Low power indication circuit for lead acid battery pack

Details Low power indication circuit for lead acid battery pack Low power indication circuit for lead acid battery pack

2000-05-24

2001-11-06

Wong, Peter S. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

Regulated discharging

C320S132000, C320S162000

Reexamination Certificate

active

06313611

ABSTRACT:

BACKGROUND
The present application relates to battery packs of the type usable with cordless power tools and, in particular, to lead-acid battery packs. The application relates in particular to techniques for protecting against deep discharge of lead-acid battery packs.
Cordless power tools commonly use a NiCad battery pack to power an electric motor. Such tools are commonly used until the battery pack is completely discharged, since NiCad cells can tolerate deep discharges and, in some circumstances, are actually revived by deep discharge/charge cycling. Furthermore, the discharge of a NiCad battery is apparent to the user, since, as the battery approaches deep discharge, the power deliverable by the tool is reduced until, eventually, the tool will stop working.
It is also known to utilize lead-acid batteries in various devices because such batteries afford certain power delivery advantages. Such lead-acid batteries, of a size suitable for use in cordless power tool battery packs, are sold by Bolder Technologies under the designation “Bolder 9/5 sub-C TMF” (Thin Metal Film). However, unlike NiCad batteries, lead-acid batteries do not tolerate deep discharges. Discharge of lead-acid batteries below about 50% state-of-charge adversely affects battery life and could cause permanent damage. Thus, to ensure maximum battery life, such batteries should not be discharged below about 50% state-of-charge. Furthermore, when such lead-acid batteries are utilized in battery packs for cordless power tools, the discharge of the battery to about 50% state-of-charge may not be readily apparent to the user, since the battery can still deliver substantial power at such state-of-charge levels. Thus, the user may easily discharge the battery to below 50% state-of-charge without knowing that he is doing so.
SUMMARY
There is disclosed below an improved battery pack circuit usable with lead-acid batteries, which avoids the disadvantages of prior battery pack circuits while affording additional structural and operating advantages.
An important feature is the provision of a control apparatus for a device powered by a battery pack, which prevents use of the device when the battery of a battery pack is discharged below a predetermined state-of-charge level.
Another feature is the provision of an apparatus of the type set forth, which applies a gradual reduction of output power when the state-of-charge of the battery of a battery pack drops below a predetermined level.
Another feature is the provision of an apparatus of the type set forth which provides a clear indication to a user of the device when the state-of-charge of the battery of a battery pack drops below a predetermined level.
In connection with the foregoing features, another feature is the provision of an apparatus of the type set forth, which provides indication and/or shutdown functions when the state-of-charge of the battery of a battery pack remains below a predetermined level for a predetermined time period.
Another feature is the provision of a deep discharge protection circuit for a lead-acid battery pack.
In connection with the foregoing feature, another feature is the provision of a deep discharge protection circuit of the type set forth which simulates the function and feel of a discharged NiCad battery.


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