United States Patent
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`[:9]
`
`Lee
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`USOOSZOOGBGA
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`[11]
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`[45]
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`Patent Number:
`
`Date of Patent:
`
`5,200,686
`
`Apr.6,1993
`
`METHOD AND APPARATUS FOR
`DETERMINING BATTERY TYPE
`Inventor:
`
`Steven S. Lee, Northbrook, 11].
`
`Motorola, Inc., Schaumburg, Ill.
`Assignee:
`Appl. No.: 774,435
`Filed:
`Oct. 10, 1991
`
`Int. Cl.5 ...................... .. I-l02J 7/00; HOIM 10/44
`US. Cl. ........................................ .. 320/2; 320/15;
`429/7
`Field of Search ................. 320/2, 15; 455/89. 90;
`429/7
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,659,180 4/1972 Urbush .................................... 320/2
`4,006,396 2/1977 Bogut ...................................... 320/2
`
`4,593,409 6/1986 Miller .............................. .. 320/48 X
`4,670,703
`6/1987 Williams .......
`.. 320/15 X
`4,680,527 7/1987 Benenati ct al. ........................ 320/2
`
`Primary Examiner——R. J. Hickey
`Attorney, Agent, or Firm——John W. Hayes
`
`[57]
`
`ABSTRACT
`
`Battery type is determined by measuring effective resis-
`tance of a thermistor/resistor network (205, 206, and
`207) and one or_more of a plurality of current sources
`(303-305) is enabled to provide the appropriate charg-
`ing current. Measurement of necessary charging param-
`eters and provision of appropriate charging current are
`accomplished through an interface to the battery pack
`undergoing charge that comprises only three connec-
`tions (313-315).
`
`6 Claims, 1 Drawing Sheet
`
`AMX
`Exhibit 1018-00001
`
`

`
`Apr. 6, 1993
`
`5,200,686
`
`FICJ
`
`—-PRIOR ART—-
`
`'
`
`101
`
`I I I
`
`702
`
`103
`
`104
`
`200
`
`F[C.2 2 01
`
`LOW CAPACITY
`CURRENT
`SOURCE
`
`307
`
`*MICROCOMPUTER
`
`302
`
`A/D
`CONVERTER
`
`308
`
`AMX
`Exhibit 1018-00002
`
`

`
`1
`
`5,200,686
`
`METHOD AND APPARATUS FOR DETERMINING
`BATTERY TYPE
`
`TECHNICAL FIELD
`
`This invention relates generally to battery powered
`equipment and in particular to battery chargers, and is
`more particularly directed toward a method and appa-
`ratus for distinguishing between different types of bat-
`teries.
`
`‘
`
`BACKGROUND OF THE INVENTION
`Since the advent of two-way radio communication,
`designers have been faced with the challenge of making
`radio equipment smaller and smaller. The ultimate goal
`has been to reduce equipment size to the point where it
`is easy for an individual user to carry and operate it.
`Any unit intended to be carried by an individual is
`usually designated as portable, and communication
`units designed for extremely small size and ease of use
`are often termed “personal” communication units.
`Of course, units designed for the individual user are
`generally equipped with batteries, since it is assumed
`that it would be inconvenient to require the user to
`search for a power source before commencing commu-
`nication. Indeed, it is the “ready-to-use” nature of por-
`table equipment that constitutes perhaps its greatest
`appeal.
`Naturally, an associated integral battery may add
`\ undesired size and weight to portable equipment. But,
`since battery size and battery capacity are generally
`directly proportional to one another, frequent users are
`more tolerant of increased battery size and weight be-
`cause these users need more “talk time" and “standby
`time” than infrequent users. The term “talk time,” when
`applied to portable communication units, generally
`refers to battery life measured while the transmitter
`portion of the communication unit is active. “Standby
`time" refers to battery life measured while the commu-
`nication unit is in a powered-on state, but with the trans-
`mitter inactive.
`
`Still, the majority of portable equipment users, and
`not a small number of frequent users, stress the small
`size and weight aspects of portable equipment when
`making a purchase decision. Thus, considerable pres-
`sure still exists on designers to make even highcapacity
`battery assemblies as compact as possible.
`Most battery assemblies intended for portable use are
`designed to be rechargeable to maximize user conve-
`nience. It is much more economical to place a battery
`assembly (or battery pack, as it is sometimes called) into
`a charger for a period of time than to be compelled to
`purchase new batteries every time battery voltage drops
`below a useful level. Extant rechargeable battery packs
`generally include four contacts disposed on a conve-
`nient exterior surface for compatibility with a battery
`charger. These contacts permit electrical access to com-
`ponents that help to determine, among other things, the
`desired charge rate for a given battery pack and when
`the battery is adequately charged. This contact arrange-
`ment is an important factor in determining how small a
`battery pack can be, since exterior surface area must be
`maintained to accommodate the external contact array.
`Accordingly, a need arises for a method for effec-
`tively reducing the number of contacts required so that
`a corresponding reduction may be effected in battery
`size, weight, cost, and complexity. Of course,
`this
`
`2
`contact reduction must not affect the ability to measure
`critical battery charging parameters.
`SUMMARY OF THE INVENTION
`
`This need and others are satisfied by the method of
`the present invention for determining battery type and
`adjusting charging parameters accordingly for a battery
`charger system having only three terminals for inter-
`connection between a battery charger and a battery
`pack to be charged. First, the effective resistance of a
`thermistor/resistor network connected between two of
`the terminals is measured to determine battery type,
`then one or more of a plurality of current sources, cou-
`pled to a third terminal, are_ enabled to provide an ap-
`propriate charging current.
`In one embodiment, the measurement of efiective
`resistance is accomplished by measuring voltage at one
`terminal, with a fixed resistance connected between that
`terminal and a relatively constant voltage. An analog-
`to-digital converter (ADC) is used to make this voltage
`measurement, and a microcomputer controls the selec-
`tion of the appropriate current source or sources. In the
`preferred embodiment, the ADC is included within the
`microcomputer.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 depicts a battery pack of the prior art;
`FIG. 2 illustrates a battery pack constructed to oper-
`ate in the battery charger system of the present inven-
`tion; and
`FIG. 3 is a block diagram of a battery charger that
`may be used to implement the method of the present
`invention.
`
`DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`A battery pack of the prior art is illustrated in FIG. 1,
`generally depicted by the numeral 100. The battery
`pack is provided with four relatively closely-spaced
`contacts (102-105) disposed on an exterior surface of
`the battery pack housing (101). One contact (105) is
`coupled to an array of rechargeable battery cells (108),
`generally of nickel cadmium construction, although
`other materials may also be used. The battery cells (108)
`are also coupled to a common contact (103).
`An internal resistor (107) is shown coupled between a
`dedicated resistor contact
`(104) and the common
`contact (103). The value of this internal resistor (107) is
`measured by external charging equipment to determine
`battery type and associated charging rate. In general, a
`particular manufacturer will assign specific resistor
`values to specific battery types in order to ensure com-
`patibility between that manufacturer’s batteries and its
`charging equipment.
`A thermistor (106) is connected between a dedicated
`contact (102) and the common contact (103). As is well-
`known in the art, a thermistor is a resistor whose value
`varies in a predictable fashion in response to tempera-
`ture. Since the thermistor (106) is placed in close prox-
`imity to the rechargeable battery cells (108), thermistor
`resistance represents an accurate measure of battery cell
`temperature.
`Cell temperature is an important parameter in the
`battery charging art. As is well-known, a nickel cad-
`mium battery is commonly charged by supplying a
`known current to the battery. For rapid charging, a
`relatively large current is supplied, which causes cell
`temperature to increase. In one method of charging
`
`AMX
`Exhibit 1018-00003
`
`

`
`5,200,686
`
`3
`control, called the temperature cut-off method, when
`the cells reach a predetermined temperature the charg-
`ing mode is changed from rapid charge to trickle
`charge. From a practical standpoint, this means that the
`relatively large current used for rapid charging is re-
`duced to a relatively small current. For example, a high
`capacity battery of 1200 milliampere-hour (mAh) ca-
`pacity would commonly be rapid charged with a cur-
`rent of 1200 milliamperes (mA). When the cells reach
`their predetermined temperature, the current is reduced
`to only 80 mA for trickle charging mode.
`A more effective charging control protocol is the
`delta T method. Delta T refers to the fact that the rate
`of change of temperature is measured to determine
`optimum charging of a cell, as opposed to measuring a
`limit temperature as in the temperature cut-off method.
`Of course, in order to implement the delta T technique,
`the battery charger requires a greater degree of sophisti-
`cation.
`The parameters mentioned above (i.e., cell tempera-
`ture and battery type) are required to properly recharge
`a nickel cadmium cell. Through the present invention,
`these parameters can still be measured properly with
`only three interconnections between a battery pack and
`associated charger, thus allowing a smaller battery pack
`to be constructed.
`FIG. 2 illustrates a battery pack, generally depicted
`by the numeral 200, designed for use in the battery
`charging system of the present invention. The battery
`pack (200) includes first, second, and third contacts
`(202, 203, and 204, respectively) disposed upon an exte-
`rior surface (201). An arrangement of one or more re-
`chargeable cells (208) is provided between the first and
`second contacts (202 and 203). A thermistor (205) and a
`first resistor (206), are connected in parallel, with one
`end of the parallel combination coupled to the second
`contact (203). The other end of the parallel combination
`is coupled to the third contact (204) through a second
`resistor (207). The second contact (203) serves as a
`common contact, and would generally be connected to
`ground potential during recharging operations.
`The battery pack of FIG. 2 operates in conjunction
`with the battery charger shown in block diagram form
`in FIG. 3, and generally depicted by the number 300. In
`order to make proper contact with a battery pack to be
`charged, a battery charger is normally equipped with a
`pocket (316). This pocket is generally nothing more
`than a depression in the battery charger housing in
`which contacts (313-315) arranged to mate with corre-
`sponding battery pack contacts are disposed. The
`pocket is nonnally designed to accommodate a portable
`communication unit with battery attached, although
`many configurations are possible. Some chargers will
`accept a battery pack alone, without the associated
`portable equipment, and various physical orientations
`of the unit undergoing charging, such as upright, hori-
`zontal, or inclined, are contemplated in battery charger
`designs known in the art. The contacts shown in FIG. 3
`are designed to mate with the contacts of FIG. 2 such
`that the first contact (202) of the battery pack (200) 60
`connects to the first contact (313) of the battery charger
`(300), the second contact (203) of the battery pack (200)
`connects to the second contact (314) of the battery
`charger (300), and the third contact (204) of the battery
`pack (200) connects to the third contact (315) of the 65
`charger (300).
`A plurality of current sources (303-305) can be selec-
`tively enabled to provide proper charging current in a
`
`4
`manner to be discussed in more detail below. A current
`source can be constructed using discrete transistors and
`resistors by anyone having ordinary skill in the art.
`Determination of battery type, as described in a pre-
`5 ceding section, is ordinarily accomplished by measuring
`the value of a resistor internal to the battery pack being
`charged. Another way to determine resistance is to
`place the unknown resistance in a voltage divider net-
`work with one or more known resistances to which a
`known voltage is applied. This technique is used in the
`preferred embodiment of the invention through the use
`of a known resistance value (310) coupled to a known
`supply voltage (311). An analog-to-digital converter
`(302) is coupled (309) to the first contact (315) of the
`pocket (316) to measure the voltage across the thermis-
`tor/resistor network (205-207) described with refer-
`ence to FIG. 2 above.
`Judicious selection of resistor values permits battery
`type to be accurately determined despite resistance
`fluctuations caused by the temperature dependence of
`the thermistor’s resistance. Since the values of the fixed
`resistors (206 and 207) in the network are known, varia-
`tions in resistance can be accurately associated with cell
`temperature. Of course, computation of resistor value
`and cell temperature parameters is relatively simple in
`the preferred embodiment, since computation and con-
`trol are performed by a microcomputer (301). Prefera-
`bly, the microcomputer is an MC6805R2 microcom-
`puter manufactured by Motorola, Inc. The microcom-
`puter
`(301)
`includes an analog-to-digital converter
`(ADC) (302) and can be easily programmed by one of
`ordinary skill in the pertinent art to perform measure-
`merit, calculation, and control functions. Initial battery
`voltage can also be measured by the ADC (302)
`through a dedicated input (317) for determination of
`initial cell charge state. If a cell is not discharged, appli-
`cation of full rapid charge current would be inappropri-
`ate.
`Resistance values and corresponding battery types
`are stored in microcomputer (301) memory. When the
`battery type has been identified, the microcomputer
`(301) enables, through control signal outputs (307 and
`. 308), appropriate current sources (307 and 308) to im-
`plement the indicated charging mode. The low capacity
`current source (303) is always enabled, since its small
`current output has little impact on the rapid charge
`current for a given battery type. For a battery identified
`as a high capacity battery, the microcornputerwould
`enable both high capacity current sources (304 and 305)
`to provide the relatively high current required to rapid
`charge a high capacity battery. For a battery identified
`as lower capacity, only one of the current sources (304)
`would be enabled, since rapid charging a lower capac-
`ity battery requires Iess current. In the preferred em-
`bodiment, two battery types are possible. For the high
`capacity battery, rated at 1200 mAh, both current
`sources (304 and 305) are enabled. Each current source
`provides a current of 600 mA, yielding a total current of
`1200 mA. The lower capacity battery, rated at 600
`mAh, requires only one current source (304) during
`rapid charge mode. For either battery type, once the
`battery is charged, the high capacity current sources are
`disabled by the microcomputer (301) leaving only the
`low capacity current source (303) to provide a current
`of 80 mA for trickle charge mode.
`What is claimed is:
`1. A battery charger apparatus comprising:
`
`AMX
`Exhibit 1018-00004
`
`

`
`5,200,686
`
`5
`a battery pack having first, second, and third contacts
`disposed upon an exterior surface, the battery pack
`including:
`i
`one or more rechargeable cells arranged between
`the first and second contacts;
`a thermistor and a first resistor in parallel combina-
`'tion, with one end of the combination connected
`to the second contact;
`a second resistor connected between the other end
`of the combination and the third contact;
`a battery charger including:
`a pocket having first, second, and third contacts,
`the pocket constructed and arranged so that the
`first, second, and third contacts of the pocket
`operably engage the first, second, and third
`contacts, respectively, of the battery pack;
`a plurality of current sources that may be enabled
`individually or
`in combination,
`the current
`sources coupled to the first contact of the
`pocket;
`
`6
`means for measuring voltage coupled to the third
`contact of the pocket;
`controller means, coupled to the plurality of cur-
`rent sources and to the means for measuring
`voltage, for selectively enabling one or more of
`the current sources in response to the measured
`voltage.
`2. The apparatus of claim 1, wherein the means for
`measuring voltage comprises an analog-to-digital con-
`verter.
`
`3. The apparatus of claim 1, wherein the controller
`means comprises a microcomputer.
`4. The apparatus of claim 3, wherein the microcom-
`puter includes an analog-to-digital converter.
`5. The apparatus of claim 1, wherein the plurality of
`current sources includes a current source of relatively
`small capacity applicable to trickle charging.
`6. The apparatus of claim 1, wherein the plurality of
`current sources includes at least two current sources of
`relatively high capacity that may be selectively enabled,
`either individually or together, to provide rapid charge
`capability for batteries of different types.
`I
`I
`3
`8
`I
`
`AMX
`Exhibit 1018-00005