Battery charger and charging method

• US 6,204,641 B1
• Filed: 03/20/2000
• Issued: 03/20/2001
• Est. Priority Date: 02/28/1998
• Status: Expired due to Term

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Sakakibara, Kazuyuki
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/531,596
• Time in Patent Office: 365 Days
• Field of Search: 320/150, 320/153
• US Class Current: 320/153
• CPC Class Codes: H02J 7/007194 of the battery

Abstract

A battery charger and a charging method capable of charging a battery for a short period of time while suppressing the battery temperature from rising, by incorporating in the battery charger memory a look-up table for mapping an allowable value of current with which the battery can be charged based on a battery temperature and a battery temperature rise only. The current temperature of the battery is detected (in step S12) and a temperature rise is calculated from the detected temperature (in step S14). An allowable current map is then retrieved from the detected temperature and the obtained temperature rise, an allowable current with which the battery can be charged while suppressing battery temperature from rising is obtained (in step S16) and the battery is charged with the allowable current (in step S20). Since the allowable current which the battery can be charged with, while suppressing battery temperature from rising is retrieved using the map which the allowable current is mapped, based on battery temperature and battery temperature rise, and charging current is controlled, it is possible to charge the battery for a short period of time while suppressing battery temperature from rising.

Claims

1. A battery charger comprising:

a memory for storing a map for mapping an allowable value of current, with which a battery can be charged while suppressing battery temperature from rising, based only on a battery temperature and a battery temperature rise;

a temperature detection device for detecting a current temperature of the battery;

a temperature rise output device for obtaining the temperature rise from the temperature detected by said temperature detection device;

an allowable current retrieval device for retrieving the map of said memory device from the temperature detected by said temperature detection device and the temperature rise outputted from said temperature rise output device, and for obtaining said allowable value; and

a charging device for charging the battery with the allowable current retrieved by said allowable current retrieval device.

2. The battery charger according to claim 1, wherein said allowable current retrieval device determines, after said charging device starts charging the battery, if the obtained current value is within a predetermined portion of the map representing predetermined levels of temperature rise, and said charging device continues charging the battery until the current value is within the predetermined portion.

3. The battery charger according to claim 2, wherein said predetermined levels are middle and high levels of temperature rise.

4. A charging method comprising:

detecting current temperature of a battery;

obtaining a temperature rise from said detected temperature;

retrieving an allowable current map based only on battery temperature and battery temperature rise, from said detected temperature and said obtained temperature rise, and obtaining an allowable value of current, with which the battery can be charged while suppressing the battery temperature from rising; and

charging the battery with said retrieved allowable current.

5. The charging method according to claim 4, wherein after starting to charge the battery, determining if said allowable current is within a predetermined portion of the map representing predetermined levels of temperature rise, and continuing charging the battery until the current value is within the predetermined portion.

6. The charging method according to claim 5, wherein said predetermined levels are middle and high levels of temperature rise.