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Control method and control apparatus for secondary battery charging in constant current charging method
| Details |
Inventors: Takeda, Yoshiro;
Assignee: Fujitsu Limited (Kawasaki, JP)
Primary Examiner: Tso; Edward H.
Assistant Examiner:
Attorney, Agent or Firm: Staas & Halsey
A method for controlling a secondary battery constant current charging method and a control apparatus therefor, which measures battery voltage (V), a change in battery voltage per unit time (.DELTA.V/.DELTA.t), a decrease in battery voltage (-.DELTA.V) from a maximum value, battery temperature (T), and/or a change in battery temperature per unit time (.DELTA.T/.DELTA.t); and stops the battery charging when .DELTA.V/.DELTA.t is greater than or equal to a predetermined value after the passage of a predetermined time t.sub.S, or when .DELTA.V/.DELTA.t and .DELTA.T/.DELTA.t are greater than or equal to predetermined values, or when .DELTA.V/.DELTA.t and T are greater than or equal to predetermined values, or when V is greater than or equal to a maximum value V.sub.P, or when either the -.DELTA.V or T is greater than or equal to a predetermined value. |
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DETAILED DESCRIPTION Therefore, the present invention has as its object the provision of a control method and a control apparatus for charging a battery, which can prevent the battery from being overcharged thus increasing battery life, and which can prevent an erroneous detection of the battery charging being completed before the battery charging is actually completed.
To achieve the above-mentioned object, in a first aspect of the present invention, in the constant current charging method for a secondary battery, a charge in battery voltage per unit time .
DELTA.
V/.
DELTA.
t is measured after the passage of a predetermined time t.
sub.
S from the start of the battery charging.
When the value of .
DELTA.
V/.
DELTA.
t is over a predetermined value .
DELTA.
V.
sub.
X1, it is judged that the battery is completely charged, and the battery charging is stopped.
In this aspect of the invention, since the value of .
DELTA.
V/.
DELTA.
t is not measured when the battery charging is started, a possible error in judging the .
DELTA.
V/.
DELTA.
t at the start of the battery charging as an indication of the completion of the battery charging is prevented.
Therefore, the battery charging can be stopped just before the battery is completely charged, and the battery life can be extended.
In a second aspect of the present invention, in the constant current charging method for a secondary battery, the value of .
DELTA.
V/.
DELTA.
t and the increased battery temperature value per unit time .
DELTA.
T/.
DELTA.
t are measured during the battery charging period.
When both values .
DELTA.
V/.
DELTA.
t and .
DELTA.
T/.
DELTA.
t are greater than or equal to respectively predetermined values .
DELTA.
V.
sub.
X1, .
DELTA.
T.
sub.
X1, it is judged that the battery is completely charged, and the battery charging is stopped.
In this aspect of the invention, an error in judging the completion of the battery charging due to a change in the ambient temperature or a change in the voltage over time at the start of battery charging can be prevented.
In the third aspect of the present invention, in the constant current charging method for a secondary battery, the value of
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