acid battery used in the method for detecting the remaining capacity of a lead-acid battery of the present invention is a battery whose remaining capacity is known in advance at the measurement temperature by a known remaining capacity measuring method. In addition, the discharge current of 100 to 400 mA/crl at startup to determine the voltage-current relationship of any battery varies depending on the battery, but in the case of a 34B'19 battery, it is 10 mA/crl.
8-432A, 192-76 for 55D23 batteries
This corresponds to a discharge at 8 A, which approximately corresponds to the range of pulsating current at engine startup when these batteries are used as SLI batteries. Therefore, in these cases, discharging at several discharge currents can be carried out while the battery remains connected to the circuit.

Also, known methods and devices can be used to determine the temperature of the electrolytic solution and the battery current and voltage.

The remaining capacity in the present invention was expressed as the capacity when the battery was discharged at 20OA. The remaining capacity of a battery changes depending on the magnitude of the discharged current, and the larger the discharge current, the smaller the amount of electricity that can be taken out, that is, the remaining capacity tends to decrease. However, the way in which it decreases is not necessarily constant depending on the battery and its condition, and the discharge capacity in high current discharge cannot be known from the remaining capacity in low current discharge.

Trouble when a galena-acid battery runs out of battery appears in the form of an inability to start the engine, so it is important to know the remaining capacity at a large current discharge equivalent to the starting current. Low current discharge capacities such as hour rate or 20 hour rate capacities were used. For this reason, the remaining capacity of batteries up to now has not necessarily been
It did not correspond to the starting performance of acid batteries. Therefore, the discharge capacity at 200 A, which corresponds to the starting current, was used as the remaining capacity in the present invention.

(Function) In the present invention, it has been found that the reference voltage shows a good correlation with the remaining capacity of the battery. The reason for this is considered as follows. A battery whose remaining capacity has decreased due to deterioration or progress in discharge exhibits phenomena such as an increase in discharge reaction resistance or a decrease in electromotive force. The increase in discharge reaction resistance is due to a decrease in the area of the active material or a break in the lattice metal, and is considered to be obtained by removing the contribution of the activation overvoltage from the DC internal resistance.
It matches the slope of the straight line part of the voltage characteristics. Further, the electromotive force of the battery is considered to be the sum of the V slice of the linear portion of the current/voltage characteristics plus the contribution of the activation overvoltage determined by the temperature. From this, it is natural that there is a strong correlation between current/voltage characteristics and remaining capacity. but,
The reason why the correlation between only one of these intercepts or slopes and the remaining capacity is not necessarily good is because the way batteries deteriorate and how they are charged varies, and even if the batteries have the same remaining capacity, some have differential internal resistance. This is because the symptoms appear in the form of an increase in electromotive force and, in some cases, a decrease in electromotive force. However, if the reference current (3) for determining the reference voltage V3 corresponding to the remaining capacity is appropriately set, the effects of both can be combined, and it is considered that it becomes an index that fits well with the battery characteristics of the remaining capacity.

(Effects) The method for detecting the remaining capacity of a lead-acid battery according to the present invention can detect the temperature of the electrolyte, the discharge current at startup, and the like while the battery is connected to the electric circuit.
By simply measuring the terminal voltage, the remaining capacity of any battery can be determined accurately and quickly from a pre-memorized relationship.

(Description of the Second Invention) The second invention relates to the relationship between the current and the voltage during the pulsating large current discharge at the time of starting. ), (I2, V2)... (1
,,V,) by the least squares method, the most probable linear relationship between the current ■ and the voltage V V=V, -R*I
(Vo [pseudo electromotive force] and R (differential internal resistance)).

As mentioned above, the relationship between current and voltage can be approximated by a straight line in the range of 100 to 400 mA/cnr per unit area of the electrode, and the straight line has a slope R and an intercept V. It can be determined uniquely by To find both of these values for any battery, the relationship between V and I when discharged at a large current for a short time is 2.
Points or more are required.

It is desirable that this number of points be as large as possible in order to improve accuracy. Fortunately, in the case of a lead-acid battery, such a large current discharge that can obtain as many points as possible is achieved at the time of engine startup.

When starting the engine, current flows through the starter motor at the same time as the switch is turned on, but it is known that the current flowing through the motor pulsates as shown in Figure 2 due to the back electromotive force generated by the rotation of the motor. There is. Because the discharge current pulsates in this way, if the battery voltage and battery current at this time are stored at two or more points, the V-1 straight line can be drawn using those points. If there are only two memorized points, the V-■ straight line will be a straight line connecting those two points, but if there are three or more memorized points,
Since not all points are necessarily exactly on a straight line, this is the most likely straight line that passes through those points. The most probable straight line can be found using the method of least squares with high accuracy and is easy to express mathematically. That is, during the pulsating large current discharge at the time of starting, 2 or more n sets of current and voltage sets (1
1, V,), (I2, V2)... (I., V,)
From this, the formula V = VO- expressing the linear relationship between current I and voltage V
V of R*I. (intercept: pseudo electromotive force) and R (slope: differential internal resistance) are determined by the following equations.

Va = (nΣI, ΣI, V, -Σ■,'ΣV,)/
′((ΣII)2 nΣI,′) R= (nΣIk Vh−Σ■,ΣV,)/((ΣIh
)2 nΣ■,') Here, Σ represents the sum of k=1 to n.

V obtained in this way. From and R, V5 is: ■5=V,
-R1.

(Example) In order to demonstrate the effectiveness of the battery state detection method for lead-acid batteries of the present invention, a test battery (NS40ZA type) with unknown remaining capacity was used.
A plurality of batteries were prepared, and an engine starting experiment was conducted using each battery using a car equipped with the system shown in Figure 7.

The device for detecting the remaining capacity shown in FIG. 7 has the following configuration. A test battery 1, a power relay 4 provided between its positive terminal 2 and the starter motor 3, an ammeter 5 and a voltmeter 6 for measuring the current ■ and voltage V during the large current discharge flowing through the starter motor, and the battery A temperature sensor 7 that measures the temperature of the electrolyte inserted into the electrolyte, a calculation unit 8 that calculates the relationship between voltage and current at startup, etc., the relationship between the reference current and the electrolyte temperature, the reference voltage, and the electrolyte temperature. and a temperature compensation reference voltage, and a storage section 9 that stores the relationship between the temperature compensation reference voltage and the remaining capacity and supplies it to the calculation section 8, and a display section 10 that outputs the calculated remaining capacity and the like to the outside.

In the device shown in FIG. 7, when the power relay 4 is turned on, a large current flows through the starter motor, and the current pulsates as the starter motor rotates. At this time, the current I and voltage V were measured using an ammeter 5 and a voltmeter 6, respectively. The time interval for measurement is usually less than 1 second from when the starter motor is energized until the engine starts, and the pulsation period is 0.3.
Since the time is approximately seconds, it is desirable that the time be 0.1 seconds or less in order to obtain data from as wide a current range as possible.

In this example, a set of current and voltage (I, V,) (k=I to n) was measured at 0.03 second intervals at the same time as the starting current was flowing. A thermistor was used as the temperature sensor 7 used in the device of this embodiment. The output of the thermistor is sent to the calculation section along with voltage and current data.

The arithmetic unit 8 is composed of an IC circuit with excellent vibration resistance, heat resistance, and chemical resistance. The calculation unit 8 also serves as a controller that controls the storage unit 9 and the display unit 10.

The calculation unit 8 calculates the intercept V of a straight line indicating current/voltage characteristics based on the signal values sent from the voltmeter and ammeter. and the slope R was calculated by the method of least squares, and the VI straight line was determined. Furthermore, the relational expression (I) between the signal value sent from the temperature sensor 7, the temperature stored in the storage unit 9, and the reference current I3.

=96. Calculate the reference current I3 from O(1-0,72T), and calculate the reference voltage V3 (=V
o-R1,) was calculated. Furthermore, a temperature compensation reference voltage V is calculated from the relational expression V, =V, -0,0174T between the temperature compensation voltage 8 stored in the storage unit 9, the reference voltage v5, and the electrolyte temperature, and the temperature compensation reference voltage V is calculated from the relational expression V, =V, -0,0174T. The remaining capacity was calculated based on the relationship diagram (FIG. 6) between the voltage V and the remaining capacity. In this way, V, , R, T, L, V,
, V, and residual capacity are shown in Table 1.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between terminal voltage and discharge current density, Figure 2 is a diagram showing the relationship between discharge current and discharge time during starting, and Figures 3, 4, and 5 are diagrams at 0°C, 25°C, and 25°C, respectively. FIG. 6 is a diagram showing the relationship between the reference voltage V3 and the remaining capacity at 50° C., FIG. 6 is a diagram showing the relationship between the temperature-corrected reference voltage V2 and the remaining capacity, and FIG. 7 is a diagram showing a system for detecting the remaining capacity. DESCRIPTION OF SYMBOLS 1...Lead-acid battery, 2...Electrode, 3...Starter motor, 4...-Power relay 5...Ammeter, 7...Temperature sensor, 9...Storage part, 6 ... Voltmeter, 8... Calculation section, 10... Display section

Claims (1)

[Claims] The temperature of the lead-acid battery is measured, a reference voltage is calculated from the voltage-current relationship during large current discharge of the lead-acid battery, and a reference voltage is determined in advance based on the reference voltage and the battery temperature. The temperature compensation reference voltage at the battery temperature is calculated from the relationship between the battery temperature and the temperature compensation reference voltage, and the remaining capacity is determined from the relationship between the predetermined temperature compensation reference voltage and the remaining capacity of the lead-acid battery. Capacity detection method.