Battery charger with improved change stopping capability

• US 5,449,996 A
• Filed: 08/17/1993
• Issued: 09/12/1995
• Est. Priority Date: 08/20/1992
• Status: Expired due to Term

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Watanable, Hideki, Matsumoto, Toshio
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TSO, EDWARD H
• Application Number:
  US08/107,120
• Time in Patent Office: 756 Days
• Field of Search: 320/20, 320/30, 320/31, 320/27, 320/48, 320/39, 320/40
• US Class Current: 320/148
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery charger includes a circuit for monitoring a battery voltage during supply of a charging current to a battery, and a circuit for stopping the supply of the charging current when the battery voltage is decreased by a predetermined value after the battery voltage has reached its maximum value. A first predetermined value is adopted as the predetermined value when an increasing tendency of the battery voltage is detected after a predetermined time has elapsed from starting of the charging operation. A second predetermined value is adopted as the predetermined value until the increase tendency of the battery voltage is monitored after the predetermined time has elapsed from starting of the charging operation. The absolute value of the first predetermined value is determined to be smaller than that of the second predetermined value. The predetermined time is determined to be longer than the period of duration of temporary abrupt variation in the battery voltage which may be produced at the beginning of the charging operation of the over-discharged battery.

Claims

1. A battery charger comprising:

means for monitoring a battery voltage during supply of a charging current to a battery; and

means for stopping the supply of the charging current when the battery voltage is decreased by a predetermined value after the battery voltage has reached its maximum value;

said predetermined value being selected from a first predetermined value and a second predetermined value;

said first predetermined value being adopted as said predetermined value when an increasing tendency of the battery voltage is detected after a predetermined time has elapsed from starting of the charging operation;

said second predetermined value being adopted as said predetermined value until the increasing tendency of the battery voltage is detected after the predetermined time has elapsed from starting of the charging operation;

an absolute value of said first predetermined value being smaller than an absolute value of said second predetermined value; and

said predetermined time being determined to be longer than a period of duration of temporary abrupt variation in the battery voltage which may be produced at beginning of the charging operation of an over-discharged battery.

2. The battery charger as defined in claim 1, further comprising:

means for temporarily storing the monitored battery voltage and for monitoring the charging current; and

means for incorporating, in place of the battery voltage produced at that time when the charging current is out of a predetermined range, the battery voltage produced just before that time and produced when the charging current is within said predetermined range.

3. The battery charger as defined in claim 1, further comprising:

means for monitoring variation in the battery voltage at intervals of a second predetermined time;

means for extracting and storing a maximum variation from the monitored variation; and

means for stopping the supply of the charging current when the monitored variation has become less than a value of subtraction of a third predetermined value from the maximum variation.