Methods of discharge control for a battery pack of a cordless power tool system, a cordless power tool system and battery pack adapted to provide over-discharge protection and discharge control

Abstract

In a cordless power tool system, a battery pack which may removably attachable to a cordless power tool and to a charger may include at least one battery cell and a power limiting device. The power limiting device may be arranged in series with the at least one battery cell for limiting power output of the battery pack based on the component that is connected to the pack. Current and hence power out of the battery pack may be controlled as a function of total internal impedance in the battery pack, which may be adjusted depending on the component that is connected to the pack.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims domestic priority under 35 U.S.C. §120 to the following related U.S. Provisional patent applications filed in the United States Patent & Trademark Office: U.S. Provisional Application Ser. No. 60 / 507,955, filed Oct. 3, 2003, U.S. Provisional Application Ser. No. 60 / 510,125, filed Oct. 14, 2003, and U.S. Provisional Application Ser. No. 60 / 540,323, filed Feb. 2, 2004. The entire contents of the disclosures for each of these provisional applications are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to methods of discharge control for rechargeable batteries, to a cordless power tool system adapted to provide over-discharge protection and discharge control for an attached battery pack, and to a battery pack including discharge control and over-discharge protection circuits and components. [0004] 2. Description of Related Art [0005] O...

AI Technical Summary

Problems solved by technology

In an over-discharged state, however, the Li-ion batteries deteriorate rapidly, thus Li-ion batteries require over-discharge protection.

However, much higher voltages than described above are required for higher-power electronic devices such as cordless power tools.

However, as this battery technology advances the introduction of lower impedance chemistries (such as lithium-ion chemistry) and construction styles to develop secondary batteries generating substantially higher output voltages then about 4.2 volts / cell may possibly create compatibility issues with existing cordless power tools.

Such undesirable demagnetization could thus potentially burn up the tool motor.

For example, a lower impedance electrical source could cause damage to a tool's motor when the tool is held at stall condition.

Additionally, start-up of the tool could produce excessive starting currents and cause demagnetization of the motor.

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