JPH04274776A - Detecting device of lifetime of ni-cd storage battery - Google Patents

Abstract

PURPOSE:To enable objective detection of the lifetime of an Ni-Cd battery by knowing only the lowering of capacity due to only a true factor of deterioration. CONSTITUTION:The time from start of charging to detection of - V is measured by a time measuring circuit 10 and the measured time for detection of - V is compared with the time for detection of - V at the end of lifetime which is set beforehand as a table value, so as to determine the lifetime. Factors due to the temporary lowering of capacity caused by a change in the capacity due to a change in a load of a device, the effect of an ambient temperature at the time of charging discharging and inactivation are removed, the lowering of the capacity due to only a factor of deterioration is comprehended accurately, and this is made known at the time of the end of the lifetime.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ni--Cd storage battery life detection device, and is particularly suitable for use in a constant current -ΔV detection type charger with a discharging function.

0002

2. Description of the Related Art FIG. 4 is a graph showing the discharge characteristics of a sealed Ni--Cd storage battery (hereinafter simply referred to as Ni--Cd storage battery), and shows the voltage change with respect to time when discharging at a constant current. When discharging a Ni-Cd storage battery, the lowest allowable voltage is called the end-of-discharge voltage, and generally the end-of-discharge voltage per cell of a Ni-Cd storage battery is 1.0.
It is V.

As is clear from FIG. 4, the larger the discharge current value is, the shorter the time it takes for the battery voltage to drop to the discharge end voltage. In general, the discharge capacity of Ni-Cd storage batteries (
Capacity (hereinafter simply referred to as capacity) is expressed as the product of the time from the start of discharge until reaching the final voltage and the discharge current value, and is
It is expressed in units of h (ampere hour) or mAh (milliamp hour). Further, although the nominal capacity of Ni-Cd storage batteries is determined for each type of battery, this value is based on the capacity when discharged with a 0.2C current.

[0004] Here, C of 0.2C is a numerical value representing the nominal capacity of a battery, and charging/discharging current is generally expressed using a multiple of this value. For example, 0.1 for a 120mAh battery
C current is 1200×0.1=120mA. However, the capacity actually obtained by discharging varies depending on the magnitude of the discharge current and the ambient temperature. That is, Figure 5
As shown in the characteristic diagram of discharge rate and discharge capacity, as the discharge current increases, the utilization rate of the electrode plate active material decreases, so the discharge efficiency decreases and the capacity that can actually be extracted from the battery decreases.

Furthermore, as shown in the discharge temperature characteristic diagram in FIG. 6, when discharging at low temperatures, the reaction of the active material within the battery decreases, so the internal resistance increases, the discharge voltage decreases, and the discharge capacity also decreases. Decrease. This tendency increases as the discharge current increases. However, this decrease in capacity is a temporary deterioration in performance, and the capacity will be restored by charging and discharging at room temperature. Also,
As shown in the charging temperature characteristic diagram of FIG. 7, even during charging, charging efficiency decreases when charging at high temperatures, resulting in a decrease in discharge capacity. However, this decrease in capacity is also a temporary deterioration in performance, and the characteristics will return to their original state if the battery is returned to room temperature and charged.

Furthermore, in batteries that have been repeatedly subjected to shallow charge/discharge cycles, or batteries that have been left in a charged state for a long period of time, the internal resistance has increased due to the inactivation of the active material. The voltage drop is significantly larger than that of normal batteries, and the discharge capacity is also reduced. However, the characteristics can be restored to normal by repeating discharging and charging several times.

By the way, Ni--Cd storage batteries have the characteristic that as the number of charging and discharging increases, in addition to the temporary capacity reduction as described above, the capacity decreases irreversibly due to deterioration. The causes of the above capacity decrease include a decrease in electrode plate performance, deterioration of the separator, and a decrease in electrolyte, but depending on the temperature conditions during use, charging/discharging pattern, and frequency of use,
The type of cause and the period until the end of life are different.

[0008] Generally, the lifespan of a Ni-Cd storage battery is defined as the point at which the battery capacity decreases to 50% or less of the nominal capacity and is no longer recovered, but the criteria for determining the actual lifespan vary depending on the application. . In practice, you can set a function that generates an alarm when the lowest usable voltage is reached on a battery-powered device, and then repeat the usage state of recharging when the alarm occurs, allowing you to operate the device until the alarm occurs. If the time becomes extremely short or a certain amount of work cannot be completed with one charge, and the condition does not change even after recharging, the operator may indicate that the battery used has reached the end of its life. It was determined that there was.

On the other hand, one of the charging methods for Ni--Cd storage batteries is a -ΔV voltage detection method. When quickly charging a Ni-Cd storage battery for quick charging, this method detects the voltage drop (referred to as -△V) after the battery voltage reaches its peak value at the end of charging and cuts off the charging voltage. This is a device that prevents overcharging. This is because, as a characteristic of the Ni-Cd storage battery, the battery temperature rises due to gas consumption during the charging completion stage, and as the battery voltage passes through its peak point, the voltage drops. Charging is terminated by capturing this characteristic, and it has the advantage of being able to charge effectively in a short period of time. Furthermore, in addition to this method, there is a charger that has a function of discharging the residual charge of the battery before charging, thereby eliminating the above-mentioned temporary capacity reduction due to the influence of ambient temperature or inactivation.

An example of a charger that charges by this method is shown in the block diagram of FIG. 3, and FIG. 2 shows a graph of the discharge and charge characteristics of the charger. The voltage of the Ni-Cd storage battery 1 is detected by the voltage detection circuit 2, and the discharge end voltage VE (
In the case of a 4-cell assembled battery, if the voltage is higher than approximately 4.0 V), the selector switch 3 is connected to the discharge load side 4, and the transition is as shown in the discharge voltage curve (1) and discharge current curve (4) in Figure 2. discharge to the discharge end voltage VE.

[0011] Then, the voltage of the battery 1 reaches the discharge end voltage VE
When the voltage detection circuit 2 switches the switching state of the switch 3 from the discharging load 4 side to the charging current control circuit 8 side, a charging current is caused to flow from the constant current DC source 5 to the Ni-Cd storage battery 1. Changes in charging voltage and charging current in a normal battery at this time are as shown in curves (2) and (5) in FIG. On the other hand, changes in charging voltage and charging current in an abnormal battery are as shown in curves (3) and (6) in FIG. At the same time, the voltage storage circuit 6 is reset by the reset circuit 9, and the battery voltage detected by the voltage detection circuit 2 is outputted to one of the two input terminals of the voltage comparison circuit 7 and the voltage storage circuit 6.

The voltage input to the voltage storage circuit 6 is held for a certain period of time and is output to the other input terminal of the voltage comparison circuit 7. The voltage comparison circuit 7 successively compares the two input voltages, and when the input voltage from the voltage detection circuit 2 is lower than the input voltage from the voltage storage circuit 6 by △V, the time t is determined.
2, an instruction is given to the charging current control circuit 8 to cut off the charging current, and charging is terminated.

[0013]

[Problems to be Solved by the Invention] However, the above-mentioned lifespan determination has the following problems. First, as mentioned above in the prior art section, Ni
-Cd storage batteries have characteristics that discharge efficiency varies depending on the magnitude of discharge current, and the capacity that can be extracted also varies. However, in devices where batteries are actually used, - the processing content for charging is fixed each time, and the processing time or processing amount for a normal battery is known in advance with this as the basic pattern, and the processing time or processing amount for a normal battery is known in advance, and Not all conditions can be compared on the same basis as processing time or processing amount. Therefore, if the load fluctuation is not constant and the load fluctuation is not constant, the discharge efficiency will also change in a complicated manner.
Since the processing content differs each time the battery is charged, there is a problem in that it is not possible to accurately determine the actual capacity of the battery.

Second, temporary capacity reduction due to the influence of ambient temperature during charging and discharging and inactivation must be judged separately from irreversible capacity reduction due to deterioration, which is a factor in determining the original lifespan. . However, many devices that use Ni--Cd storage batteries as power sources are portable devices that cannot be powered by an AC line, and are also susceptible to changes in ambient temperature. Furthermore, repeated shallow charging and discharging and long-term storage in a charged state for three months or more, which can cause inactivation, are common conditions in actual use. Therefore, it is difficult to remove these effects. Therefore, in order to recover from the temporary decrease in capacity caused by these, there is a problem in that unless the battery is discharged and charged several times at room temperature, the original lifespan cannot be determined.

Thirdly, in actual operation, as mentioned above, the time or amount of a certain amount of processing is used as a guideline for determining the lifespan, but the determination of the lifespan is ultimately based on the experience of the human operator. , since intuitive judgment is the deciding factor and wins, it cannot be said to be a quantitative judgment, and it was not a technically satisfactory lifespan detection method. In view of the above-mentioned problems of the present invention, Ni
- It is an object of the present invention to objectively detect the lifespan of a Cd storage battery by grasping only the amount of capacity decrease due to only true deterioration factors.

[0016]

[Means for Solving the Problems] The Ni-Cd storage battery life detection device of the present invention includes a time measurement circuit that measures the time required from the time when charging of the Ni-Cd storage battery is started until -ΔV detection, and the above-mentioned Compare the comparison data table for setting comparison time data for determining that the Ni-Cd storage battery has reached the end of its life, and the time data derived from the time measurement circuit and the time data derived from the comparison data table. a time comparison circuit that determines the lifespan of the Ni-Cd storage battery, and a lifespan display circuit that displays that the Ni-Cd storage battery has reached the end of its lifespan based on a lifespan display signal derived from the time comparison circuit. are doing. Another feature of the present invention is that a data changing circuit is provided for varying the comparison time data set in the comparison data table.

[0017]

[Function] The time measuring circuit measures the time from the start of charging until -△V detection, and the measured -△V detection time and -△V at the end of life, which is set in advance as a table value.
By comparing the detection time and determining the lifespan, it is possible to eliminate factors such as capacity fluctuations due to device load fluctuations, the influence of ambient temperature during charging and discharging, and temporary capacity decreases due to inactivation. This enables accurate battery replacement that is not influenced by the operator's intuition by accurately determining the amount of capacity reduction caused solely by deterioration factors.

[0018]

[Embodiment] FIG. 1 is a circuit block diagram showing an embodiment of the Ni-Cd storage battery life detection device of the present invention. The circuit configuration is exactly the same as that of the charger, and detailed explanation will be omitted. In FIG. 1, −
The ΔV detection signal S1 is provided to the charging current control circuit 8 and also to the time measurement circuit 10. Then, in the time measurement circuit 10, the charging start time t1 in FIG.
The time required from -ΔV detection time t2 is measured,
This is output to the time comparator circuit 12 as required time data S2.

On the other hand, in the comparison data table 11, Ni
-△V detection time for determining that the -Cd storage battery has reached the end of its service life (
(corresponding to tl in FIG. 2) is set in advance as comparison time data S3, and these time data S2 and S3 are compared by the time comparison circuit 12. As a result of this comparison, the output data S2 from the time measurement circuit 10 is higher than the output data S3 from the comparison data table 11.
is smaller (as in t2' in FIG. 2), it is determined that the charged battery has reached the end of its life, and the time comparison circuit 12 outputs a life display instruction signal S4 to the life display circuit 13. The life display circuit 13 receives this signal S4 and displays that the battery has reached the end of its life.

[0020] By always discharging the residual charge before charging, the second problem mentioned above, which is a temporary decrease in capacity due to the influence of ambient temperature and inactivation, is eliminated, which is an unnecessary factor for life detection. can do. Furthermore, since all charging starts from the discharge end voltage and is charged with a constant current, the time until -ΔV is detected is proportional to the pure battery capacity. However, it is assumed that the discharging/charging environment here is always at room temperature, but since such discharging/charging devices are generally stationary, they are installed indoors and may be placed in a favorable temperature environment. many. From this, depending on the individual device that uses batteries,
By determining in advance the -ΔV voltage detection time of a battery that can be determined to be at the end of its lifespan and setting it in the data table 11 of FIG. 1, the lifespan can be easily, quantitatively and objectively detected at the same time as charging.

Furthermore, by adding the data changing circuit 14 as shown in FIG. 1, it becomes possible to freely set the life detection time in accordance with the operation of the device in the comparison data table 11, which makes it possible to This enables versatile life detection.

[0022]

Effects of the Invention As described above, the present invention includes a time measurement circuit that measures the time from the start of charging to -△V detection, and a -△V detection time measured by the time measurement circuit that is set in advance as a table value. −△
a time comparison circuit that compares the V detection time to determine the lifespan;
A lifespan display circuit is provided to display the results determined by the time comparison circuit. Therefore, it is possible to grasp the lifespan of the Ni-Cd storage battery quantitatively and objectively, and when the lifespan has come to an end, it can be reliably notified, making it possible to implement optimal operability through accurate battery replacement. can. Further, according to the invention of claim 2, since a circuit is provided that can vary the table value for setting -ΔV detection time at the end of life, the life detection time can be freely varied according to the operation mode of the device. Flexible and versatile support is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a discharge function monthly constant current -ΔV detection type charger showing an embodiment of the Ni-Cd storage battery life detection device of the present invention.

[Fig. 2] Release and release diagram for explaining the operation of the charger of this embodiment.
It is a charging characteristic diagram.

FIG. 3 is a circuit block diagram of a conventional constant current -ΔV detection type charger with a discharging function.

FIG. 4 is a discharge voltage characteristic diagram of the charger of FIG. 3;

FIG. 5 is a characteristic diagram showing the relationship between the discharge rate and discharge capacity of the charger of FIG. 3;

FIG. 6 is a characteristic diagram showing the discharge temperature characteristics of the charger of FIG. 3;

FIG. 7 is a characteristic diagram showing charging temperature characteristics of the charger of FIG. 3;

[Explanation of symbols]

1 Ni-Cd storage battery 10 Time measurement circuit 11 Comparison data table 12 Time comparison circuit 13 Lifetime display circuit 14 Data change circuit S1 -ΔV detection signal S2 Required time data S3 Comparison time data S4 Life display instruction signal

Claims (2)

[Claims] Claim 1: A time measurement circuit that measures the time required from the time when charging of the Ni-Cd storage battery is started until -ΔV is detected, and comparison time data for determining that the Ni-Cd storage battery has reached the end of its service life. a comparison data table for setting, and a time comparison circuit that compares the time data derived from the time measurement circuit and the time data derived from the comparison data table to determine the lifespan of the Ni-Cd storage battery; A lifespan display circuit that displays that the Ni-Cd storage battery has reached the end of its lifespan based on a lifespan display signal derived from the time comparison circuit.
- Life detection device for Cd storage battery. 2. The Ni--Cd storage battery life detection device according to claim 1, further comprising a data changing circuit for varying the comparison time data set in the comparison data table.