Abstract:
A cell balancing software program that executes on a computer system embedded inside a multi-cell battery and includes a means to control an external charging system. When a charge imbalance is detected between the cells, a cell balancing algorithm is selected from a plurality of cell-balancing algorithms and is executed. The executed algorithm causes a charge request, which specifies desired charging parameter(s), to be generated, and the charge request is transmitted to the external charging system. After the external charging system charges the battery according to the charge request, the effectiveness of the cell-balancing algorithm can be evaluated and stored in a history. The history can be used to select cell balancing algorithm(s) for future cell balancing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following applications that have all been filed by the present inventors. Ser. No. 12/321,310 filed on Jan. 15, 2009 and entitled “Embedded Monitoring System for Batteries”. Ser. No. 12/380,236 filed on Feb. 25, 2009 and entitled “Embedded Microprocessor System for Vehicular Batteries”. And Ser. No. 12/454,454 filed on May 18, 2009 and entitled “Embedded Algorithms for Vehicular Batteries”. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM LISTING ON CD 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to battery technology and the field of computers. In particular it relates to how a computer system embedded in a multi-cell battery can, in conjunction with an external intelligent charging system, perform cell balancing. 
     2. Prior Art 
     The typical automobile lead-acid starter battery consists of six electrochemical cells embedded in a polymer case. Because the cells are encased, cell voltage measurements cannot be taken, the temperature or pressure inside the battery is not known and for those batteries without filler caps the level of the electrolyte cannot be determined. 
     When the voltage of individual cells inside a lead-acid battery differ by as little as one one-hundredth of a volt, the health of the battery is in jeopardy. An imbalance causes weaker cells to become progressively undercharged and the stronger cells to suffer the consequences of being consistently overcharged. Unless this imbalance can be quickly ameliorated the battery will prematurely fail. 
     Cell balance is typically restored in lead-acid batteries by temporarily overcharging the battery at a voltage of 14.4 volts for 15 minutes in an attempt to bring weak cells into alignment. This approach is a risky proposition. The external charging system does not know the voltage of each individual cell so does not know if or when to apply a cell balancing routine nor will it know if the cell balancing attempt was successful. The external charging system also does not know the level of the electrolyte of each cell or the internal temperature and pressure of the battery. If the strong cells are excessively overcharged, their positive plates will disintegrate or buckle and the excessive temperature generated in the cell by overcharging will cause lose of electrolyte. On the other hand, if the weak cells are not sufficiently charged, the cell imbalance will remain and the battery will die prematurely. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention makes use of computer systems that are described by the present inventors in application Ser. No. 12/321,310 filed on Jan. 15, 2009 entitled “Embedded Monitoring System for Batteries”, application Ser. No. 12/380,236 filed on Feb. 25, 2009 entitled “Embedded Microprocessor System for Vehicular Batteries” and application Ser. No. 12/454,454 filed on May 18, 2009 entitled “Embedded Algorithms for Vehicular Batteries”. These computer systems are designed to reside inside the battery and include facilities for measuring the individual cell voltages, the electrolyte level of each cell and the internal temperature and pressure of the battery. These computer systems also have a means to store and execute battery management algorithms as well as exchange data and commands with external devices such as intelligent battery chargers and intelligent automobile alternator systems. 
     What is missing in the prior art is the ability to first detect a cell imbalance inside the lead-acid battery and then to carefully control the process by which the imbalance is ameliorated. The present invention makes use of a computer system that can detect such an imbalance. Once detected, a closed loop control path is established with an external intelligent charging system. Different charge requests are made of the intelligent charger. All the while the battery&#39;s internal state is carefully monitored to avoid permanent damage. 
     A series of charge requests followed by a proper assessment of the benefit of the charging procedure should be properly viewed as a cell-balancing algorithm. A cell balancing algorithm can be made to mimic the typical 14.4 volt flat charge rate of 15 minutes that is performed by many of today&#39;s battery chargers. A different cell balancing algorithm can be made to issue a much higher voltage request for a much shorter period of time. Still other algorithms can issue cyclic voltage requests that create pulse charging. At the termination of each algorithm a check is made to see if the cells have been brought back into balance. If not, a different algorithm is tried. 
     This invention can also be properly viewed as a research tool. There is a multitude of things that can cause a cell imbalance. Some examples are partial shorts between positive and negative plates, partial shorts between plates and straps, improper electrolytic levels, crystallized lead sulfate accumulations and incorrect specific gravity. This invention is heuristic in nature in that there is no established methodology that correlates or matches charging schemes to the underlying cause of a cell imbalance. A charging regime is tried by a cell balancing algorithm and its results are monitored. If the cell imbalance persists a different cell balancing algorithm is tried. This next charging regime may be similar to the previous attempt or may be radically different depending upon any detectable improvements. If no improvement occurred, the next charging regime will depart from the previous. The internal state of the battery continues to be monitored to insure no harm is being done. When a successful result is determined the successful technique is saved in a history file. This history is made readily available over the communication path normally established between battery and battery charging system. If the underlying cause of the imbalance is not apparent, such as plate sulfation, a post mortem can be performed on the battery in order to more properly correlate successful cell balancing techniques to the root cause of the imbalance. With this information battery manufacturers will have better insight into the failure mechanisms of their batteries while automobile and battery charger manufacturers will be able to build better charging systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a computer-based system shown embedded inside a flooded lead-acid battery that has six internal cells. This computer system includes a means for measuring cell voltages, cell electrolytic levels and battery temperature. The computer system includes a means to communicate with an external battery charging system. The computer system includes a means to execute algorithms that perform cell balancing by issuing charge request messages to an external charger. 
         FIG. 1A  is a flow chart illustrating the steps taken by one embodiment of the cell balancing computer program of this invention when it is executed by the computer system of  FIG. 1 . 
         FIG. 2  is a block diagram of a computer-based system shown embedded inside a sealed lead-acid battery that has six internal cells. This computer system includes a means for measuring cell voltages, pressure and battery temperature. The computer system includes a means to communicate with an external battery charging system. The computer system includes a means to execute algorithms that perform cell balancing by issuing charge request messages to an external charger. 
         FIG. 2A  is a flow chart illustrating the steps taken by another embodiment of the cell balancing computer program of this invention when it is executed by the computer system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following descriptions are provided to enable any person skilled in the art to make and use the invention and are provided in the context of two particular embodiments. Various modifications to these embodiments are possible and the generic principles defined herein may be applied to these and other embodiments without departing from the spirit and scope of the invention. Both embodiments described herein perform cell balancing by a computer system embedded inside a lead-acid battery. Special notification is made with regard to battery technology. The generic principles described herein apply to any battery type whose construction precludes the measurement of individual cell voltages. It is not necessarily limited to lead-acid batteries. Thus the invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles, features and teachings disclosed herein. 
     In accordance with one embodiment, the present invention makes use of a computer system that resides inside a flooded lead-acid battery. The computer system includes a means to measure individual cell voltages, the level of the electrolyte in each cell and the internal temperature of the battery. The computer system includes a means to communicate with an external battery charging system through the power cable attached to the battery. The computer system&#39;s central processing unit includes a means to measure time and includes facilities for storing data. The computer system&#39;s non-volatile memory includes algorithms that have a means to detect cell imbalances and to perform cell balancing by sending charge request messages to an external charging system. 
       FIG. 1  is a block diagram illustrating computer system  11  shown embedded inside flooded lead-acid battery  10 . Computer system  11  includes a data path to power connector  14  through transceiver  13 . Transceiver  13  is used to transfer information between central processor  12  and one or more external devices (not shown) attached conductively to power connector  14 . Sensors  30 - 35  measure individual cell voltages and pass this information to central processor  12 . Sensors  20 - 25  provide the level of the electrolyte in each of the battery&#39;s cells and pass this information to central processor  12 . Temperature sensor  15  measures the temperature inside the battery&#39;s case and passes this information to central processor  12 . 
       FIG. 1A  is a flowchart illustrating those steps taken by a cell balancing program when executed by central processor unit  12  of  FIG. 1  in order to detect and correct a cell voltage imbalance in battery  10  of  FIG. 1 . Execution of the cell-balancing program is initiated at step  40  of  FIG. 1A  by central processor  12  of  FIG. 1 . In step  41  of  FIG. 1A  the voltage of each cell is sampled by central processor unit  12  of  FIG. 1  using voltage sensors  30 - 35  of  FIG. 1 . At step  42  of  FIG. 1A  a comparison is made between individual cell voltages and program control transfers to either step  43  if an imbalance is detected or, if not, to step  52  where the cell balancing program is exited. At step  43  of  FIG. 1A  a cell balancing algorithm is selected from a number of possible algorithms. This selection is based on factors that include the extent of the imbalance, the age of the battery, the temperature of the battery and the level of the electrolytes. At step  44  of  FIG. 1A  the first step of the algorithm is executed. The first step causes central processor  12  of  FIG. 1  to send a charge request message to the external charging system attached to the power cable (not shown) through transceiver  13  and power connector  14  of  FIG. 1 . This, in turn, causes the voltage requested in the charge request message to be applied to battery  10  of  FIG. 1  by the external charging system (not shown). Program control then proceeds to step  45  of  FIG. 1A  where the level of the electrolyte of each individual cell is sampled by central processor  12  of  FIG. 1  using the electrolytic level sensors  20 - 25  of  FIG. 1 . At step  46  of  FIG. 1A  program control transfers to either step  48  of  FIG. 1A  if the electrolytic level of any cell is too low for the cell balancing algorithm to continue or to step  47  if the all the electrolytic levels are good. If program control transferred to step  48 , central processor  12  of  FIG. 1  will send an alarm message across the power cable (not shown) using transceiver  13  of  FIG. 1 . Program control then passes to step  52  where the cell balancing program is exited. If program control transferred to step  47  of  FIG. 1A  the temperature sensor  15  of  FIG. 1  is sampled and program control proceeds to step  49 . Step  49  causes program control to transfer to either step  51  of  FIG. 1A  if the battery&#39;s temperature is too high for the cell balancing algorithm to continue or, if not, to step  50 . At step  51  central processor  12  of  FIG. 1  sends a temperature alarm message across the power cable (not shown) attached to power connector  14  of  FIG. 1  and program control passes to step  52  where the cell balancing program is exited. If the temperature of the battery as read at step  47  of  FIG. 1A  is not excessive, step  49  of  FIG. 1A  causes program control to pass to step  50  of  FIG. 1A . At step  50  a check is made to see if the last step of the cell balancing algorithm has been executed. If the last step has not been executed, program control returns to step  44  where the next step of the cell balancing algorithm is executed and the balancing algorithm repeats. If the check at step  50  of  FIG. 1A  determines that the algorithm has finished, program control proceeds to step  41  of  FIG. 1A  and the cell balancing program repeats. 
     In accordance with another embodiment, the present invention makes use of a computer system that resides inside a sealed lead-acid battery. The computer system includes a means to measure individual cell voltages, the internal pressure of the battery and the internal temperature of the battery. The computer system includes a means to communicate with an external battery charging system through the power cable attached to the battery. The computer system&#39;s central processing unit includes a means to measure time and includes facilities for storing data. The computer system&#39;s non-volatile memory includes algorithms that have a means to detect cell imbalances and to perform cell balancing by sending charge request messages to an external charging system. 
       FIG. 2  is a block diagram illustrating computer system  61  shown embedded inside sealed lead-acid battery  60 . Computer system  61  includes a data path to power connector  14  through transceiver  13 . Transceiver  13  is used to transfer information between central processor  12  and one or more external devices (not shown) attached conductively to power connector  14 . Sensors  30 - 35  measure individual cell voltages and pass this information to central processor  12 . Pressure sensor  62  measures the pressure inside the sealed battery and passes this information to central processor  12 . Temperature sensor  15  measures the temperature inside the battery&#39;s case and passes this information to central processor  12 . 
       FIG. 2A  is a flowchart illustrating those steps taken by a cell balancing program when executed by central processor unit  12  of  FIG. 2  in order to detect and correct a cell voltage imbalance in battery  60  of  FIG. 2 . Execution of the cell-balancing program is initiated at step  70  of  FIG. 2A  by central processor  12  of  FIG. 2 . In step  71  of  FIG. 2A  the voltage of each cell is sampled by central processor unit  12  of  FIG. 2  using voltage sensors  30 - 35  of  FIG. 2 . At step  72  of  FIG. 2A  a comparison is made between individual cell voltages and program control transfers to either step  73  if an imbalance is detected or, if not, to step  2  where the cell balancing program is exited. At step  73  of  FIG. 2A  a cell balancing algorithm is selected from a number of possible algorithms. This selection is based on factors that include the extent of the imbalance, the age of the battery, the temperature of the battery and the level of the electrolytes. At step  74  of  FIG. 2A  the first step of the algorithm is executed. The first step causes central processor  12  of  FIG. 2  to send a charge request message to the external charging system attached to the power cable (not shown) through transceiver  13  and power connector  14  of  FIG. 2 . This, in turn, causes the voltage requested in the charge request message to be applied to battery  60  of  FIG. 2  by the external charging system (not shown). Program control then proceeds to step  75  of  FIG. 2A  where the internal pressure of the battery is sampled by central processor  12  of  FIG. 2  using the pressure sensor  62  of  FIG. 2 . At step  76  of  FIG. 2A  program control transfers to either step  78  of  FIG. 2A  if the battery&#39;s pressure is too high for the cell balancing algorithm to continue or to step  77  if the pressure is not excessive. If program control transferred to step  78 , central processor  12  of  FIG. 2  will send a pressure alarm message across the power cable (not shown) using transceiver  13  of  FIG. 2 . Program control then passes to step  82  where the cell balancing program is exited. If program control transferred to step  77  of  FIG. 2A  the temperature sensor  15  of  FIG. 2  is sampled and program control proceeds to step  79 . Step  79  causes program control to transfer to either step  81  of  FIG. 2A  if the battery&#39;s temperature is too high for the cell balancing algorithm to continue or, if not, to step  80 . At step  81  central processor  12  of  FIG. 2  sends a temperature alarm message across the power cable (not shown) attached to power connector  14  of  FIG. 2  and program control then passes to step  82  where the cell balancing program is exited. If the temperature of the battery as read at step  77  of  FIG. 2A  is not excessive, step  79  of  FIG. 2A  causes program control to pass to step  80  of  FIG. 2A . At step  80  a check is made to see if the last step of the cell balancing algorithm has been executed. If the last step has not been executed, program control returns to step  74  where the next step of the cell balancing algorithm is executed and the balancing algorithm repeats. If the check at step  80  of  FIG. 2A  determines that the algorithm has finished, program control proceeds to step  71  of  FIG. 2A  and the cell balancing program repeats. 
     Advantage 
     This invention changes the age old paradigm whereby the battery charging system blindly controls the procedure by which the cells in a multi-cell battery, such as the ubiquitous twelve volt lead-acid battery, can be kept in balance. With this invention the battery is now in control. A closed loop system is established with the charging device. The battery knows when a cell is out of balance. The battery possesses the means to learn from trial and error which charge strategy works best to reduce or remove cell imbalances. The battery monitors its internal state to insure that no harm is done. 
     Because this invention is a computer program that executes on a computer system embedded inside a multi-cell battery it has access to the voltage of each individual cell and therefore can detect a cell imbalance. 
     Because this invention is a computer program that executes on a computer system embedded inside a multi-cell battery that includes a means to communicate to external charging systems, this invention has a means to control the amount and duration of charge applied to the battery when a cell balancing operation is in progress. 
     Because this invention is a computer program that executes on a computer system embedded inside a multi-cell battery it has access to the internal temperature of the battery, access to the internal pressure of the battery if the battery is a sealed unit and access to electrolytic levels if the battery contains liquid electrolyte. With this information this invention can insure that the battery is not damaged by the aggressive charging schemes used by cell balancing procedures.