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Kizu, Masanobu; Nagai, Ryo; Ohshima, Toshio; Ohiwa, Tsunemi; Kajita, Kozo; |
Method of charging secondary batteries

In a method of charging secondary battery, the charging control is performed when it is detected that the secondary differential value of the detected voltage curve changes from positive value to a negative value at the point C or its near portion.


What is claimed is:
1. A method of charging an electrical battery, comprising the steps of:
(a) setting an initial current value of charging current;
(b) detecting the battery voltage at the beginning and end of a plurality of charging time intervals;
(c) determining a first voltage value of the difference in the battery voltage at the beginning and end of successive charging time intervals;
(d) determining a second voltage value of the difference between two successive first voltage values; and
(e) reducing the value of charging current from said initial current value to a lesser current value when said second voltage value thereafter changes from a positive value to a negative value.
2. The method of claim 1 wherein said step (e) of reducing comprises reducing the value of charging current to said lesser current value when said second voltage value thereafter changes from a positive value to a negative value for at least two successive time intervals.
3. The method of claim 1, and additionally including the step of:
(f) reducing the current value of charging current from said lesser current value to a still lesser current value when said first voltage value thereafter goes to a zero value or a negative value.
4. The method of claim 3 and additionally including the step of:
(f) determining when said first voltage value reaches a maximum negative value for indicating a full charge condition of said battery.
5. The method of claim 3 and additionally including the step of:
(f) determining when said second voltage value thereafter changes to a positive value for indicating a full charge condition of said battery.
6. The method of claim 3 and additionally includes the step of:
(f) determining when said first voltage value reaches a maximum negative value or said second voltage value changes to a positive value; and
(g) terminating charging of said electrical battery.
7. The method of claim 1 and additionally including the step of:
(f) waiting for a predetermined time interval prior to initially performing steps (b) through (e).
8. A method of charging an electrical battery, comprising the steps of:
(a) setting an initial current value of charging current;
(b) detecting the battery voltage at the beginning and end of at least two successive charging time intervals;
(c) determining a first voltage value of the difference in the battery voltage at the beginning and of said successive charging time intervals;
(d) determining a second voltage value of the difference between two successive first voltage values;
(e) reducing the value of charging current to a first lower current value when said second voltage value thereafter changes from a positive value to a negative value;
(f) reducing the value of charging current to a second lower current value when said first voltage value thereafter goes to a zero value or a negative value; and
(g) determining when said first voltage value reaches a maximum negative value or said second voltage value goes to a positive value for indicating a full charge condition of said battery.
9. The method of claim 8 and additionally including the step of:
(h) terminating the charging of said battery.
10. The method of claim 8 and additionally including the step of:
(h) delaying steps (a)-(g) for a predetermined initial time interval.
11. The method of claim 8 wherein said first lower current value is greater than said second lower current value.
12. The method of claim 11 wherein said second lower current value comprises a trickle current value.
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