Battery charging method

• US 20050127873A1
• Filed: 12/09/2004
• Published: 06/16/2005
• Est. Priority Date: 12/11/2003
• Status: Active Grant

• Current Assignee: Panasonic Energy Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamamoto, Hiroyoshi, Yamaguchi, Masao, Tamai, Mikitaka
• Granted Patent: US 7,408,325 B2
• Time in Patent Office: Days
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

The battery charging method detects the voltage of each series connected battery, discharges batteries with voltage exceeding a prescribed voltage, and charges a plurality of batteries while maintaining cell balance. This charging method detects the voltage of each battery being charged and if any battery voltage exceeds the prescribed voltage, only the battery that exceeds the prescribed voltage is discharged, after a specified charging time, until its voltage drops to the prescribed voltage. Batteries that do not exceed the prescribed voltage are not discharged, and thereby all batteries are charged while balancing their voltages.

Claims

1. A battery charging method which charges a plurality of rechargeable batteries connected in series, detects the voltage of each battery, discharges batteries that exceed a prescribed voltage, and charges while maintaining cell balance;

and characterized in that the voltage of each battery is detectable, if the voltage of any battery exceeds the prescribed voltage, charging is performed for a specified charging time, subsequently only the battery that exceeds the prescribed voltage is discharged until its voltage drops to the prescribed voltage without discharging batteries that do not exceed the prescribed voltage, and thereby charging while balancing battery voltages.

2. A battery charging method as recited in claim 1 wherein charging of all batteries is suspended while the battery that exceeds the prescribed voltage is discharged.

3. A battery charging method as recited in claim 1 wherein if the voltage of any battery still exceeds the prescribed voltage even after a delay time has elapsed, charging is performed for a specified charging time, subsequently only the battery that exceeds the prescribed voltage is discharged until its voltage drops to the prescribed voltage without discharging batteries that do not exceed the prescribed voltage, and thereby charging while balancing battery voltages.

4. A battery charging method as recited in claim 3 wherein charging of all batteries is suspended while the battery that exceeds the prescribed voltage is discharged.

5. A battery charging method as recited in claim 1 wherein the batteries are lithium ion batteries.

6. A battery charging method as recited in claim 1 wherein discharge circuitry comprising a series connected discharge resistor and switching device is connected in parallel with each battery;

when the voltage of any battery exceeds the prescribed voltage, the discharge circuit switching connected in parallel with that battery is turned ON, and part of the charging current is bypassed through the discharge resistor.

7. A battery charging method as recited in claim 6 wherein discharge current for a discharge circuit switching device, which is turned ON, is less than the changing current;

a battery that exceeds the prescribed voltage is charged with less current than batteries that do not exceed the prescribed voltage for the specified charging time; and

subsequently only the battery exceeds the prescribed voltage is discharged until it drops to the prescribed voltage without discharging batteries that do not exceed the prescribed voltage.