Abstract:
A method for determining time to completion is provided for a battery charging system. The system preferably includes a charger having a microprocessor and a battery with a memory. The memory includes information about the battery, including battery identifiers, charging states, charging procedures and charging termination information. The charger reads this battery and then determines the charging states associated with the battery. The charger then determines the present state of charge, and calculates a time to completion for that state. The charger then determines times to completion for the remaining charge states, optionally compensating for self discharge within the battery. A total time to completion is determined by summing the times to completion for the respective charging states.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     This invention relates generally to fuel gauging for rechargeable battery packs, and more specifically to a method for estimating the time remaining until a rechargeable battery pack is fully charged.  
         [0003]     2. Background Art  
         [0004]     Many portable electronic devices, like cellular telephones, laptop computers, pagers, radios and personal digital assistants (PDAs), rely upon rechargeable batteries for their portability. These batteries provide energy while on the go, but must be recharged once the energy is depleted.  
         [0005]     Some electronic devices include fuel gauging circuits that attempt to display the amount of energy stored within the battery. For example, some devices include a display with a little picture of a battery on the screen. As the rechargeable battery stores energy, the battery picture slowly changes from transparent to colored. By looking at the amount of the battery picture that is colored, a user may roughly estimate how much energy is stored within the battery.  
         [0006]     The problem with these systems occurs during charging. By looking at a graphical fuel gauge, a user can not tell how much longer it will be before the battery is fully charged. Imagine a police officer who wants to take a fully charged radio out on the beat. If he looks at a graphical fuel gauge and sees that his battery is roughly three-quarters charged, what does this tell him about how much longer will it be before the battery is fully charged? Will it be another 20 minutes? 30 minutes? The answer is that he can not tell based upon presently stored energy alone.  
         [0007]     There is thus a need for an improved fuel gauge that tells a user how much time is remaining until a rechargeable battery is fully charged. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  illustrates a preferred method for estimating time to completion in accordance with the invention.  
         [0009]      FIG. 2  illustrates a preferred method for estimating time to completion in accordance with the invention.  
         [0010]      FIG. 3  illustrates an exemplary apparatus for employing the methods of  FIGS. 1 and 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” 
         [0012]     A method of determining the time until completion for a rechargeable battery is provided. “Time to completion” refers to the amount of time remaining until a rechargeable battery is fully charged. For example, if a 25% charged battery were connected to a charger, and it would take 60 minutes until the battery reached 100% charge, the time to completion would be 60 minutes. The method offers distinct advantage in that a person who may be leaving on a long trip our outing will know exactly when the battery will be fully charged so as to better plan his departure time.  
         [0013]     Referring first to  FIG. 3 , illustrated therein is a schematic block diagram of one preferred hardware architecture upon which the method may be implemented in accordance with the invention. The system  300  includes a charger  301  having a power supply  314  and a current regulator  313 . Any number of charging circuits known in the art, including buck regulators, linear regulators, flyback regulators, boost regulators, or equivalent may suffice as the current regulator  313 . The charger  301  may optionally include indicators, like light emitting diodes for example, to indicate the present state of charge.  
         [0014]     The charger  301  includes a microprocessor  311  and a voltage reference. The microprocessor  311  preferably includes on-board random-access memory, RAM, although peripheral memory would also suffice. The microprocessor  311  preferably includes communication ports  322  and analog-to-digital, A/D, converters  324 . One example of a microprocessor suited for this application is the uPD78F0034 series manufactured by NEC. This is an 8-bit microprocessor with 32 Kbytes of on-board flash memory and 1024 bytes of high-speed on-board RAM.  
         [0015]     The charger  301  includes several contacts for coupling to a battery. Typically, four contacts would be provided: a B+ contact  303  for supplying power to the battery, a B− contact  306  that serves as a return path, a Th contact  305  for sensing temperature, and a D contact  304  for identifying the battery. Temperature sensing may be done with a thermistor  310  disposed within the battery pack  302 . Identification may be done via either a coding resistor  308  or a memory device  309  with data stored therein. The charger  301  further includes a means of sensing current. One preferred means of sensing current is by way of a current sense resistor  325  coupled to an A/D converter  324 .  
         [0016]     The battery pack  302  contains the thermistor  310  for sensing the temperature of the cell(s)  307 , the optional code resistor  308 , which has an impedance that corresponds to a particular cell, and a memory device  309  that holds battery information, including serial number, type of cell, charging instructions, charge usage histogram, date of manufacture, first date of use, last time of charge, charge capacity, current charge level, and similar information. An example of such a memory device is the DS2400 and DS2500 series (e.g., the DS2433) manufactured by Dallas Semiconductor. Batteries of this construction are also taught in copending application Ser. No. 09/738,090, filed Dec. 15, 2000, entitled “Method and Mechanism to Prevent Corruption of Data”, which is incorporated herein by reference in its entirety for all purposes.  
         [0017]     Referring now to  FIG. 1 , illustrated therein is one preferred embodiment of method of determining the time until completion for a rechargeable battery in accordance with the invention. Data from the memory  309  disposed within the battery  302  is retrieved at step  101 . This data may include battery identification information, charging information, charging states, default times for completion of the charging states, and the like.  
         [0018]     The microprocessor  311  within the charger  301  then sets initial data values for the charging states at step  102 . In this exemplary embodiment, the primary states are rapid charge, wherein the battery is being charged at a high current, and trickle charge wherein the battery has reached near full capacity and the current has been reduced to a low level for top-off charging. The values for these states are initialized at step  102 .  
         [0019]     The charger  301  then determines the present state of charge at step  103 . The state of charge is a function of capacity, and may be read from the memory  309  in the battery  302 , read from a fuel gauging circuit or sensed by battery voltage, temperature or charging current. If the battery  302  is near full ccapacity, and the charging state is thus trickle charge, then the charger  301  will set the trickle charge in one of two ways: if the transition from rapid to trickle charging was captured by the charger  301 , then the charger  301  will set the trickle charge time variable equal to the default trickle charge time retrieved from the battery  302  less the time elapsed since the transition from rapid to trickle. If the transition from rapid to trickle was not captured, then the trickle time variable will be set to the default trickle charge time retrieved from the battery  302 , as it is in step  105 . If the present state is rapid charge (step  106 ), then the charger  301  may optionally compensate for self discharge loss at step  107 . This may be accomplished when the data stored within the battery  302  includes a time stamp, and when the battery includes a real time clock. The charger  301  reads the capacity, time stamp of last charge, default parasitic loss value(s), and current time from the battery  302 . The capacity, which represents the amount of energy stored within the battery, is then compensated by subtracting the product of elapsed time and default parasitic loss value(s) from the read capacity.  
         [0020]     The rapid charge time is then set at step  108 . This is done by first reading the tank size from the battery  301 . The tank size is the maximum energy capable of being stored within the battery  302 . The maximum energy capable of being stored may be based upon a factory calibration, as any one particular cell may be slightly different from another due to tolerances, storage conditions, time since manufacture, etc. The current charge level is then read from the battery. The charger  301  then subtracts the current charge level from the tank size. The result is then divided by the charging current. This yields a time to completion for the rapid charge state. The trickle charge time is then added to yield a total time to completion at step  109 . This value is forwarded to a display at step  10 .  
         [0021]     To summarize, a charger is provided. The charger is capable of coupling to a rechargeable battery. The charger includes a processor that is capable of identifying the battery. The charger then identifies the charging states for that particular battery. In the exemplary embodiment above, the charging states were rapid and trickle, although the invention is not so limited. Numerous other charging states, including an initiation charge for batteries that are below their recommended minimum threshold voltages, may be included.  
         [0022]     The charger then determines which state is being executed. The charger calculates a first time to completion for that particular state. The charger also calculates at least a second time to completion for another of the states. The first and second (as well as others if applicable) are summed to determine a total time of completion.  
         [0023]     Referring now to  FIG. 2 , illustrated therein is a second preferred embodiment of determining a time to completion in accordance with the invention. The method of  FIG. 2  is similar to that of  FIG. 1 , except a third charging state—discharging—is included. Steps  201 - 210  are analogous to steps  101 - 110  of  FIG. 1 .  
         [0024]     The difference occurs at step  206 . If the charging state is not rapid, the charger  301  optionally compensates for self-discharge loss at step  212 . The charger  301  then sets the rapid charging time to the tank size divided by the rapid charge current. This is done because the charger  301  knows that the battery  302  will be fully discharged at the completion of the discharge step.  
         [0025]     The charger  301  then verifies that the charging state is discharge at step  214 . If the charging state is not one of the allowable charging states, an error message is delivered at step  215 . If the charging state is discharge, the charger  301  calculates the discharge time by dividing the present battery charge level by the discharge current at step  216 .  
         [0026]     Revisiting step  206 , when the charging state is rapid, the charger  301  detects whether a transition from discharge to rapid charge was stored in memory at step  211 . If so, the charger  301  will skip the optional self discharge step  207 . The rapid charge time is calculated at step  208 . The total time to completion is computed at step  209  by adding the trickle charge time, the rapid charge time and the discharge time together.  
         [0027]     While the preferred embodiments of the invention have been illustrated and described, it is clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the following claims.