JP2002315178A - Method for preventing overcurrent of battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely eliminate generation of a useless load on a battery by keeping the resistance of an overcurrent protective element at an initial value when the cause of generating an overcurrent is removed and a normal state is recovered. SOLUTION: In a method for lowering an average current Ix by switching conduction on/off upon occurrence of an overcurrent, the on/off time ratio t1/t2 is varied such that the average current decreases as the overcurrent increases.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for preventing overcurrent of a battery, particularly a secondary battery.

[Prior art]

Recently, notebook personal computers, information terminals,
2. Description of the Related Art Secondary batteries having a large volume energy density, for example, lithium ion secondary batteries, are frequently used as power sources for video tape recorders, digital cameras, portable electronic devices such as mobile phones, electric vehicles, and the like. This secondary battery is used in the form of a battery pack in which a protection circuit for preventing overcharge and discharge and a battery are packaged, and the protection circuit includes, for example, a switching circuit for preventing overcharge and overdischarge. , A main control circuit for detecting an abnormality during charging / discharging and operating the switching circuit, a current detection circuit for detecting a circuit current, a fuse cutoff circuit, and a main control circuit for detecting an abnormality and performing switching. It comprises an auxiliary control circuit and the like for activating the fuse cutoff circuit when the current detection circuit detects the non-operation of the switching circuit despite issuing an operation command to the circuit.

In the above-described secondary battery having a high energy density, when an abnormality such as a short circuit occurs, since the battery itself contains a large amount of energy, the battery itself generates a large amount of heat, and in an extreme case, the battery container explodes. Therefore, prevention of overcurrent is extremely important. Conventionally, a thermistor (polyswitch) is used as an overcurrent prevention element, and the overcurrent is suppressed by increasing the resistance value due to heat generation of the thermistor itself due to the overcurrent.
In the above, when the battery is restored to the normal state, the use of the battery is continued. On the other hand, when the normal condition is not restored, or when the same abnormality occurs again within a short time only after the temporary recovery, the battery pack is discarded by operating the fuse cutoff circuit. ing.

[0004]

In the overcurrent prevention method using the above-mentioned thermistor, the resistance value of the thermistor often becomes higher than the initial resistance value even if the normal state is restored, so that a wasteful load is imposed on the battery. Often leads to energy loss.

An object of the present invention is to provide a method for preventing overcurrent in a battery, in which when the battery is restored to a normal state, the resistance value of the overcurrent protection element is kept at an initial value, and a wasteful load is applied to the battery. It is to eliminate the occurrence of the problem.

[0006]

The method of preventing overcurrent of a battery according to the present invention is a method of reducing the average current by turning on / off current when an overcurrent occurs. The larger the overcurrent is, the lower the average current is. The on / off time ratio is changed so that the overcurrent can be turned on / off by a bimetal switch. As the bimetal switch, a Cu--Ni--Mn alloy piece and a Fe--Ni alloy piece are used. Laminated bimetals are preferred.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an overcurrent protection element used in the present invention. In FIG. 1, reference numeral 1 denotes an insulating block having a step, for example, a resin block. Reference numeral 2 denotes a bimetal in which a low thermal expansion coefficient metal piece 21 and a high thermal expansion coefficient metal piece 22 are laminated, and one end is fixed to a high end of the insulating block 1 in a cantilever manner. Reference numeral 3 denotes a terminal electrode such as a copper plate, which is fixed to the lower side of the insulating block 1. Reference numeral 42 denotes a contact material joined to the distal end side of the bimetal 2, and 43 denotes a contact material joined to the terminal electrode 3, which is set to a predetermined thickness so that the contacts 42 and 43 are always in contact.

According to the present invention, in order to prevent the overcurrent of the battery from being suppressed, the above-mentioned overcurrent protection element is closely fixed to the battery container, and the protection element is connected to the above-mentioned battery protection circuit, and the protection element is turned on.・ If the OFF operation continues for a certain period of time or more, the main control circuit detects this and activates the switching circuit. When the detection circuit detects the non-operation of the switching circuit, the auxiliary control circuit activates the fuse cutoff circuit. On the other hand, when the ON / OFF operation of the protection element is within a predetermined time, the discharge / charge of the battery is normally continued after the predetermined time.

In the above, when an overcurrent flows through the overcurrent protection element, the bimetal 2 generates Joule heat, and the bimetal 2 is bent and deformed as shown in FIG.
2, 43 are turned off. When the contacts are turned off, the energizing current becomes 0, the Joule heating of the bimetal 2 is stopped, the bimetal 2 is cooled, and the contact 42, 43 is turned on as shown in FIG. The ON / OFF of this contact is controlled by the amount of Joule heat generated by the bimetal and the heat dissipation resistance.The amount of Joule heat generated by the bimetal is affected by the resistance and current values of the bimetal, and the heat dissipation resistance is affected by the temperature of the battery container. (The higher the battery container temperature, the more difficult it is to cool the bimetal).

FIG. 2A shows an ideal temperature of the bimetal.
Figure 2 (b) shows the ideal on-off of overcurrent.
State, overcurrent flows and bimetal temperature is normal
Temperature T₀To temperature T₁The contact turns off when
And the bimetal temperature is T₂T until it is reduced to₁
During this period, the contact OFF state is maintained, the current is set to 0, and
The bimetal temperature rises due to the overcurrent flowing when the contacts turn on.
The bimetal temperature is T₁Time t until₂Between
State is maintained, an overcurrent flows, and the next time t ₁Between
Is kept off, the current is set to 0, and
When the on / off of the barrel is repeated, t₁Of the time
0 current, t₂The overcurrent energization over time is repeated.

In FIG. 2B, I ₀ is an overcurrent, I
_x is the average current,

## EQU1 ## I _x = t ₂ I ₀ / (t ₁ + t ₂ ) = I ₀ / (1
+ T ₁ / t ₂ ). The而Ru, as overcurrent I ₀ is large, since the time t ₂ with heating rate of bimetal faster becomes small, as is apparent from the above equation, as the over-current I ₀ is large , the average current _{I x} is reduced. However, in order to prevent heat and explosion of the battery, it is effective to reduce the average current as the overcurrent is large. Therefore, according to the present invention, heat and explosion of the battery can be favorably prevented. In addition, a overcurrent protection device is in close contact with the container of the battery, as the pot temperature of the battery is high, since the bimetal is the faster heated to a temperature T ₁ of the said said time t ₂ is much shorter, average The current is further reduced. Therefore, the overcurrent of the battery can be suppressed in a safer direction, and the explosion can be prevented.

In the above-described embodiment, a bimetal is used for the overcurrent protection device.
Shape memory alloys can also be used. In addition, by generating a control signal from the sensor and the circuit, and operating the relay switch, photocoupler, transistor, FET, etc., the on / off time ratio is changed so that the average current decreases as the overcurrent increases. Is also good.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The protective element shown in FIG. 1 was used. A bimetal was a bimetal having a thickness of 0.2 mm in which a Cu--Ni--Mn alloy piece and a Fe--Ni alloy piece were laminated. A copper plate was used as a contact material, and silver was used as a contact material. The joining between the contact material and the bimetal and the joining between the contact material and the terminal electrode were performed by welding. The protection element, the battery, and the variable load are connected in series and a constant current is passed.
When the off-state was observed, no on-off operation was observed up to 3.5 amps, but on-off operation was obtained at 4.0 amps or more. It was confirmed that the average current at the time of 4.0 ampere was 71%, the average current at the current of 4.5 amps was 49%, and the average current was 5.0 amperes. Average current of 43
%, The average current at a current of 5.5 amps is 33%, the average current at a current of 6.0 amps is 24%, the average current at a current of 6.5 amps is 16%, and the average current is 8.0.
The average current at ampere was 12% and the average current at 9.5 amperes was 7%.

[0014]

In the method for preventing overcurrent of a battery according to the present invention, the overcurrent is suppressed by changing the on / off time ratio so that the average current decreases as the overcurrent increases. Explosion due to overcurrent can be prevented well. Further, since the protection element is operated by reversible thermal expansion / contraction deformation, when the protection element is returned to the normal state as described above, the internal resistance of the protection element is also returned to the original resistance value, and a new wasteful battery is used. There is no burden.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of an overcurrent protection device used in the present invention.

FIG. 2 is a diagram showing an overcurrent ON / OFF state according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation block 2 Bimetal 3 Terminal electrode 42 Contact material 43 Contact material

Claims (3)

[Claims] 1. A method for reducing the average current by turning on / off current when an overcurrent occurs, wherein the on / off time ratio is changed so that the average current decreases as the overcurrent increases. Battery overcurrent prevention method. 2. The method according to claim 1, wherein the on / off of the overcurrent is performed by a bimetal switch. 3. A Cu-Ni-Mn switch for a bimetal switch.
The method for preventing overcurrent of a battery according to claim 2, wherein a bimetal in which an alloy piece and an Fe-Ni alloy piece are laminated is used.