Abstract:
A charge maintenance system for a lead-acid battery includes a charger, a voltage monitor, and a load/switch series combination, all connectable in parallel across the battery terminals, the switch and the charger being under control of a microprocessor. The battery is initially loaded for a predetermined time period, or until the battery voltage drops below an absolute minimum reference level during a loading cycle, and the system stores the lowest battery terminal voltage occurring during the loading cycle. After a predetermined delay following the loading cycle the charger is activated to charge the battery until it reaches a maximum charge level. Then, if the stored lowest battery voltage level is below a predetermined reference level, the loading/charging routine is repeated, otherwise it is not and the battery is considered good. If the stored lowest battery voltage level remains below the threshold for ten consecutive loading cycles, the system indicates that the battery failed the test but could be subject to retest. If the stored lowest battery voltage level is below an absolute minimum reference voltage level after three consecutive loading cycles, the system indicates that the battery is bad and should be discarded.

Description:
RELATED APPLICATION 
     This application claims the benefit of the filing date of copending U.S. Provisional Application No. 60/168,606, filed Dec. 2, 1999. 
    
    
     BACKGROUND 
     This application relates to battery charging systems and, in particular, to systems for charging, and maintaining the charge level of, lead-acid batteries, particularly thin-film lead acid batteries of the type manufactured by Johnson Controls, Inc., under the designation “Inspira,” or by Bolder Technologies, under the designation “Bolder 9/5 sub-C T.F.” (Thin Metal Film). 
     Certain kinds of lead-acid batteries, such as thin-film lead-acid batteries, must be carefully maintained in order to avoid degradation. Thus, fully-charged batteries of this type must have their charge maintained by a trickle charging system when the battery is not in use, otherwise the battery could become inoperable after about of month of non-use. Furthermore, after the battery has been discharged in use, it must be recharged promptly to avoid degradation. Waiting to recharge could result in serious deterioration and, if left too long, the damage could become irreversible. 
     Batteries which have been degraded through improper maintenance may be difficult to recharge after use. Thus, while they may reach a specified voltage during charge, they may be unable to maintain a suitable voltage under load. 
     SUMMARY 
     This application describes an improved battery charging system which avoids the disadvantages of prior systems, while affording additional structural and operating advantages. 
     An important aspect is the provision of a battery charging system which can improve the performance of lead-acid batteries which have become degraded through improper maintenance. 
     Another aspect is the provision of a charging system of the type set forth, which can maintain the condition of lead-acid batteries. 
     Another aspect is the provision of a battery charging system of the type set forth which is of relatively simple and economical construction. 
     Still another aspect is the provision of a battery charging system of the type set forth which is automatically controllable. 
     Certain ones of these and other aspects maybe attained by providing a charge maintenance system for a lead-acid battery comprising: a charger circuit adapted to be coupled to the battery for rapid charging thereof, a load and a switching device adapted to be connected in series across the battery, a voltage monitor circuit adapted to be coupled to the battery for monitoring the terminal voltage thereof, and a processor coupled to the charger circuit and to the switching device and to the monitor circuit and responsive to battery terminal voltage for controlling operation of the charger circuit and the switching device, the processor operating under stored program control for subjecting the battery to alternate loading and charging cycles until a predetermined battery voltage criterion is met. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. 
     FIG. 1 is a partially schematic and partially functional block diagrammatic view of a battery charging system; 
     FIG. 2 is a graph of battery voltage versus time illustrating the operation of the charging system of FIG. 1; and 
     FIG. 3 is a flow chart of the program routine for the microprocessor of the system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, there is illustrated a battery charging system, generally designated by the numeral  10 , for charging a battery  11 , which is preferably a thin-film, lead-acid battery. The charging system  10  includes a power supply  12  which is coupled by a plug  13  to a 120 V AC source. The power supply  12  provides appropriate supply voltages to a battery charger  14  and to a microprocessor  15 . The charger  14  may be of a known design, and is coupled across the terminals of the battery  11  for providing charging voltages and currents thereto. More specifically, the charger  14  is designed to provide fast charging of the battery  11 . 
     The system  10  also includes a voltage monitor  16  connected across the battery terminals for monitoring the battery voltage and providing an output signal indicative of that voltage to the microprocessor  15 . A load circuit  17  is connected across the battery terminals through a suitable switching circuit  18 , which operates under control of the microprocessor  15 . A display  19  is preferably also coupled to the microprocessor  19  for displaying suitable messages to the operator of the system. 
     An operating principle of the system  10  is that maximum battery performance of a lead-acid battery can be maintained, or such a battery which has been severely depleted or degraded can be rejuvenated, by subjecting the battery to one or more controlled discharge/charge cycles. While chargers using a single discharge/charge routine have heretofore been used in connection with nickel cadmium or nickel metal hydride batteries, it has not heretofore been recognized that such a routine can be of value in maintaining and/or rejuvenating lead-acid batteries, nor has repetition of such a routine been heretofore used. 
     Referring now also to FIG. 2, the details of the operation of the system  10  will be described. FIG. 2 illustrates a waveform  20  of the battery output voltage plotted against time during operation of the battery charging system  10 . First, the battery  11  is connected to the system  10  in the manner illustrated in FIG.  1  and the system  10  is plugged into the AC source and turned on. Initially, the charger  14  is controlled by the microprocessor  15  and is off. The microprocessor  15  first closes the switch  18  for connecting the load  17  across the battery  11  at “START.” The load  17  is selected to draw a heavy current from the battery  11 , such as from about 50 amps to about 200 amps, and during this loading the battery voltage drops rapidly, as at  21 . The load  17  is applied for a predetermined, relatively short time period t, which may, for example, be from about 10 seconds to about 40 seconds, depending upon the load current, and then the switch  18  is opened, disconnecting the load  17 . 
     The microprocessor  15  senses and stores in associated memory (not shown) the lowest battery voltage reached during loading, this valley being designated  22  in FIG.  2 . In the illustrated embodiment, the voltage dropped to 9.3 volts, but it will be appreciated that it could drop as low as a prescribed absolute minimum reference voltage level  23  (which might be from about 8.0 volts down to about 5.0 volts, depending on load chosen), depending upon the condition of the battery. If the voltage drops below the absolute minimum level  23 , loading is immediately terminated. Upon termination of loading, either at the end of the prescribed time period t, or by low voltage cut-off, the battery rests for a predetermined time, such as 30 seconds, while an indicator in the display  19 , such as an LED array  19   a , displays the load result (green means passing, yellow means failing voltage criteria, red means unable to maintain absolute minimum voltage). Following the 30-second rest, the microprocessor  15  directs the charger  14  to apply a fast-charging current to the battery  11 , as at  24 . Typically, the battery  11  will be charged beyond the nominal full-charge voltage level  25 , in this case indicated to be 13.0 volts, to a maximum voltage level at  26 , which could be as high as about 16.5 volts. It is characteristic of lead-acid batteries that, if charging continues beyond the maximum charge level  26 , the battery voltage will begin to drop. The charger  14  senses this drop in voltage at  27  by use of any of a number of techniques, such as detecting the transition of the waveform  20  from a positive slope to a negative slope. At that point, the charger  14  recognizes that the maximum voltage level has been achieved and thereupon terminates charging. 
     It is a significant aspect of the invention that the system stores a predetermined voltage threshold or reference level  28 , in this case 9.5 volts, and compares the minimum voltage level at  22  with the threshold, and the result of that comparison determines the remainder of the charging routine. Thus, if the minimum battery voltage during loading is at or above the threshold, then the system recognizes that no additional conditioning is necessary, whereas if the minimum voltage level during loading is below the threshold, further load/charge cycling is required. After each charging cycle, a determination is made of how to proceed. If the most recent load voltage of the battery did not fall below the threshold level  28 , the microprocessor ceases operation, except to display a “final disposition” indication, such as by an LED array  19   b , which is green to indicate a good battery. If the microprocessor has counted 10 load/charge cycles, in which the battery voltage fell below the threshold level  28 , the microprocessor ceases operation, except to display a “final disposition” indication by illuminating a yellow LED to indicate that the battery did not pass. The user can choose to start the program once again, or discard the battery as bad. If the microprocessor has counted at least three load/charge cycles, and in the current loading cycle the battery fell below the absolute minimum voltage level  23 , the microprocessor ceases operation, except to display a “final disposition” by illuminating a red LED to indicate that the battery should be discarded without further testing. If none of the three conditions, described above, occurs, then the microprocessor directs switch  18  to reconnect load  17 , thus beginning another load/charge cycle. 
     In the illustrated embodiment, the valley  22  is below the threshold  28 , so the system initiates another charge/discharge cycle. 
     More specifically, the microprocessor  15  reactivates the switch  18  to reconnect the load  17  for another loading cycle, followed by another charging cycle. In this case, the minimum voltage level  29  reached during loading is again below the threshold  28 , so a further load/charge cycle is initiated. After the next loading and charging cycle, the minimum voltage reached at  30  is now above the threshold  28 . Thus, the microprocessor  15  recognizes that no further conditioning is required. Accordingly, the microprocessor  15  ceases operation, except to display a “final disposition” indication by illuminating a green LED to indicate a good battery, and the battery voltage settles to the nominal full-charge level  25 . 
     It will be appreciated that the actual battery voltage levels being sensed by the voltage monitor  16 , as well as other data and messages indicating the general condition of the battery  11  and the current stage of the charging routine, can be displayed to a user on the display  19 . If desired, the display  19  may be of a type to also display the waveform  20 . 
     Referring to FIG. 3, there is illustrated a flow chart of the program routine executed by the microprocessor  15 , and generally designated by the numeral  40 . At the start, when the system is turned on, the routine first, at  41 , sets CYCLE equal to zero and then, at  42 , closes the load relay switch  18 , connecting the load  17  across the battery  11 , and then, at  43 , establishes DCOUNT equal to zero and resets LOW and VLOW flags. Then, at  44 , increments CYCLE by 1 and then, at  45 , turns on the load indicator, such as by illuminating a green LED in the array  19   a  signifying that the loading cycle is operating, and that the battery terminal voltage has not yet dropped below any reference levels. Then, at  46 , the routine delays one second and then, at 47 increments DCOUNT by one, DCOUNT representing the time in seconds that the load has been connected to the battery in the current loading cycle. 
     Next, at  48 , the routine checks to see if the battery terminal voltage has dropped below the predetermined reference voltage level  28 , i.e., 9.5 volts in the illustrated example. If it has, the load indicator is changed to yellow at  49  and then the LOW flag is set at  50 . Then, at  51 , the routine checks to see if the battery terminal voltage has dropped below the absolute minimum voltage level  23 , i.e., in the illustrated example 5.0 volts. The routine proceeds directly to  51  from  48  if, at  48 , the battery terminal voltage is not below the first reference level. If, at  51 , the battery terminal voltage is below the absolute minimum value the routine then sets the load indicator to red at  52 , and sets the VLOW flag at  53 . If, at  51 , the battery terminal voltage is not below 5.0 volts, the routine then checks at  55  to see of DCOUNT is greater than 9. If it is not, the routine returns to  45  to continue the loading cycle. If, at  54 , DCOUNT is greater than 9, this means that the loading cycle has lasted for the predetermined time period, in this case 10 seconds, so the routine then proceeds to  55  to open the load relay switch  18  and disconnect the load  17  from the battery. The routine goes directly to  55  from  53 . After the load is disconnected, the routine waits for a 30-second delay period at  56  and then turns off the load indicator at  57 . 
     The program then checks at  58  to see if the current loading cycle is at least the third such cycle. If so, the program then checks at  59  to see if the VLOW flag is set and, if it is, indicating that the battery terminal voltage is below the absolute minimum voltage level  23 , the program then moves to  60  to set the battery condition or final indicator to red, indicating that the battery should be discarded, whereupon the program is ended. 
     If, at  58 , the current loading cycle is less than a third or, at  59  the VLOW flag is not set, the program then proceeds to  61  to activate the battery charger  14  and then checks at  62  to see if the charging is complete, i.e., the charger is turned off, and continues checking for this condition. When the charging is complete, the routine checks at  63  to see if the LOW flag is set, indicating that during the preceding loading cycle the battery terminal voltage had dropped below the predetermined reference level  28 . If not, the battery condition indicator is set to green at  64  indicating that the battery is good, and the program is ended. If, at  63 , the LOW flag is set, the program checks at  65  to see if this is the tenth loading cycle. If not, it waits another 30-second delay period at  66 , and returns to  42  to start another loading cycle. If, at  65 , the current loading cycle is the tenth, the routine sets the battery condition indicator to yellow at  67 , indicating that the battery voltage has remained below the reference level  28  for 10 consecutive loading cycles, so that the battery has failed the test, but could be eligible for further testing. Then the program is ended. 
     While, in the illustrated embodiment, the nominal full-charge level  25 , the threshold level  28  and the absolute minimum level  23  are, respectively, designated as 13.0 volts, 9.5 volts and 5.0 volts, it will be appreciated that this is simply for purposes of illustration, and that different voltage levels could be used, depending upon the particular application. Similarly, the loading time t may be varied, as desired. While, in the illustrated embodiment, the load  17  is fixed, it will be appreciated that a variable load could be utilized, in which case the variation could be under the control of the microprocessor  15 , as indicated by the dotted line  35  in FIG.  1 . 
     From the foregoing, it can be seen that there has been provided an improved battery charging system which is capable of maintaining and rejuvenating lead-acid batteries. 
     The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While a particular embodiment has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants&#39; contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.