Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2000-02-28
2001-03-20
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06204639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery charger for charging batteries that are used as the power source of a portable device, such as a cordless power tool. Examples of batteries include nickel cadmium batteries, and nickel hydrogen batteries
2. Description of the Related Art
Recently, nickel cadmium batteries, nickel hydrogen batteries, and other secondary batteries are being produced with a large capacity and improved charge characteristic when charged with a large current.
The cycle life of a battery can be reduced if the battery is allowed to overheat during charge. To prevent this potential reduction in cycle life, battery chargers stop charging operations, once the subject battery has heated up to a predetermined temperature, of 60° C. for example. However, large capacity batteries generate more heat when charged than do batteries with a smaller rated capacity. When large rated capacity batteries are charged using the same large charge current as used for charging small rated capacity batteries, then large rated capacity batteries heat up and exceed the predetermined temperature before being fully charged. Because the charging operations are stopped at this point, the battery is less than fully charged.
For this reason, a battery charger has been proposed that charges small rated capacity batteries using a relatively large charge current and charges large rated capacity batteries using a relatively small charge current. However, such a battery charger takes a long time to charge large rated capacity batteries.
Another charger is provided with cooling device, such as a cooling fan, for cooling down the battery while it is being charge. With this configuration, even large rated capacity batteries can be quickly charged using a relatively large charge current without damaging the battery. However, this type of battery charger is, as a matter of course, more expensive than battery chargers without cooling device, and so is unappealing to users that only rarely need to charge large rated capacity batteries. Further, battery chargers without cooling device are quite capable of properly charging large rated capacity batteries, although they require longer to do so. Therefore, there is no absolute necessity for battery chargers to have cooling device. For such reasons, both battery chargers with cooling device and battery chargers without cooling device are present on the market. This requires a manufacturer or retailer to provide various support, such as repair and maintenance support, for both battery chargers with cooling device and battery chargers without cooling device. Also, producing both types is not very economical, and productivity is poor.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above-described problems, and enable producing both types of battery charger using a common control circuit board, thus providing an inexpensive and economic battery charger with excellent productivity.
The present invention achieves the above-described objectives by detecting whether a battery charger includes cooling device, and changing the charging current in accordance with the detection results.
In accordance with the present invention, there is provided a battery charger including a microcomputer, a charge current supplying section for supplying a charge current to a battery pack to be charged, a connector to which a cooling device is optionally connectable, a cooling device detection circuit, and a charge current control section. The cooling device detection circuit is operatively connected to the microcomputer and the connector and detects whether or not the cooling device is connected to the connector. The cooling device detection circuit outputs a first signal to the microcomputer when the cooling device is connected to the connector and a second signal to the microcomputer when the cooling device is not connected to the connector. The charge current control section is operatively connected to the microcomputer and the charge current supplying section. The microcomputer instructs the charge current control section to control an average charge current to be applied to the battery pack during charging of the battery pack in response to outputs from the cooling device detection circuit.
Further, a battery type distinction circuit is operatively connected to the microcomputer and the battery pack for identifying types of the battery packs classified in terms of rated capacity, e.g., whether the battery pack is of a large rated capacity or a small rated capacity. The battery type distinction circuit outputs a type indication signal to the microcomputer. Then, the microcomputer instructs the charge current control section to control the average charge current in further response to the type indication signal.
Specifically, the microcomputer instructs the charge current control section to use a first charge current in response to the first signal and to use a second charge current in response to the second signal and when the type indication signal indicates that the battery pack is of a large rated capacity. In this case, the first charge current has an average level larger than an average level of the second charge current. In the case where the cooling device is not detected, the small rated capacity battery packs may not necessarily be charged with the first charge current but be charged with a third charge current that has an average level between the levels of the first charge current and the second charge current. However, the microcomputer may instruct the charge current control section to use the first charge current in response to the second signal and when the type indication signal indicates that the battery pack is of a small rated capacity.
It is preferable to have a battery temperature detection circuit that is operatively connected to the microcomputer for detecting a temperature of battery cells contained in the battery pack. The battery temperature detection circuit outputs a temperature signal indicative of the temperature of the battery cells to the microcomputer. Then, the microcomputer instructs the current setting circuit to decrease the average charge current when the microcomputer determines that a battery temperature gradient per a unit time is greater than a predetermined value at the time of start of the charging operation.
The microcomputer instructs the current setting circuit to maintain the average charge current when the battery temperature gradient per the unit time is greater than the predetermined value at the time of start of the charging operation and when the type indication signal indicates that the battery pack is of a small rated capacity.
Further, the microcomputer instructs the current setting circuit to decrease the average charge current when the microcomputer determines that a battery temperature gradient per a unit time is greater than a predetermined value at the time of start of the charging operation and when the type indication signal indicates that the battery pack is of a large rated capacity.
The present invention as configured above is applicable to battery chargers for charging battery packs with and without a cooling device.
REFERENCES:
patent: 4229687 (1980-10-01), Newman
patent: 5606239 (1997-02-01), Schumann
patent: 0 920 105 (1999-06-01), None
patent: 0 940 864 (1999-09-01), None
patent: 11-339861 (1999-12-01), None
Iimura Yoshio
Ishimaru Kenrou
Shima Yukihiro
Takano Nobuhiro
Hitachi Koki Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tso Edward H.
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