JP3173012B2 - Battery pack, charging device and charging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery pack using a rechargeable secondary battery.

[0002]

2. Description of the Related Art At present, nickel cadmium batteries are widely used as secondary batteries used in battery packs.

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 contained in a battery pack 52 and is directly connected to a charger 53.

[0004] A fully discharged nickel cadmium battery
FIG. 6 is a graph showing changes in the inter-terminal voltage and the surface temperature of the nickel cadmium battery when charging was performed at a constant current of C. Here, “C” is a unit indicating the ratio between the amount of current and the battery capacity in a battery. Charging 1A for a battery having a battery capacity of 1Ah is called 1C charging and 2A charging.
Charging is referred to as 2C charging.

In FIG. 6, the voltage between the terminals of a nickel cadmium battery increases during the period 61 as the charging proceeds. During this time, the electric energy of the charging current is converted into chemical energy inside the battery, and charging proceeds.

In the period 62, the battery is fully charged, and the ability to store chemical energy reaches its limit. For this reason, the electrical energy of the charging current is no longer converted into chemical energy, but is converted into thermal energy. As a result, the surface temperature of the battery increases. Accordingly, the nickel cadmium battery has a characteristic that the charging terminal voltage decreases. This phenomenon is called "-△ V phenomenon", and during charging,
This is a feature of nickel cadmium batteries that appear when fully charged.

[0007] One problem that must be noted when charging nickel cadmium batteries is overcharging. When overcharging is performed, the battery temperature rises, the organic substances inside the battery rapidly deteriorate, and the battery life is significantly shortened.

Further, when overcharging is performed with an excessive current, a large amount of gas is generated inside the battery, and the safety valve operates to leak the electrolyte inside. As a result, not only the battery capacity is extremely reduced, but also harmful substances are released.

Therefore, when charging a nickel cadmium battery, it is necessary to reduce the charging current by detecting a fully charged state, or to continuously charge the battery with a current amount that can be continuously charged even when fully charged. You need to take one of these measures.

The current that can be continuously passed in a fully charged state is usually
Up to 0.2 C, but at this charge current it takes more than 6 hours to fully charge a fully discharged battery.
If the battery is to be fully charged in a shorter time, this charging method cannot be used. 1 until the battery is fully charged
If charging is performed by charging the battery at C and detecting a full charge and then changing the charging current to a very small current, the battery can be fully charged in just over an hour from a completely discharged state. For detecting full charge, it is common to use the “−ΔV phenomenon” which is a charge characteristic of a nickel cadmium battery. Normally, full charge detection is performed when the “−ΔV value” per nickel cadmium battery cell is 10 mV to 20 mV. In the charging circuit shown in FIG. 5, it is usual that the charger side has a function of detecting full charge by this "-.DELTA.V", and has a function of switching the charging current to a small current after detecting the full charge.

The nickel-metal hydride battery has an electromotive force of 1.2 V per cell, which is almost the same as the nickel-cadmium battery.
Nickel-metal hydride batteries have an energy density per unit volume,
The energy density per unit weight exceeds that of nickel cadmium batteries. That is, there is an advantage that the nickel cadmium battery can be used as it is, and the capacity is larger than that of the nickel cadmium battery. However, on the contrary, there is a disadvantage that it is difficult to control the rapid charging. The disadvantages are described below.

FIG. 7 is a graph showing changes in the inter-terminal voltage and the battery surface temperature during 1C charging of a nickel-metal hydride battery.

In FIG. 7, the voltage between the terminals of the nickel-metal hydride battery increases during the period 71 as the charging proceeds. The operation during this period is the same as that of the nickel cadmium battery.

In the period 72, the battery is fully charged, and the surface temperature of the battery rises as in the case of the nickel cadmium battery. However, the charge terminal voltage “−ΔV voltage” is smaller than that of the nickel cadmium battery, which is 5 to 5 per cell.
mV or less.

For this reason, accurate monitoring of the full charge cannot be performed simply by monitoring the charge terminal voltage.
1C charging could not be performed without a battery surface temperature detecting means on the battery pack side.

FIG. 8 shows an example of a conventional nickel hydrogen battery pack and a charger capable of 1C charging.

The nickel-metal hydride battery 81 and the temperature sensor 82 output terminals to the outside of the battery pack 83, respectively.
4 is connected. 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 a change in the charging terminal voltage of the nickel-metal hydride battery and a change in the surface temperature of the nickel-metal hydride battery to detect full charge.

[0018]

However, as described above, the compatibility with the nickel cadmium battery, which is a feature of the nickel hydride battery, can be achieved by using a unique battery pack configuration of the nickel hydride battery or using a dedicated charger. Will be thrown away,
Nickel cadmium battery pack chargers will no longer be usable.

Further, there is a problem that three or more wires for connecting the nickel-metal hydride battery pack and the dedicated charger are required, which is a restriction when manufacturing the battery pack.

An object of the present invention is to make the charge voltage characteristic of a nickel-metal hydride battery pack similar to the charge voltage characteristic of a nickel cadmium battery, so that full charge detection by "-ΔV" can be reliably performed.

[0021]

The battery pack of the present invention comprises:
A secondary battery, means for converting the temperature of the secondary battery into a resistance value, wherein the resistance value has a temperature resistance conversion means having a negative temperature gradient, and a set of one for charging the secondary battery; A terminal, and the secondary battery and the temperature resistance conversion means are connected in series between the pair of terminals. Further, the charging device of the present invention is a charging device for charging a secondary battery, wherein the means for converting the temperature of the secondary battery into a resistance value, wherein the resistance value has a negative temperature gradient. Means, a set of terminals for charging the secondary battery, a terminal between which the secondary battery and the temperature resistance conversion means are connected in series, and charging between the terminals. It is characterized by comprising a means for applying a current and a charge detecting means for detecting a state of charge of the secondary battery according to a voltage between the terminals. Furthermore, the charging method of the present invention includes a secondary battery and a temperature-resistance conversion unit that converts the temperature of the secondary battery into a resistance value with a negative temperature gradient, A charging method for charging the secondary battery by applying a charging current to both ends connected in series with the means; Switching the current to a very small current.

[0022]

An element having a characteristic reverse to the gradient of the temperature change on the battery surface is connected to make the surface temperature gradient linear.

[0023]

FIG. 1 shows an example of a battery pack according to the present invention. An equivalent resistance circuit 12 is connected in series to the nickel-metal hydride battery 11 and is provided as a terminal to the outside. The equivalent resistance circuit 12 has a feature that it has a negative temperature gradient with respect to the surface temperature of the nickel-metal hydride battery.

FIG. 2 shows an example of the equivalent resistance circuit 12. 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 a temperature-resistance characteristic of the equivalent resistance circuit 12. This characteristic is approximately linear over the surface temperature range of the battery used.

Since the temperature-resistance characteristic of the thermistor is non-linear, and if the entire charging current is supplied to the thermistor, the thermistor generates heat and cannot accurately detect the battery surface temperature. Configure.

FIG. 4 is a graph showing changes in the voltage of each part of the battery pack and the battery surface temperature when the battery pack in a completely discharged state is charged at a constant current of 1 C.

In the period 41, the charging operation is in progress, and the terminal voltage VB of the nickel-metal hydride battery 11 increases. The battery surface temperature remains constant. Therefore, resistance equivalent circuit 1
2, the voltage VR across the resistance equivalent circuit 12 is also constant. Therefore, the terminal voltage V of the battery pack
P rises.

In the period 42, the nickel-metal hydride battery 11 is fully charged, and the terminal voltage VB of the battery 11 does not change. The battery surface temperature starts 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 the “−ΔV characteristic”.

When 1 C constant current charging is performed, the voltage VP at both ends of the battery pack moves in the same manner as a nickel cadmium battery.

[0030]

As described above, when the present invention is used, the charging terminal voltage characteristic of the nickel-metal hydride battery pack becomes substantially equal to the charging terminal voltage characteristic of the nickel cadmium battery, and the "-.DELTA. To detect full charge.

As a result, the number of lines connecting the nickel-metal hydride battery pack and the charger can be reduced to two, and further, there is an effect that the charger of the nickel-cadmium battery pack can be used as it is.

Further, since the full charge at the time of 1C constant current charging can be reliably detected, there is an effect that the safety valve operation of the battery due to overcharge and the deterioration of the battery can be prevented.

[Brief description of the drawings]

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

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

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

FIG. 4 is a graph showing changes in the voltage of each part of the battery pack and the battery surface temperature when the battery pack of FIG. 1 in a completely discharged state is charged at a constant current of 1C.

FIG. 5 is a circuit diagram of a battery pack using a conventional nickel cadmium battery.

6 is a graph showing changes in terminal voltage and battery surface temperature when a constant current charge of 1 C is performed on the battery pack of FIG. 5 in a completely discharged state according to the related art.

FIG. 7 is a graph showing changes in terminal voltage and battery surface temperature when a 1 C constant current charge is performed on a nickel-metal hydride battery in a completely discharged state according to the related art.

FIG. 8 shows a conventional battery using a nickel-metal hydride battery.
FIG. 3 is a circuit diagram of a battery pack and a 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

Claims (3)

(57) [Claims] 1. A rechargeable battery, means for converting the temperature of the rechargeable battery into a resistance value, and a temperature resistance conversion means having a negative temperature gradient with the resistance value, and charging the rechargeable battery A battery pack comprising: a set of terminals for connecting the secondary battery and the temperature resistance conversion means in series between the set of terminals. 2. A charging device for charging a secondary battery, comprising: means for converting the temperature of the secondary battery into a resistance value;
The resistance value is a temperature resistance conversion means having a negative temperature gradient, and a set of terminals for charging the secondary battery,
A terminal between which the secondary battery and the temperature resistance conversion means are connected in series; a means for applying a charging current between the terminals; and a charging of the secondary battery according to a voltage between the terminals. A charging device comprising: charging detection means for detecting a state. 3. A rechargeable battery, comprising: a rechargeable battery; and a temperature-resistance converting means for converting a temperature of the rechargeable battery into a resistance value with a negative temperature gradient. In the charging method of charging the secondary battery by adding a charging current to both ends connected in series, a step of measuring a voltage of the both ends, and a step of measuring the charging current when a voltage drop is detected in the voltage measuring step. Switching to a very small current.