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.

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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.