Abstract:
Apparatus and method for automatic recovery of sulfated lead acid batteries rely on monitoring battery voltage, current and internal resistance during battery charging. The lead acid battery is recovered for usage by measuring the internal resistance to see if it is so high such that the battery is unrecoverable, or so low such that the normal charging methods can be used. If the internal resistance is between the two limits, the battery receives a first constant charge current. As the lead acid battery is being charged slowly by a constant charge current, the battery voltage is measured. The decrease in the internal resistance (IR) of the battery causes the battery voltage to decrease during charging, while the charging causes the battery voltage to increase. According to the present invention, if it is detected that the battery voltage has reached the minimum voltage and begun to increase in a predetermined period of time, the charge current is substantially increased (e.g., doubled) because the capability of the lead acid battery to accept a higher charge current has increased. As the charge current is increased, the recovery and charging of the lead acid battery arc advantageously more expedient and efficient.

Description:
RELATED APPLICATIONS 
     The present application claims the priority of U.S. Provisional Application Ser. No. 60/128,891, entitled APPARATUS AND METHOD FOR AUTOMATIC RECOVERY OF SULFATED LEAD ACID BATTERIES, filed on Apr. 12, 1999, the entirety of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to lead acid batteries, and in particular, relates to an apparatus and method for automatic recovery of sulfated lead acid batteries. 
     BACKGROUND OF THE INVENTION 
     A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an oxidation-reduction electrochemical reaction. This type of reaction involves the transfer of electrons from one material to another. Batteries in the art commonly utilize electrochemical operations to store and release electrical energy. 
     FIG. 1 illustrates the electrochemical operation of a typical battery. Referring to FIG. 1, the negative electrode (anode  2 ) is the component capable of giving up electrons, being oxidized during the reaction. It is separated from the oxidizing material, which is the positive electrode (cathode  1 ), the component capable of accepting electrons. The transfer of electrons takes place in the external circuit  11  connecting the two materials and in the electrolyte  3 , which provides an ionic medium for the electron transfer in the battery  4 . 
     Certain types of batteries are rechargeable, such as lead acid batteries. A lead acid battery uses sponge lead for the negative electrode (anode  2 ), lead oxide for the positive electrode (cathode  1 ), and a sulfuric acid solution for the electrolyte  3 . The lead acid battery  4  is left in a charged condition when it is not being used. During discharge, the active material in the lead acid battery is converted into lead sulfate and the sulfuric acid solution is diluted, i.e., its specific gravity decreases. Lead sulfate is an insulator that inhibits the proper charging of the lead acid battery  4 . However, the lead acid battery  4  can be used after it is recharged. 
     To recover the lead acid battery, the lead sulfate is converted back to active material by charging the battery at a low current. If the lead acid battery is left in discharge for a long time, typically a few days, it becomes sulfated and difficult to recharge. The sulfated lead acid battery is discarded if it is not recoverable, which is wasteful and harmful to the environment. 
     Therefore, there is a general need in the art for an improved apparatus and method of recovering lead acid batteries. An efficient apparatus and method for recovering lead acid batteries, that avoids unnecessary waste, is needed. 
     SUMMARY OF THE INVENTION 
     The lead acid battery is stored by placing it in a charged condition when it is not in use. In storage, self-discharge occurs which causes the battery voltage to decrease. The internal resistance increases when the battery is left in storage for a long period of time due to the growth of lead sulfate crystals, especially if the battery is stored in a discharged condition. The lead acid battery is recovered for usage by charging the battery with a low constant current. As the lead acid battery is being charged slowly by a constant charge current, the battery voltage during charging approaches a minimum voltage in the battery recovery process. Then, the battery voltage gradually increases as the lead acid battery is being charged. As the recovery process is being implemented, the sulfate in the lead acid battery is converted to active material which also causes the battery voltage to decrease due to decreasing IR drop voltage. Due to the charging which causes the conversion of lead sulfate to the active material, the battery voltage increases. 
     According to the present invention, when it is detected that the battery voltage has reached the minimum voltage and begun to increase, the charge current is substantially increased (e.g., doubled) because the capability of the lead acid battery to accept a higher charge current has increased. As the charge current is increased, the recovery and charging of the lead acid battery are advantageously more expedient and efficient. 
     In an illustrative embodiment of the present invention, the internal resistance of the battery is measured. If it is above a recoverable limit, e.g., 5 ohms (Ω), it is discarded. If it is below a normal limit, e.g., 0.2 ohms (Ω), it is subjected to normal charging. If it is between these limits, the electrolyte level is checked and corrected if it is low. Then, a controlled charge of current, e.g., 0.5 amperes (A), is sent to charge the battery and the battery voltage is measured and compared to a minimum voltage. If the battery reaches the minimum within a preset time interval, e.g., one hour, the charge is increased, e.g., doubled. A test is then made to see if the charge current has exceeded a current limit. If it has not exceeded the current limit, the battery voltage is measured at the new level and, if it reaches another minimum, the charge is increased again. This is repeated until the battery has been charging for another time period, e.g., eight hours, or the current limit is reached, indicating that the battery recovery is completed and the battery is no longer sulfated. Then, normal charging is used to make the battery ready for use. 
     In another embodiment, if the battery voltage continues to increase after the predetermined period, the charging is stopped for a short period of time, e.g., five minutes, and then the process is repeated from the point of checking to see if the charge current has exceeded the limit. If the voltage is decreasing or remains the same, a check is made to see if the battery has reached the minimum and begun to increase. If it has, the charging is stopped for a second period of time, e.g., five minutes. Then, the process begins from the beginning, i.e., by measuring the internal resistance. 
     In an embodiment of the apparatus of the present invention, a computer or microprocessor is programmed to implement the process steps (as illustrated in the various embodiments herein) of the method of the present invention. The method steps can be advantageously reconfigured by reprogramming the computer or microprocessor, e.g., to implement a voltage control method as opposed to the embodiments in which the battery is charged by a controlled charge current. 
     In an embodiment of the voltage control method of the present invention, the lead acid battery is charged by a controlled charge voltage. The charge voltage is increased if the internal resistance of the battery is within a recoverable range. The charge voltage is increased until the battery current reaches a first current limit. Then, the battery is charged until the battery current reaches a second current limit, at which point the charge voltage is decreased. The charge voltage is also compared with a preset limit. The process steps of the voltage control method of the present invention are repeated until the charge voltage falls below the preset limit, at which point the battery is charged using normal charging. After the normal charging is complete, the battery is available for use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which like reference designations represent like features throughout the enumerated Figures. The drawings referred to herein will be understood as not being drawn to scale except if specifically noted, the emphasis instead being placed upon illustrating the principles according to the present invention. In the accompanying drawings: 
     FIG. 1 illustrates the conventional operation of a lead acid battery; 
     FIGS. 2 and 2A are a flow diagram illustrating an embodiment of the current control method of the present invention; 
     FIG. 2B is a graph illustrating the battery voltage response of a battery being recovered using the method of the present invention; 
     FIG. 3 is a flow diagram that illustrates another embodiment of the current control method of the present invention; 
     FIG. 4 is a diagram that generally illustrates an embodiment of the apparatus of the present invention; 
     FIG. 4A is a diagram that illustrates a further embodiment of the apparatus of the present invention; and 
     FIGS. 5 and 5A are flow diagram that illustrates an embodiment of the voltage control method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 is a flow diagram illustrating an embodiment of the current control method of the present invention. Referring to FIG. 2, the internal resistance (IR) of the lead acid battery is measured (step  201 ). The IR is checked against a recoverable limit in step  203 . If the IR of the battery is greater than the recoverable limit, e.g. 5 ohms (Ω), the battery is unrecoverable and a signal is sent to discard the battery or warn that the battery should be discarded (step  205 ). If the IR of the battery is not greater than the recoverable limit, the control flow is directed to step  207 . 
     The IR is checked against a normal limit in step  207 . If the IR is not greater than the normal limit, e.g., 0.2 ohms (Ω), the battery only requires normal charging to place it into condition for use, and the control flow is directed to step  223 . Normal charging of the battery is implemented in step  223 , in which various charging methods can be used, such as pulse current charging, constant current charging and constant voltage charging, which are known in the art. After the lead acid battery is charged, it is available for use. If the IR is greater than the normal limit, the control flow is directed to step  209 . 
     The electrolyte level of the battery is checked in step  209 . If the electrolyte level is low, i.e., the electrolyte level is below an acceptable level, a signal is sent in step  211  to correct the electrolyte level, e.g., by adding water or electrolyte into the battery. The control flow is then looped back to step  201  where the IR of the battery is measured again. 
     If the electrolyte level is not low, i.e., it is above an acceptable level, a controlled charge current, preferably 1 ampere (A) or less, is passed to charge the battery in step  213 . As the battery is being charged, the battery voltage is measured (step  215 ) for a preset period of time. The battery voltage is compared with a minimum voltage in step  217 . If the battery voltage has not reached a minimum voltage (after which it began to increase), the control flow is looped back to step  215  where the battery voltage is measured again. If the battery voltage has reached a minimum voltage, after which it has been increasing for a preset time interval, then the control flow is directed to step  219 , where the charge current is increased, e.g., by 50 or 100 percent. 
     Step  221  checks to see whether the charge current has exceeded a current limit. If the charge current (after the increase in step  219 ) does not exceed the current limit, then the control flow is looped back to step  213  where the controlled charge current continues to charge the battery and the process steps beginning at step  213  are repeated, i.e., the charge is increased and the voltage measured. If the charge current exceeds the current limit, then the recovery is complete and the battery is no longer sulfated. After normal charging (step  223 ), the battery is available for use. 
     FIG. 2A is a graph illustrating the battery voltage response of a battery charged using the method of the present invention. The graph, as shown in FIG. 2A, illustrates the relationship of the battery voltage and the charge current over a period of time. At time t 1 , the battery is charged with an initial current of 0.5 A. The battery voltage drops to a minimum and then slowly rises until t 2 . The charge current is increased to 1 A, according to the method of the present invention, in response to the behavior of the battery voltage before t 2 . Thereafter, the battery voltage drops due to the IR decrease during the conversion to the active material, and then stabilizes to a relatively constant voltage followed by a low rise in voltage until t 3 . Because of the increased charge current, the battery voltage is higher after t 2  than before t 2 . The sharp rise in voltage at t 2  is due to increased IR drop voltage caused by the current increase at t 2 . Similarly, at t 3 , t 4  and t 5 , the battery voltage drops to a minimum and then sharply rises, and the charged current is increased accordingly to 2 A, 4 A and 8 A, respectively. An advantage of the method of the present invention is that the battery can be quickly charged by substantially increasing the charge current once a specific behavior of the battery voltage is detected, as opposed to slowly charging the battery with a low, constant current. Furthermore, the method of the present invention is particularly advantageous because it can be entirely implemented in an automated fashion in programmable software in a computer that controls the recovery and charging of sulfated lead acid batteries. 
     FIG. 3 is a flow diagram that illustrates another embodiment of the current control method of the present invention. Referring to FIG. 3, the IR of the lead acid battery is measured (step  301 ). The IR is checked against a normal limit in step  303 . If IR is less than the normal limit, e.g., 0.2 ohms (Ω), the lead acid battery is not sulfated. The battery is recovered by normal charging using conventional charging methods as previously discussed (step  305 ). After the normal charging is complete, the battery is available for use. 
     If IR is not less than the normal limit, then the control flow is directed to step  307  where IR is tested against a recoverable limit. If IR is greater than the recoverable limit, e.g., 5 ohms (Ω), the battery is unrecoverable and a signal is sent to discard or warn that the battery should be discarded (step  309 ). If the IR of the battery is not greater than the recoverable limit, a controlled charge current is passed to charge the battery in step  311 . The charge current is tested against a charge current limit in step  313 . If the charge current is greater than or equal to the charge current limit, e.g., 8 amperes (A), the recovery is complete and the battery is charged in step  305  using normal charging methods (as discussed above). After normal charging is complete, the battery is available for use. 
     If the charge current is less than the charge current limit, then the charge current is increased, e.g., by 50 or 100 percent (step  315 ). As a result, the battery voltage gradually increases. The lead acid battery is monitored for a first time period (up to one hour in the present embodiment) in step  317 . If the battery voltage is still increasing after the first time period has expired, the charging is discontinued in step  321 . A second time period (five minutes in the present embodiment) is allowed to lapse (step  323 ) and the control flow is looped back to step  311 , where the process steps starting at step  311  are repeated. If the battery voltage is decreasing or remains the same, it is determined in step  325  whether the battery voltage of the lead acid battery has reached a minimum voltage and begun to increase for a time interval. If the battery voltage has reached a minimum voltage and begun to increase, the charging is discontinued in step  327 . The second time period is allowed to lapse (step  329 ) and the control flow is looped back to step  301 , where the IR of the battery is measured and the process steps starting at step  301  are repeated. 
     If the battery voltage has not reached a minimum voltage, it is determined in step  331  whether the lead acid battery has been charging for more than a third time period, e.g., eight hours in the present embodiment. If the charging has not lasted for more than 8 hours, the control flow is reverted back to step  325 . If the battery has been charging for more than 8 hours, the charging is discontinued in step  327 . The second time period (e.g., five minutes) is allowed to lapse (step  329 ) and the control flow is looped back to step  311  (via C), where the process steps starting at  311  are repeated. 
     FIG. 4 is a block diagram that generally illustrates an embodiment of the apparatus for carrying out the invention. Referring to FIG.  4 , programmed device  40  stores the process steps of the method of the present invention and computer or microprocessor  41  implements the process steps including those embodied in FIGS. 2,  3  and  5 . The method steps are programmed into programmed device  40 , which can be reconfigured by rewriting or reprogramming the software in programmed device  40 . Computer  41  is connected to data acquisition device  42 , which processes the data from battery  47  into a form useful for the computer  41  using methods such as analog-to-digital conversion, digital-to-analog conversion, amplification or noise reduction. Through data acquisition device  42 , computer  41  directs the charging of battery  47  by measuring the internal resistance (IR), voltage and current of battery  47 , as well as controlling the charge current and the charge voltage from a power supply  49 . The data acquisition device  42  collects IR, battery current or voltage data for computer  41  via analog-to-digital converter (ADC)  43 , which converts the data from analog to digital form, and processes the data from battery  47  into a form useful for computer  41 . Shunt  46 , which measures the charge current, forwards the charge current data to computer  41  via ADC  43  and data acquisition device  42 . Computer  41  can stop the charging of battery  47  for a period of time by discontinuing the transmission of the charge current from power supply  49 . Computer  41  can also direct the charging of battery  47  by controlling the charge current or charge voltage supplied by power supply  49 . Computer  41  can control power supply  49  by sending instructions via data acquisition device  42  and a digital-to-analog converter (DAC)  45  which converts digital signals from computer  41  into an analog form which can control power supply  49 . Control relay  48  can implement normal charging (as discussed above), such as current pulse charging, or place battery  47  in an open circuit by closing or opening in response to instructions by computer  41 . Computer  41  has control over control relay  48  by sending instructions thereto via relay module  44 . Control relay  48  acts like a switch by putting the battery in open circuit for a period of time (e.g., 5 minutes). 
     An embodiment of the operation of the apparatus of the present invention as shown in FIG. 4 is described herein in conjunction with FIG.  3 . In particular, battery  47  sends IR data to computer  41  via ADC  43 , which converts the IR data from analog to digital form, and data acquisition device  42 , which reduces the noise in the IR data and amplifies it for use by computer  41 . Computer  41  checks the IR of battery  47  against a normal limit. If IR is less than the normal limit, e.g., 0.2 ohms (Ω), battery  47  is not sulfated. Computer  41  then directs control relay  48  and power supply  49  to use normal charging to recover battery  47  using conventional charging methods as previously discussed (step  305 ). After the normal charging is complete, battery  47  is available for use. 
     Referring to step  307 , the IR of battery  47  is not less than the normal limit, then computer  41  checks the IR against a recoverable limit, e.g., 5 ohms (Ω), which is dependent on the output capacity of power supply  49 . If the IR is greater than the recoverable limit, battery  47  is unrecoverable and computer  41  sends a signal to discard or warn that the battery should be discarded (step  309 ). If the IR is not greater than the recoverable limit, computer  41  instructs power supply  49  to send a controlled charge current to charge battery  47  (step  311 ). Computer  41  checks the charge current against a charge current limit (step  313 ). If the charge current is greater than or equal to the charge current limit, e.g., 8 amperes (A), the recovery is complete and computer  41  instructs control relay  48  and power supply  49  to charge battery  47  (step  305 ) using normal charging methods (as discussed above). After normal charging is complete, battery  47  is available for use. 
     If the charge current is less than the charge current limit, then computer  41  instructs power supply  49  to increase the charge current, e.g., by 50 or 100 percent (step  315 ). As a result, the battery voltage gradually increases. computer  41  monitors battery  47  for a first time period, e.g., for one hour in the present embodiment (step  317 ). Battery  47  continues to send battery voltage data to computer  41  via ADC  43  and data acquisition device  42 . If the battery voltage is still increasing after the first time period has expired, computer  41  instructs power supply  49  to stop charging battery  47  (step  321 ). Computer  41  waits for a second time period, e.g., five minutes, to lapse (step  323 ), then repeats the process steps starting at step  311 . If the battery voltage of battery  47  is decreasing or remains the same, computer  41  checks to see whether the battery voltage of battery  47  has reached a minimum voltage and begun to increase for a time interval (step  325 ). If the battery voltage has reached a minimum voltage and begun to increase, computer  41  instructs power supply  49  to stop charging battery  47  (step  327 ). Computer  41  waits for the second time period (e.g., five minutes) to lapse (step  329 ). Computer  41  then repeats the process steps starting at step  301 . 
     If the battery voltage has not reached a minimum voltage, then computer  41  determines whether power supply  49  has been charging battery  47  for more than a third time period, e.g., eight hours (step  331 ). If the charging has not lasted for more than 8 hours, computer  41  repeats the process steps starting at step  325 . If the battery has been charging for more than 8 hours, computer  41  instructs power supply  49  to stop charging battery  47  (step  327 ). Computer  41  waits for the second time period, e.g., five minutes, to lapse (step  329 ), and then repeats the process steps starting at step  311 . 
     FIG. 4A is another embodiment of the apparatus of the present invention. The apparatus of the present invention as shown in FIG. 4A includes thermocouple module  42 A, thermocouple  47 A, electronic load  49 A, and diode  49 B, which are elements additional to the apparatus as shown in FIG.  4 . The apparatus of FIG. 4A essentially performs the same functions as the one shown in FIG. 4, except functions performed by thermocouple module  42 A, thermocouple  47 A, electronic load  49 A, and diode  49 B. Computer or microprocessor  41  can monitor the battery temperature of battery  47  using thermocouple  47 A (via thermocouple module  42 A). Computer  41  can stop charging battery  47  if the battery temperature measured by thermocouple  47 A is too hot, e.g., exceeds a tolerable limit. Moreover, electronic module  49 A can discharge battery  47 , and diode  49 B can protect power supply  49  by stopping the current into power supply  49  from battery  47  when the power supply voltage is low or when the electrical power to power supply  49  fails. 
     The present invention is particularly advantageous because its process steps can be implemented in computer or microprocessor  41  in an automated fashion, and can be reconfigured by reprogramming the programmed device  40 . Computer or microprocessor  41  can also be programmed (vis-a-vis the programmed device  40 ) to charge battery  47  with a controlled charge voltage, instead of the current control method in various embodiments as shown in FIGS. 2 and 3. 
     FIG. 5 is a flow diagram that illustrates another embodiment of the voltage control method of the present invention. Referring to FIG. 5, the internal resistance (IR) of the lead acid battery is measured (step  501 ). It is determined in step  503  if the IR is in a recoverable range, e.g., between 0.2 to 5 ohms (Ω). If the IR is not within the recoverable range, the battery is unrecoverable and a signal is sent to discard or warn that the battery should be discarded (step  504 ). If the IR of the battery is within the recoverable range, the charge voltage is increased (step  505 ). Step  507  checks the battery current against a first current limit. If the battery current has not reached the first current limit, then the control flow reverts back to step  505  where the charge voltage is further increased and the process steps starting at step  505  are repeated. If the battery current has reached the first current limit, the battery is charged with the increased voltage (step  509 ). 
     Step  511  checks the battery current against a second current limit. If the battery current has not reached the second current limit under a constant charge voltage, then the control flow reverts back to step  509  where the battery is charged with the charge voltage and the process steps starting at step  509  are repeated. If the battery current has reached the second current limit, the charge voltage is decreased in step  513 . 
     Step  515  checks the battery current against the second current limit. If the battery current has not reached the first current limit, then the control flow reverts back to step  513  where the charge voltage is decreased and the process steps starting at step  513  are repeated. If the battery current has reached the first current limit, the control flow is directed to step  517 . 
     Step  517  checks the charge voltage against a preset limit. If the charge voltage is greater than the preset limit, the control flow reverts back to step  509  where the battery is charged and the process steps beginning at step  509  are repeated. If the charge voltage is less than or equal to the preset limit, normal charging (as discussed above) is performed on the battery in step  519 . After the normal charging is complete, the battery is available for use. 
     The method and apparatus of the present invention can be used in any application that utilizes lead acid batteries, such as automotive starting, lighting, ignition, (SLI), lawnmowers, tractors, marine, float service. Other applications include motive power, stationary, or sealed battery uses, such as industrial trucks, materials handing, submarine power, emergency power, utilities, uninterruptible power supply (UPS), television, portable tools, lights, home appliances, radios, cassette and compact disc players, etc. 
     The foregoing embodiments demonstrate methods and devices implemented and contemplated by the inventors in making and carrying out the invention. While the invention has been particularly shown and described with reference to the preferred embodiments thereof, the embodiments are not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. Numerous equivalent methods, devices, and teclniques may be employed to achieve the same result. Similarly, any process steps described may be interchangeable with other steps in order to achieve the same result. It is intended that the scope of the invention is defined by the following claims and their equivalents.