JPS63157078A - Method for detecting remaining capacity of lead-acid battery - Google Patents

Abstract

PURPOSE:To easily know the remaining capacity of a battery by measuring a terminal voltage V when the battery is discharged with current density of 100-400mA/cm<2>, a battery current I, and the liquid temperature of the battery, and finding differential internal resistance (V0-V)/I from the reference voltage V0 at the temperature. CONSTITUTION:The relation between the differential internal resistance obtained as a gradient and remaining capacity is found from the V-I (V: terminal volt age, I: battery current) at the time of large current discharging by using plural batteries whose remaining capacities are already known. Further, the tempera ture of the batteries is measured. Then, the voltage V, current I, and the liquid temperature of the battery when the battery is discharged while the discharging current density is 100-400mA/cm<2> are measured to find the reference voltage V0 at the temperature. Further, the differential internal resistance (V0-V)/I is found and the remaining capacity of an optional battery is known from the correlation between the differential internal resistance and remaining capac ity which are already found.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting the degree of deterioration of a lead-acid battery and the remaining capacity of the battery regardless of the state of charge.

(Prior Art) Conventionally, there is a method of determining the remaining capacity (discharge capacity) of a lead-acid battery by estimating it from measurements of electrolyte specific gravity, terminal voltage or internal resistance during high current short-time discharge, etc.

(Problems to be Solved by the Invention) However, the method of measuring the specific gravity of the electrolyte is complicated to operate, and a float serving as a specific gravity sensor or an electrode (Japanese Unexamined Patent Publication No. 60-29635) that detects specific gravity using a voltage signal is placed inside the battery. Even if it is incorporated into a battery, it requires modification of the battery itself, and it also has the drawback of being easily affected by temperature and maintenance (water replenishment, fluid replacement) conditions.

In the method of measuring terminal voltage during short-time discharge of large current (Japanese Patent Laid-Open No. 53-78029), the relationship between discharge capacity and terminal voltage cannot be obtained unless the measured current is limited to a specific value. Battery forklift battery or S
For LI (Starting.

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

In addition, in the method of measuring internal resistance, the voltage of a lead-acid battery is
This is because the current relationship is not a linear relationship.

A method using AC resistance (M,
llughes et al, Journal o
('^ppHedEIeetrochem1try
16.555 (198B)) is used, but AC resistance is difficult to measure when using batteries.

It has the disadvantage of requiring separate equipment for measurement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting the remaining capacity of a lead-acid battery that overcomes the drawbacks of the prior art described above.

(Means for Solving the Problem) According to the present invention, the correlation between the lead-acid battery temperature and the reference voltage is determined by determining the battery temperature, reference voltage, and differential internal resistance of a lead-acid battery whose remaining capacity is known. , and the correlation between the differential internal resistance and the remaining capacity, and the terminal voltage V when an arbitrary lead-acid battery is discharged at a current density within the range of 100 to 400 mA/c on the electrode surface, the battery Measure the current I and the temperature of the liquid in the battery, and determine the reference voltage V at the temperature based on the correlation between the liquid temperature and the reference voltage. is determined, and further the differential internal resistance (Vo-V)/I is determined, and the remaining capacity of any lead-acid battery is determined by the correlation between the differential internal resistance and the remaining capacity. The above objectives are achieved.

However, the reference voltage ■. is 100 to 4 per unit area of electrode.
Measure the terminal voltage (V1, V2,...) at each temperature when discharging for a short time at two or more current densities (discharge current: i, i2...) with different 00-^/C-. M1shi,
It is the voltage value at 1-0 obtained by linear extrapolation from the relationship of V-1 (I is the discharge current of the battery) of each battery, and the differential internal resistance is the voltage value per electrode tl area of a single cell of the battery. This is the slope of the V-1 straight line obtained when the discharge current density is in the range of 100 to 400 mA/c.

The basic idea of the present invention will be outlined below.

The relationship between the discharge current density (1) and the terminal voltage (■) of a lead-acid battery can be divided into two parts depending on the magnitude of the discharge current density, as shown in FIG. That is.

In the small current range, V decreases exponentially as i increases,
In a large current range, V decreases with respect to i in a linear function relationship.

The V-i relationship in the small current range occurs because the discharge reaction resistance is dominated by the activation overvoltage.

Unless the contribution of this activation overvoltage is removed, it is not possible to obtain a constant internal resistance that does not depend on the current from the V-i relationship.

Therefore, the discharge current density i is 100 m per unit area of the electrode.
By focusing on the fact that V-i has a linear relationship in the range of A/cj to 400mA/cj and finding that there is a good correlation between the differential internal resistance in this area and the remaining capacity of the battery, one aspect of the present invention was achieved. We have completed a method for detecting the remaining capacity of a lead-acid battery from the differential internal resistance during large current discharge.

(Preferred Embodiment) The method for detecting the remaining capacity of a lead-acid battery according to the present invention uses several batteries whose remaining capacities are known in advance, and the V-
1 (where I is the battery current) Find the relationship between the differential internal resistance obtained as the slope of the straight line and the remaining capacity, and then compare the differential internal resistance measured with any battery of the same type with the above relationship. This is a method for determining the remaining capacity of a battery at different electrolyte temperatures. Here, the differential internal resistance is per unit area of the electrode of a single battery cell (normally, the electrode of a lead-acid battery has one more negative electrode than the positive electrode, but the outer surface of the negative electrode placed at both ends is Since it is hardly working, it can be considered as the apparent area of the positive electrode), the discharge current density i is 1
V- obtained in the range of 00 to 400 mA/ci (1)
It is the slope of one straight line, and ■ is calculated using the terminal voltage of the assembled battery and ■ is the battery current.

In the lead-acid battery remaining capacity detection method of the present invention, the lead-acid battery used to obtain the correlation between the lead-acid battery temperature and the reference voltage and the differential internal resistance is measured in advance by a known remaining capacity measurement method. A lead-acid battery whose remaining capacity at the measurement temperature is known can be used. Known measuring methods and devices can be used to measure the temperature and voltage of the lead-acid battery. A known method can be used to discharge the lead-acid battery at a current density in the range of 100 to 400 mA/c at the electrode surface.

- For example, a constant current power source can be used to discharge a current that has the above-mentioned current density on the surface of the electrode.

In the method for detecting the remaining capacity of a lead-acid battery of the present invention, in order to determine the remaining capacity of an arbitrary lead-acid battery, discharging is performed at a current density within the range of 100 to 400 vA/C on the surface of the electrode. Any known method can be used without limitation, and a current such that a current density of "-" can be applied to the surface of the electrode using, for example, a constant current power source as described above. Also.

100~ when starting the engine, such as electric vehicle batteries, battery forklift batteries, or SLI batteries, etc.
If it is known that the battery is discharged at a current density within the range of 400 mA/cd, measurements can be made with the battery connected to the circuit and no special measures are required. - The relationship between differential internal resistance and remaining capacity will be explained below based on actual data.

New 55D23 type, N50Z type and N540Z^ type batteries or used batteries that have been used for 1 to 5 years as SLI rivers were tested at two large current densities i of ω and 0 under the battery temperature and residual capacity conditions shown in Table 1. Discharge for 5 seconds and the V-
The differential internal resistance of each battery was determined from the linear slope of I (where I is the battery current) and plotted against the remaining capacity in FIG. As shown in FIG. 2, there is a good correlation between the differential internal resistance and the remaining capacity, regardless of the battery temperature, the degree of battery deterioration, and the state of charge. Therefore, if the differential internal resistance of a battery of the same type in any state is known, the remaining capacity of the battery can be determined from the relationship shown in FIG. Next, we will discuss how to find the differential internal resistance of any battery.

As mentioned above, the differential internal resistance of a battery has a linear relationship between the terminal voltage V and the discharge current I in the discharge current density range of 100 to 400 mA/cj per unit electrode area of a single cell, and that V-1 (however, I (battery current) is determined from the slope of the straight line.

Therefore, basically, two or more points are required for the relationship between V and I when discharging at a large current for a short time. on the other hand.

SL! The battery is discharged at a large current density of 100 to 400 mA/c only when the engine is started, and it is almost never the case that the battery is discharged at two or more different large currents within a short period of time. However, if there is a reference voltage that is a point on the V-1 line and does not depend on the state of charge or the degree of deterioration of batteries of approximately the same rating, even a single large current discharge can be differentiated based on that reference voltage. resistance can be found. Fortunately, such a reference voltage existed at the point (V in FIG. 1) where the V-1 straight line in the large current discharge region was extrapolated to the current 1-0. In other words, the V-1 (where I is the battery current) straight line obtained in the experiment shown in Table 1! The voltage value V extrapolated to -0. It has been found that it is possible to converge to a nearly constant value regardless of the type of battery, state of charge, and degree of deterioration.

Figure 3 shows the obtained V. The value of is shown against battery temperature. Therefore, if you measure the temperature of the battery, the V corresponding to that temperature. Using the value of , the remaining capacity of the battery can be determined from the relationship shown in FIG. 2, which occurs only once.

The discharge current density for measuring the differential internal resistance in the method for detecting the remaining capacity of a lead-acid battery of the present invention is 100 to 4.
The range is preferably 00gA/c-, 100*A/
If it is less than cj, the activation overvoltage will affect the differential internal resistance and the remaining capacity will not correspond. On the other hand, the upper limit current density varies depending on the remaining capacity of the battery, but is 400
If it is more than mA/cd, the voltage drop may become large with respect to the energization time, and the all constant error cannot be ignored, which is not preferable. As long as the current density is within the above-mentioned current density range, the voltage is relatively stable for up to 5 seconds after the start of current flow, and it is desirable to measure the voltage during this period.

Note that the remaining capacity in the present invention is expressed as a 5 hour rate (5HR) capacity. The discharge capacity (residual capacity) of a battery changes depending on the magnitude of the discharged current, and the larger the discharge current, the lower the discharge capacity that can be taken out. Therefore, the discharge capacity is generally expressed as a 5-hour rate discharge capacity or a 20-hour rate discharge capacity by indicating the magnitude of the discharge current. Here, the 5 hour rate and 20 hour rate are the nominal capacity of a new batteryff
It means the current value at which i (Ah) is completely discharged at each time.

This current dependence of discharge capacity occurs because the electrodes of lead-acid batteries are porous plates, and as the discharge current increases, the discharge reaction concentrates only near the surfaces of the positive and negative electrodes, and the active material inside the electrodes becomes more concentrated. This is because it is not used effectively. However, since there is a substantially constant relationship between the discharge capacity at each time rate, the discharge capacity of a battery is usually expressed as a 5-hour rate capacity or a 20-hour rate capacity. Therefore, the 5-hour rate capacity was used as the remaining capacity in the present invention.

Table 1 (Example) In order to demonstrate the effectiveness of the method for detecting the remaining capacity of a lead-acid battery according to the present invention, an experiment was conducted using the test circuit shown in FIG. 4. Test battery 4
0 has a new 55D23 type battery and! A total of 5 batteries, 115oZ type used batteries and 3 N540ZA type used batteries, were used and discharged for 1 to 5 seconds while changing the battery temperature, charging state, and discharge type*1. The experimental conditions are summarized in Table 2. From the battery temperature T determined using the thermometer 42 in each test, the corresponding ■ is determined using FIG. 3, and this V is determined. And constant current electricity? Discharge current I measured by R43 and voltmeter 41
Calculate the differential internal resistance of the battery using the 1st grain battery voltage V or the 5th grain battery voltage 1 second × 5 seconds measured by
The remaining capacity of the battery was determined in accordance with the solid line in FIG. Table 2 shows the remaining capacity calculated from 71 seconds or 5 seconds from V. There is no significant difference between the two, and both values are extremely close to the residual capacity adjusted before the test, thus proving the effectiveness of the method for detecting the residual capacity ffi of a lead-acid battery according to the present invention.

Table 2 (Functions and Effects) In the present invention, the differential internal resistance in the large current discharge region, which has been found to have a good correlation with the remaining capacity of the battery, includes the resistance of the discharge reaction (resistance based on diffusion overvoltage).

Factors that are related to the deterioration of the electrode and the state of charge, such as the surface area of the active materials, the contact resistance between the active materials, and the resistance of the lattice, and which can be treated as pure resistance, contribute. Therefore, it is considered that there is a good correlation with the remaining capacity regardless of the degree of deterioration of the battery or the state of charge. Also, the reference voltage V. The introduction of this has a great advantage in that it makes it possible to calculate the differential internal resistance with a single discharge at an arbitrary large current, making it extremely easy to detect the remaining capacity of the battery.

The method for detecting the remaining capacity of a lead-acid battery according to the present invention has been described above.

Whether it is an electric vehicle battery, battery forklift battery, or SLI battery, the remaining capacity of the battery can be easily determined from the voltage-current of the battery when a large current is discharged when the battery is connected to an electric circuit. It can be used, and its utility value in applied fields is extremely large.

[Brief explanation of the drawing]

Figure 1 shows the reference voltage V. Conceptual diagram. FIG. 2 is a diagram showing the relationship between differential internal resistance and remaining capacity. Figure 3 shows the reference voltage■. A diagram showing the temperature dependence of. FIG. 4 is an example of a test circuit for obtaining the voltage-current relationship. Applicant Toyota Central Research Institute Co., Ltd. Agent Patent attorney Asami Kato (1 other person) Figure 1 Discharge current density i (mA/cj) Figure 3-2002040e, Q Battery temperature (°C)

Claims (1)

[Claims] By determining the battery temperature, reference voltage, and differential internal resistance of a lead-acid battery whose remaining capacity is known, the correlation between the lead-acid battery temperature and the reference voltage, and the relationship between the differential internal resistance and the remaining capacity can be determined. Terminal voltage V, battery current I, and liquid temperature of the battery when an arbitrary lead-acid battery is discharged at a current density within the range of 100 to 400 mA/cm^2 at the electrode surface. and determine the reference voltage V_0 at the temperature based on the correlation between the liquid temperature and the reference voltage,
A residual capacity detection method for a lead-acid battery that further determines the differential internal resistance (V_0-V)/I and determines the residual capacity of an arbitrary lead-acid battery based on the correlation between the differential internal resistance and the residual capacity. (However, the reference voltage V_0 is 100% per unit area of the electrode.
Two or more different current densities of ~400mA/cm^2 (
The terminal voltage (V_1, V_2, ...) when discharging for a short time with discharge current: i_1, i_2, ...) was measured at each temperature, and the V-I of each battery (I is the discharge of the battery) was measured at each temperature. It is the voltage value at I=0 obtained by linear extrapolation from the relationship (current), and the differential internal resistance is the voltage value when the discharge current density per unit area of the electrode of a single cell of the battery is 100 to 400 mA/c.
This is the slope of the VI straight line obtained in the range of m^2. )