JPH04210738A - Battery pack - 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]

[00011

[Industrial Field of Application] The present invention relates to a battery pack using a rechargeable secondary battery. [0002] Nickel cadmium batteries are currently widely used as secondary batteries for battery packs. [0003] FIG. 5 shows a circuit diagram of a battery pack using a nickel-cadmium battery and a circuit diagram including a charger. A nickel cadmium battery 51 is built into a battery pack 52 and directly connected to a charger 53. [0004] I to a fully discharged nickel cadmium battery
FIG. 6 shows a graph of changes in terminal voltage and surface temperature of a nickel cadmium battery when charging is performed with a constant current of C. Here, "C" is a unit that indicates the ratio of current amount to battery capacity in a battery. Charging a battery with a battery capacity of IAh at IA is called IC charging, and charging at 2A is called 2C charging. [0005] In FIG. 6, the voltage between the terminals of the nickel cadmium battery increases during a period 61 as charging progresses. During this time, the electrical energy of the charging current is converted into chemical energy inside the battery, and charging progresses. [0006] At period 62, the battery becomes fully charged and its ability to store chemical energy reaches its limit. Therefore, the electrical energy of the charging current is no longer converted into chemical energy, but into thermal energy. As a result, the surface temperature of the battery increases. Along with this, nickel cadmium batteries have a characteristic that the charging terminal voltage decreases. This phenomenon is called the "-ΔV phenomenon" and is a characteristic of nickel-cadmium batteries that appears during charging and when fully charged. [0007] Overcharging is a problem that must be taken into account when charging a nickel cadmium battery. Overcharging increases battery temperature, rapidly deteriorating organic materials inside the battery, and significantly shortening battery life. [0008] Furthermore, when overcharging is performed with an excessive current, a large amount of gas is generated inside the battery, the safety valve is activated, and the electrolyte inside leaks to the outside. As a result, not only the battery capacity is drastically reduced, but also harmful substances are emitted. [0009] Therefore, when charging a nickel cadmium battery, it is necessary to decide whether to detect the fully charged state and reduce the charging current, or to continuously charge at a current amount that allows continuous charging even when fully charged. You need to use one of the methods.

[0010] The current that can be passed continuously in a fully charged state is usually
However, at this charging current, it takes more than 6 hours to fully charge a completely discharged battery. Furthermore, this charging method cannot be used when it is desired to fully charge the battery in a short time. I until the battery is fully charged
If a charging method is performed in which the battery is charged with C and after detecting full charge, the charging current is changed to a minute current, the battery can be fully charged from a completely discharged state in just over an hour. To detect full charge, it is common to use the "-ΔV phenomenon" which is a charging characteristic of nickel-cadmium batteries. Full charge is normally detected when the "-ΔV value" per cell of a nickel-cadmium battery is 10 mV to 20 mV. In a charging circuit like the one shown in FIG. 5, the charger side usually has a full charge detection function based on this "-ΔV" and has a function of switching the charging current to a minute current after detecting full charge. [00111 Nickel hydrogen battery has an electromotive force of 1 per cell.
．． At 2V, it is almost the same as a nickel cadmium battery. Nickel metal hydride batteries have energy density per unit volume,
Both energy density per unit weight exceeds that of nickel-cadmium batteries. In other words, it has the advantage that it can be used as a direct replacement for a nickel-cadmium battery and has a larger capacity than a nickel-cadmium battery. However, it has the disadvantage that it is difficult to control rapid charging. Its drawbacks are shown below. [0012] FIG. 7 shows a graph of changes in terminal voltage and battery surface temperature during IC charging of a nickel-metal hydride battery. [00131 In FIG. 7, the voltage between the terminals of the nickel-metal hydride battery increases during a period 71 as charging progresses. Operation during this period is the same as a nickel-cadmium battery. [0014] In the period 72, the battery becomes fully charged, and the surface temperature of the battery rises as in the case of a nickel-cadmium battery. However, compared to nickel-cadmium batteries, the charging terminal voltage "-△V voltage" is less, and it is 5 m per cell.
V or less. [0015] For this reason, it is not possible to accurately detect full charge just by monitoring the charging terminal voltage, and furthermore, the charger,
IC charging could not be performed unless the battery pack had a means for detecting the battery surface temperature. [0016] FIG. 8 shows an example of a conventional nickel-metal hydride battery pack and charger that can be charged with an IC.

The nickel-metal hydride battery 81 and the temperature sensor 82 each have their terminals extended to the outside of the battery pack 83, and are connected to the charger 8.
Connected to 4. The temperature sensor 82 is installed near the nickel-metal hydride battery 81 and detects the surface temperature of the nickel-metal hydride battery 81. The charger 84 detects changes in the charging terminal voltage of the nickel-metal hydride battery and the surface temperature of the nickel-metal hydride battery to detect full charge. [0018]

[Problem to be solved by the invention] However, as described above, by using a unique battery pack configuration for nickel-metal hydride batteries or by using a dedicated charger, compatibility with nickel-cadmium batteries, which is a characteristic of nickel-metal hydride batteries, can be achieved. I have to throw it away,
Chargers for nickel-cadmium battery packs will no longer be usable. [0019] Furthermore, three or more wires are required to connect the nickel-metal hydride battery pack and the dedicated charger, which poses a problem of restrictions when manufacturing the battery pack. [00201] An object of the present invention is to make the charging voltage characteristics of a nickel-metal hydride battery pack similar to those of a nickel-cadmium battery, so that full charge detection based on "-ΔV" can be reliably performed. [00211

[Means for Solving the Problems] The present invention provides a battery pack in which the change in surface temperature of a rechargeable secondary battery has a positive temperature gradient, and an equivalent resistance in series with the secondary battery that has a negative temperature gradient. It is characterized by connecting means. [0022] [Operation] By connecting an element with characteristics opposite to the gradient of temperature change on the surface of the battery, the surface temperature gradient is brought closer to linearity. [0023]

[Embodiment] An example of the battery pack of the present invention is shown in FIG. An equivalent resistance circuit 12 is connected in series to the nickel-metal hydride battery 11 and is exposed to the outside as a terminal. The equivalent resistance circuit 12 has a feature of having a negative temperature gradient with respect to the surface temperature of the nickel-metal hydride battery. [0024] An example of the equivalent resistance circuit 12 is shown in FIG. A thermally stable carbon film resistor 21 and a thermistor 22 are connected in parallel. The thermistor 22 is in close contact with the surface of the nickel-metal hydride battery 11. FIG. 3 shows the temperature-resistance characteristic of this equivalent resistance circuit 12. This characteristic is approximately linear over the surface temperature range of the battery used. [0025] The temperature-resistance characteristic of the thermistor is non-linear, and if all the charging current is passed through the thermistor, the thermistor will generate heat, making it impossible to accurately detect the battery surface temperature. Therefore, a circuit like the one shown in Figure 2 is used. Configure. [0026] FIG. 4 shows a graph of changes in voltage at various parts of the battery pack and battery surface temperature when constant current charging of the IC is performed on this battery pack in a fully discharged state. [0027] In period 41, the charging operation is progressing, and the inter-terminal voltage VB of the nickel-metal hydride battery 11 increases. The battery surface temperature remains constant. Therefore, resistance equivalent circuit 1
The resistance value of resistor 2 also remains constant, and the voltage VR across the resistor equivalent circuit 12 also remains constant. Therefore, the terminal voltage of the battery pack is
P rises. [0028] When period 42 begins, the nickel-metal hydride battery 11 becomes fully charged, and the terminal voltage VB of the battery 11 does not change. The battery surface temperature begins to rise. Therefore, the resistance value of the resistance equivalent circuit 12 decreases, and the voltage VR across the resistance equivalent circuit 12 decreases. Therefore, the terminal voltage VP of the battery pack
decreases. This corresponds to [-ΔV characteristic J. [0029] When IC constant current charging is performed, the movement of the voltage VP across this battery pack is the same as that of a nickel-cadmium battery. [00301] [Effect of the invention] By using the present invention as described above, the charging terminal voltage characteristics of the nickel-metal hydride battery pack become almost equal to the charging terminal voltage characteristics of the nickel-cadmium battery, and when the IC is charged at constant current, the Full charge can be detected by "V detection". [00311 As a result, the number of wires connecting the nickel-metal hydride battery pack and the charger can be reduced to two, and furthermore, the charger for the nickel-cadmium battery pack can be used as is. [0032]Furthermore, since full charge during IC constant current charging can be reliably detected, it is possible to prevent battery safety valve operation and battery deterioration due to overcharging.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a battery pack using the present invention.

FIG. 2 is a circuit diagram of the equivalent resistance circuit used in FIG. 1.

FIG. 3 is a graph showing temperature-resistance characteristics of the equivalent resistance circuit shown in FIG. 2;

FIG. 4 is a graph showing changes in voltage at various parts of the battery pack and battery surface temperature when constant current charging of an IC is performed on the battery pack of FIG. 1 in a fully discharged state.

FIG. 5 is a circuit diagram of a battery pack using a nickel-cadmium battery according to the prior art.

6 is a graph showing changes in terminal voltage and battery surface temperature when constant current charging of an IC is performed on the battery pack of FIG. 5 in a fully discharged state according to the prior art; FIG.

FIG. 7 is a graph showing changes in terminal voltage and battery surface temperature when constant current charging of an IC is performed on a fully discharged nickel-metal hydride battery according to the prior art.

[Figure 8] I using a nickel-metal hydride battery according to the prior art
A circuit diagram of a battery pack and charger capable of C charging.

[Explanation of symbols]

11.81 Nickel metal hydride battery 12... Equivalent resistance circuit 21... Carbon film resistor 22... Thermistor 51... Nickel cadmium battery 53.84
Charger 82... Temperature sensor

[Figure 1]

Claims (1)

[Claims] 1. A battery pack in which the change in surface temperature of a rechargeable secondary battery has a positive temperature gradient, characterized in that an equivalent resistance means having a negative temperature gradient is connected in series with the secondary battery. battery pack.