NZ312602A - Control and termination of a battery charging process - Google Patents

Abstract

A method and an apparatus for adjusting the process of charging a battery so as to charge the battery as rapidly as possible while avoiding overheating of or damage to the battery. The method provides for applying a charging pulse (C1) which provides an average charging current, applying a first depolarizing pulse (D1), waiting for a first rest period (DW1), measuring the voltage (V1) at a predetermined point within the first rest period, applying a second depolarizing pulse (D2), waiting for a second rest period (DW2), measuring the voltage (V2) at the predetermined point within the second rest period, determining a difference between the voltage (V1) and the voltage (V2), and taking corrective action, typically decreasing the average charging current if the difference is greater than a predetermined amount. The present invention also provides for determining whether the battery is low on water.

Description

5Bk 1 ' CONTROL AND TERMINATION OF A BATTERY CHARGING PROCESS" Technical Field This invention relates to battely chargers and, more particularly, to a method and an apparatus for controlling the charging process for a battery and for terminating the charging process Background of the Invention There are several methods of chargmg a battery and several methods of determining when to terminate the charging process for a battery These methods all suffer from the same problem they will overcharge a battery If a battery is overcharged it will produce oxygen 20 on the positive electrode This oxygen is then consumed by the negative electrode and the battery will heat up The risk of some damage to batteries due to overcharging is normal procedure for most charging techniques Battery manufacturers, to somewhat account for this, design battenes with extra negative electrode material However, overcharging 25 irreversibly consumes the negative electrode and, once the extra material is consumed, then future overcharging will reduce the amount of negative electrode available for the charge storage so the capacity of the battery will decline A well-documented effect of overcharging, particularly 30 using direct current charging, is that the battery voltage will decrease This decrease in the battery voltage is frequently referred to as minus delta V or negative delta V One method of determining the state of charge is to detect the occurrence of minus delta V and to termuiate the chargmg process on such occurrence However, this method will reduce 35 the battery life because the minus delta V occurs when an excess of oxygen is produced by the positive electrode and consumed by the negative electrode As a consequence, this method allows the battery WO 97/03489 PCT/US96/11466 temperature to nse and also allows pressure to build up inside the battery Another method of determininc when to terminate the charging process has been used when the battery is charged by forcing 5 pulses of current though the battery and applying a discharge pulse after each charging pulse In this method the charging process is terminated either in response to the average discharge current during the discharge pulse 01 in response to the ratio of energy removed by the discharge pulse compared to the energy provided to the battery duiing preceding 10 charging pulse However there is not a strong relationship between discharge voltage value and the state of charge of the battery Another method of terminating the charging process provides for sampling the terminal voltage of the battery between charging pulses a predetermined time after the beginning of the charge 15 Another method provides for measuring the battery voltage when a charging current is being applied and measuring the battery voltage during a discharging current The two voltage measurements are compared and the charging process is terminated when there is a predetermined difference between these voltages However, the 20 predetermined difference must be selected depending upon the type of battery being charged and the capacity of the battery being charged Furthermore, this method does not prevent the oxygen generating coincident with overcharging because it does not accurately determine the state of charge of the battery The reason is that, if the battery is 25 being charged at a fast rate of charge then, if there is a long discharge pulse, a mckel-cadmium (NiCd) or a mckel-metal-hydnde (NiMH) battery will heat up and the amplitude of charging voltage will change because of the change in battery temperature Thus, this method is not accurate for charging large batteries with a high speed of charge, 30 because a minor error in determining the battery status can result in damage to the battery To further complicate matters, the battery characteristics change during the charging cycle and vary from battery to battery Another method of controlling the charging cycle uses a 35 "resistance free voltage" reading The no-load ("resistance free") terminal voltage of the battery is measured after the end of a charging pulse This voltage is compared with a reference voltage to determine WO 97/03489 PCT/US96/11466 3 the charging current The reference voltage may be dependent upon, for example the ambient temperature the internal temperature, the internal pressure, the charging current, or a change in value in the charging current However, the measurement of the resistance free voltage must 5 occur when all the cells in the battery are in an equilibrium mode If an equilibrium condition has not been obtained then the voltage measurement of open circuit voltage can be different depending upon the time from the end of the previous charging pulse The equilibrium time depends on the charging current and the mass transfer capability of the 10 battery Also, the accuracy of the measurement of the resistance free voltage will depend upon the concentration of the electrolyte in the battery and the age of the battery The concentration of electrolyte will change, due to the porous structure of the plates surface, so measurement of the open circuit voltage milliseconds after the end of a chaigmg pulse 15 will not produce accurate results Thus, the battery can be overheated or destroyed Further, there are differences between batteries, differences between types of batteries, and differences in a single battery which occur dunng the charge cycle Thus, selection of the proper reference voltage may be difficult or very time-consummg 20 Any method which rapidly charges a battery must account for the constantly changing parameters of the battery, such as internal resistance, polarization resistance, mass transfer condition and temperature A rapid charging system typically uses a tapering current to avoid an overcharge condition and avoid gas production U S Patent 25 No 5,307,000 discloses using multiple discharge pulses between each charging pulse and provides for rapidly charging a battery with high charging pulse currents for a longer period of time, without marginal voltages per cell and heat production Without a plurality of depolarization pulses the voltage on the battery will nse very fast, due to 30 a rapidly increasing concentration of electrolyte around the electrodes, particularly at the end of a charging pulse A rapid charging process must be based on a reliable and precise method of charging control and charge termination Some previous charging methods have relied upon temperature cutoff, or 35 other methods that are not appropriate and/or uniform for all types of batteries, and methods that even required selection of the battery capacity even when used for charging ihe same battery type (lead-acid, WO 97/03489 PCT/US96/11466 4 NiCd, NiMH) Other previous charging methods have relied upon voltage cutoff However, a fixed voltage threshold is not reliable because the proper voltage threshold vanes, depending upon the condition of the battery, the temperature, and the battery's previous use and charge 5 history As is known in the prior art, the preferred technique for rapidly charging a battery involves forcing a high charging current into the battery, preferably by applying a senes of charging and depolanzmg pulses to the battery As the charging process becomes faster and the 10 instantaneous charging currents become higher, it is much more difficult to determine when the battery is fully charged and when the optimum time to terminate or modify the charging process occurs Without precisely knowing when the battery is fully charged, both charging time and energy are wasted due to overcharging of the battery 15 However, as stated above, overcharging causes gassing, generates heat, and increases pressure within the battery, thereby causing damage to the battsry or potentially initiating a catastrophic thermal runaway condition in the battery It is known that the battery is charged when the charging current has stabilized or has begun to increase after a 20 gradual decrease dunng a constant voltage charging mode. However, this method relies upon a change in the terminal charactenstics of the battery which occur when the battery is m close proximity to a thermal runaway condition Thus, it is desirable to determine if the battery is charged without the battery being close to entenng a thermal runaway 25 condition It is possible to avoid the problems of gassing, heating, thermal runaway, and other damage to the battery by reducing the chargmg currents, extending the charging time, or terminating the rapid charging process at an early point based upon some selected critena, for 30 example, the amount of time that the charging process has been applied, the ampere-hours of charge forced into the battery, or the battery temperature However, these methods may prematurely terminate the charging process, thereby leaving the battery in an undercharged condition, or substantially extend the time that is required for a 35 subsequent method, such as a tnckle charge, to bnng the battery to a full charge Also, using time or ampere-hours of charge as the determining cntena will cause catastrophic failure for a fully charged or nearly fully % WO 97/03489 PCT/US96/11466 charged battery if a rapid charging process is applied to the battery because the battery will not be able to accept the high charging pulse currents Ln this case, gassing and excessive heating of the battery will begin to occur almost immediately 5 Therefore, there is a need for a method of accurately determining the state of charge of a battery, especially during a rapid charging process, so that the rapid charging process can be used as long as possible, thereby bringing the battery to or very near a fully charged condition, but the rapid charging process will be terminated at a point 10 before damage occurs to the battery Further, dunng rapid charging process, at some point as the battery is becoming substantially charged, the battery may not be able to accept the full current from a charging pulse Thus, some of the charge current delivered during the charging pulse causes gassing and heating 15 However, terminating the rapid charging process at this time would be premature because the battery is not fully charged and is still amenable to a rapid charging process, but at a lower charging current Therefore, there is a need for a method of modifying a rapid charging process, as the battery is becoming charged, so as to continue rapidly charging the 20 battery m an efficient manner.

Therefore, there is a need for a method of modifying a rapid charging process, as the battery is becoming charged, so as to continue rapidly charging the battery in an efficient manner Summary of the Invention The present invention is directed to accurately determining when a battery is charged This allows a rapid charging piocess to be used as long as possible, thereby substantially chargmg the battery, but terminates the rapid charging process at a point which avoids 30 overcharging the battery and thus avoids wasted charging time and energy and damage to the battery In the present invention, to determine when a battery is charged, a charging pulse is applied to the battery and then at least two discharging (depolarization) pulses are applied to the battery The 35 battery voltage is measured at a predetermined point in a rest (wait) period after a first depolarizing pulse and at the same relative point in a rest period after a second depolarizing pulse The depolarizing pulse is % WO 97/03489 PCTAJS96/11466 created by applying a load across the terminals of the battery and is typically of a significantly shorter duration than the charging pulse When a charging pulse is applied to a lead-acid battery, the lead sulfate in the battery solution is converted into lead, lead oxide, and 5 electrolyte ions The lead and lead oxide are deposited on the respective electrodes The electrolyte ions are formed at the electrodes and surround the electrodes These electrolyte ions are dispersed by a transport phenomena due to the difference in the concentrations of the ions around the electrodes and the concentrations of the ions m the 10 solution When a battery is mostly uncharged, the concentration of the electrolyte is small Thus, the electrolyte ions formed around the electrodes are rapidly dispersed into the solution However, when the battery becomes mostly charged, the difference in the concentrations is 15 small and thus the ions disperse more slowly Until the ions disperse, the lead sulfate cannot move to the vicinity of the electrodes Thus, the ions form a barrier around the electrodes and prevent the electrodes from efficiently accepting another chargmg pulse Further, there is less of the solution which can be converted by the charging process Once this 20 occurs, the charging voltage must be increased in order to force the battery to accept the same amount of charging current However, increasing the charging voltage causes the water in the battery to disassociate into hydrogen gas and oxygen gas The oxygen gas is rapidly reabsorbed into the solution However, the hydrogen gas is 25 absorbed very slowly and so the battery internal pressure builds up If venting occurs the hydrogen gas is lost and so the battery has lost water The battery will fail if this occurs too many times Further, the higher voltage needed to charge the battery causes undesired heating of the battery and excessive heating may cause battery failure 30 The present invention discloses that the state of charge of the battery, that is, the concentration of the electrolyte m the solution, can be determined by measuring the open circuit voltage of the battery during rest periods following discharge pulses If the open circuit voltage is approximately the same from one rest period to a subsequent 35 rest period, then the battery is not being overcharged so the charging current need not be changed If the open circuit voltage decreases from one rest period to a subsequent rest period, then the battery is being WO 97/03489 PCT/US96/11466 * %rP ' overcharged or is being charged at a rate higher than the battery can accept so the charging current should be decreased or the charging process terminated Thus, when the battery becomes charged, the charging 5 current should be reduced to the level that the battery will efficiently accept Ln the present invention, the battery is determined to be efficiently accepting a charge and the charging current need not be changed as long as the second voltage measurement is approximately the 10 same as the first voltage measurement Also, in the present invention, the battery is determined to be mostly charged and the charging current should be reduced when the second voltage measurement is less than the first voltage measurement by some predetermined voltage difference (AVj 15 Thus, the present invention provides for accurately determining the state of charge of the battery in a rapid charging process and controlling or terminating the charging process to avoid damage to the battery Therefore, it is an object of the present invention to provide 20 a method of more precisely determining the state of charge of a battery by comparing the battery voltage between different rest periods or to at least provide the public with a useful choice The present invention provides a method for charging a 25 battery The method includes the steps of applying a charging pulse which provides an average charging current, applying a first depolarizing pulse, waiting for a firsi rest period, measuring the voltage of the battery at a predetermined Domt within the first rest period applying a second depolarizing pulse, waiting for a second rest period, 30 measuring the voltage of the battery at the predetermined point within the second rest period, determining a difference between the voltage at the predetermined point within the first rest penod and the voltage at the predetermined point within the second rest penod, and changing the average charging current depending upon the amount and polanty of this 35 difference In one aspect of the present invention the steps of applying the charging pulse, applying the first and second depolanzmg pulses, waiting for the first and second rest periods, and measuring the voltages 11 A^R 1BC9 iU C l IV LP 8 within the first and second rest periods are repeated if the difference is within specified limits In another aspect of the present invention the charging pulse has a charging pulse duration and the step of changing the average cnargmg current comprises changing the charging pulse duration In another aspect of the present invention the charging pulse has a charging pulse current amplitude and the step of changing the average charging current comprises changing the charging pulse current amplitude Ln another aspect of the present invention the charging pulse has a charging pulse repetition rate and the step of changing fhe average charging current comprises changing the charging pulse repetition rate In another aspect of the present invention each depolanzing pulse has a depolanzing pulse current amplitude and the method further includes changing the depolanzing pulse current amplitude when the average charging current is changed In another aspect of the present invention each depolanzing pulse has a depolanzing pulse duration and the method further includes changing the depolanzing pulse duration when the average charging current is changed In another aspect of the present invention a number of the depolanzing pulses follows each the charging pulse and the method furthei includes changing the number of the depolarizing pulses when the average charging current is changed The present invention also provides a method for charging a battery by a pulse charging process The method includes applying a charging pulse, applying a first depolanzing pulse, waiting for a first rest penod, measunng the voltage of the battery at a predetermined point within the first rest penod, applying a second depolanzing pulse, waiting for a second rest penod, measunng the voltage of the battery at the predetermined point within the second rest period, determining a difference between the voltage at the predetermined point within the first rest penod and the voltage at the predetermined point within the second rest penod, and terminating the pulse charging process if the difference is greater than a predetermined threshold The present invention also provides a method for determining the condition of a battery The method includes applying a % WO 97/03489 PCT/US96/11466 charging pulse to the battery, applying a first depolarizing pulse to the battery, waiting for a first rest penod, measuring the voltage of the battery at a first predetermined point within the first rest period, measuring the voltage of the battery at a second predetermined point 5 within the first rest penod, applying a second depolanzing pulse to the battery, waiting for a second rest penod, determining a difference between the voltage at the first predetermined point and the voltage at the second predetermined point, and indicating that water should be added to the battery if the difference is greater than a predetermined 10 threshold then The present invention also provides a method for terminating the charging process for a battery The method includes applying a charging pulse to the battery, applying a first depolarizing pulse to the battery, waiting for a first rest penod, measunng the voltage 15 of the battery at a first predetermined point within the first rest penod, measunng the voltage of the battery at a second predetermined point within the first rest penod, applying a second depolanzing pulse to the battery, waiting for a second rest penod, measuring the voltage of the baftery at a first predetermined point within the second rest penod, 20 measuring the voltage of the battery at a second predetermined point within the second rest penod, determining a first difference between the voltage at the first predetermined point within the first rest penod and the voltage at the second predetermined point withm the first rest penod, determining a second difference between the voltage at the first 25 predetermined pomt within the second rest penod and the voltage at the second predetermined point within the second rest period, and terminating the charging process if both the first difference is greater than a predetermined threshold and the second difference is greater than the predetermined threshold 30 Other objects, features, and advantages of the present invention will become apparent upon reading the following descnption of the prefened embodiment, when taken in conjunction with the drawings and the claims WO 97/03489 PCT/US96/11466 Brief Description of the Drawings Figure 1 is a block diagram of a battery charging circuit used in the present invention Figures 2A-2B show waveforms which illustrate a battery 5 charging process and how the state of charge of the battery is determined by comparing voltage measurements taken in different rest periods Figure 3 is a flow chart illustrating the process of determining the state of charge of the battery Figure 4 shows waveforms which illustrate a battery 10 charging process and how the condition of the battery is determined Figure 5 is a modification of the flow chart of Figure 3 which illustrates the process of determining the condition of the battery Detailed Description of the Invention Turning now to the drawing, Figure 1 is a block diagram of a battery charging circuit used in the present invention The battery charging and discharging circuit 10 comprises a keypad 12, a controller 13, a display 14, a charging circuit 15, a discharging (depolarization) circuit 16, and a current monitoring circuit 20 The keypad 12 is 20 connected to the "K" input of the controller 13 and allows the user to input specified parameters such as the battery type (lead a^.d, NiCd, NiMH, etc ) and other relevant information, such as nominal battery voltage or number of cells in series The keypad 12 may be a keyboard, dial pad, array of switches, or other device for entering information 25 To simplify operations by the user, the controller 13 may be preprogrammed with the parameters for a plurality of battery types In this case, the user would simply enter a battery type, such as a model number, and the controller 13 would automatically use the parameters appropriate for that battery type The display 14 is connected to the "S" 30 output of the controller 13 and displays the information, choices, parameters, etc , for the operator, and provides for audible and visible alarms or alerts for the operator The "C" output of the controller 13 is connected to the charging circuit 15 The charging circuit 15 provides a charging 35 current to the battery 11 Depending upon the application, the chargmg circuit 15 may be configured by the controller 13 to perform as a constant voltage source or as a constant current source The "D" output WO 97/03489 PCT/US96/11466 li of the controller 13 is connected to the discharging (depolarization) circuit 16, which may be configured by the controller 13 to provide a constant depolarization current to the battery 11, apply a selected load to the battery 11, or apply a lower voltage or a reverse voltage to the 5 battery 11 The pulse width of the pulses provided by circuits 15 and 16 are controlled by the controller 13 The output of the charging circuit 15 and the discharging circuit 16 are connected to the positive terminal of the batter)^ 11 via conductor 21 The negative terminal of the battery 11 is connected to circuit ground through a current monitoring resistor 10 20 Current flowing into or out of the battery 11 may therefore be determined by measunng the voltage across the current monitoring resistor 20 on conductoi 22 The current monitoring resistor 20 therefore functions as a current monitor and current hmiter Of course, other devices may be used to determine battery current 15 Battery voltage is monitored by measuring the voltage between conductor 21 and circuit ground The effects of the current monitoring resistor may be eliminated by measunng the voltage between conductors 21 and 22, or by subtracting the voltage on conductor 22 from the voltage on conductor 21 Conductors 21 and 22 are connected 20 to the "V" and "I" input, respectively, of the controller 13 Battery piesence may be determined by activating the chargmg circuit 15 and monitoring the output of the current monitoring resistor 20 to determine if charge current is flowing, by activating the discharging circuit 16 and monitoring the output of the current 25 monitonng resistor 20 to determine if charge current is flowing, by monitonng the voltage with both circuits 15 and 16 deactivated to determine if a battery is present, etc Temperature sensor 23 monitors the temperature of the battery 11 so that the controller 13 can adjust the magnitude, number, 30 and duration of the charging pulses and the depolarizing pulses and the duration of the rest penods in order to maintain the desired battery temperature Temperature sensor 23 preferably is immersed in the electrolyte solution of each battery cell to accurately report the internal battery temperature, even though only one is shown m the drawing 35 Temperature sensor 23 can be a thermostat, thermistor, thermocouple, or the like and is connected to the "T" input of the controller 13 % WO 97/03489 PCT/US96/11466 12 The controller 13 comprises a microprocessor, a memory, at least part of which contains operating instructions for the controller 13, timers, and an analog-to-digital converter Using a microprocessor-based controller is advantageous because a microprocessor can make 5 very rapid decisions, store voltage and current measurement data and perform calculations on data, such as averaging, comparing, and detecting peaks The timers, which can be discrete or implemented by the microprocessor, may be used for controlling the duration of any charging pulses, depolanzing pulses, or rest periods as well as providing 10 time references between consecutive depolanzing pulses or rest periods The analog-to-digital converter, which can be discrete or implemented by the microprocessor, may be used to convert the voltage or current signals into a form usable by the digital microprocessor A digital controller is discussed because it is the preferred embodiment, but an 15 analog controller may also be used to implement the present invention Figures 2A-2B show waveforms which illustrate a battery charging process and how the state of charge of the battery is determined The state of charge is determined by comparing voltage measurements taken in different rest periods The voltage and current 20 waveforms generally illustrate the charging process which applies one or more charging pulses CI, preferably followed by a rest penod CW1, and a plurality of depolanzing pulses D1 - D3, each depolarizing pulse D1 - D3, preferably followed by a rest period DW1 - DW3, respectively For convenience of illustration, the charging pulses and depolanzing pulses are illustrated as rectangular pulses but it should be appreciated that this is often not the case in actual practice and thus the present invention should be understood to include, but not be limited to, rectangular waveforms Also, for convenience only and not by way of 30 limitation, the charging pulses CI, CI' are shown to have the same pulse width and the same charge current amplitude IA, and the depolanzing pulses D1 - D3 are shown to have the same pulse width and the same discharge current amplitude IB Additionally, the number of depolanzing pulses shown is purely for convenience and not by way of 35 limitation The rest penods CW1 and DW1 - DW3 are shown to be of the same duration only for convenience and not by way of limitation 13 The controller 13 may alter the duration of such rest periods based on monitored changes in the state of charge of the battery First, with respect to comparing voltage measurements taken in different rest periods, specific voltage measurements VI and V2 5 are shown on the voltage waveform in Figures 2A - 2B VI and V2 are output voltage measurements of the battery taken when the battery is m an open circuit configuration during rest periods DW1 and DW2, respectively It should be understood that the first output voltage measurement VI can be made in the beginning, middle, or end of the 10 rest penod DW1, so long as the subsequent output voltage measurement V2 is taken at the same relative point in the next rest period DW2 The voltage levels dunng rest periods DW1 - DW3 are measured and evaluated by the present invention In Figure 2A it is seen that the voltage VI is approximately 15 equal to the voltage V2 This approximate equality in voltage indicates that this battery is being not being overcharged Therefore, the charging current IA need not be adjusted In Figure 2B it is seen that the voltage VI is greater than the voltage V2 If the difference between VI and V2 in Figure 2B is less 20 than 10 millivolts per cell then the charging current IA need not be adjusted However, if the difference between VI and V2 m Figure 2B is greater than 10 millivolts per cell then this decrease in voltage from VI to V2 indicates that this battery is being overcharged This may be ^je to the battery reaching a full charge or may be due to the battery being 25 unable to accept the full charging current IA for the duration of CI for whatever reason Therefore, the charging current IA should be decreased until the difference is less than 10 millivolts per cell FIG 3 is a flowchart for detenmning if a battery is charged by comparing voltage measurements taken dunng one or more rest 30 penods In step 301, the initial charging parameters are set by the user, such as the battery voltage or number of cells in the battery and the discharge rating (C) for the battery The controller 13 then determines the charging current IA and the depolanzing current IB for the battery This may be based upon a look-up table or an equation, as preferred 35 In step 303 the controller 13 applies a charging pulse CI of current amplitude IA to the battery, preferably but not necessarily followed by a rest penod CW1, and then applies a depolanzing pulse D1 14 to the battery of current amplitude IB to the battery The controller 13 waits for a predetermined period of time DW1 and measures an output voltage VI of the battery at a predetermined point in the rest period DW1 Controller 13 then applies another depolarizing pulse D2 of 5 current amplitude IB to the battery The controller again waits for a predetermined penod of time DW2 and measures another output voltage V2 of the battery at a corresponding predetermined point m the second rest penod DW2 It should be understood that the first output voltage measurement VI can be made in the beginning, middle, or end of the 10 first rest period DW1, so long as the subsequent output voltage measurement V2 is taken at the same relative point, relative to the beginning of the rest penod, in the next rest penod DW2 Decision 309 tests whether the difference (VI-V2) is greater than some maximum difference voltage (VDMAX) If not, then the 15 battery is not yet charged and the average charging current does not have to be adjusted In this case controller 13 will proceed to step 313 If VD>VDMAX, then the battery is being overcharged or is being charged at a rate greater than the battery can properly accept Therefore, in step 311 the controller 13 decreases the average charging 20 current Controller 13 then proceeds to step 313 In step 313 the controller 13 determines whether to terminate the pulse chargmg process The pulse chargmg cycle may be terminated for any one of several different reasons For example, the charging time set by the user may have expired, or the battery 25 temperature may be outside of an acceptable range, or the amplitude of the charging current IA may have been reduced to C/10 or less If a reason for termination of the pulse charging process has occurred then m step 315 the controller 13 will terminate the pulse charging urocess and will switch to another charging process, for 30 example, inckle charging if termination is because the charging current is C/10, or the controller 13 will stop the charging process entirely, for example, if termination is because time has expired or the temperature is unacceptable Also, a visual or audible indication of termination of the charge process may be provided to the operator 35 If, at step 313, controller 13 determines that the pulse charging process is not to be terminated then controller 13 will return to step 303 WO 97/03489 PCT/US96/11466 Figure 4 shows waveforms which illustrate a battery charging process and how the condition of the battel y is determined In this procedure, the open circuit battery voltage is measured at the beginning and at the end of the rest periods For convenience of 5 illustration, and not as a limitation, the voltage is shown as essentially constant during a rest penod However in practice, the voltage may vary dunng a rest penod and this provides further information as to the condition of the battery, especially for lead-acid and NiCd batteries If the voltage drops by more than a predetermined amount during a rest 10 period (VD1=V5-V6 and VD1>VD1MAX) then the electrolyte concentration is above normal and water should be added to the battery Audible and visual alarms may be used to alert the operator to this condition and the charging process may be automatically terminated Preferably, the measurements are made during the first rest period 15 DW1 Also, if the voltage measurements at the beginning and at the end of one rest penod (V5 and V6, respectively) are different by more than some predetermined amount (VD1=V5-V6 and VD1>VD2MAX), and the voltage measurements at the beginning and at 20 the end of a subsequent rest penod (V7 and V8, respectively, or V9 and V10, respectively) are also different by more than the predetermined amount (VD2=V7-V8 and VD2>VD2MAX), then this is an indication that the battery is not properly accepting the charge and therefore the charging process should be terminated 25 Figure 5 is a flow chart illustrating a vanation of the process of determining the condition of the battery The process of Figure 5 is identical to the process of Figure 3 except that step 503 replaces step 303, and decision 513 provides an explanation of some of the termination steps of decision 313 In step 513, additional voltage 30 measurements V5, V6, V7, and V8 are taken, and voltage differences VD1 and VD2 are determined In decision 513A, the controller 13 determines whether the voltage difference VD1 is greater than a predetermined maximum difference VD1MAX If so, then in step 513B the controller 13 initiates 35 an alarm to signal the operator to add water to the battery and then preferably terminates the charging process If not, then in decision 513C the controller detenmnes whether VD1 is greater than a m WO 97/03489 PCT/US96/11466 16 predetermined maximum VD2MAX and VD2 is also greater than VD2MAX If both conditions are met then the controller 13 terminates the charging process The controller 13 may also signal the operator of the termination If not then the controller 13 returns to step 503 5 In the present invention, as described above, the charging current may be adjusted by adjusting IA, by adiusting the duration of the charging pulse, by adjusting the repetition rate of the charging pulses, by adjusting the number or the duration of the depolarization pulses, or by adiusting the duration of one or more of the rest periods CW1, DW1, 10 DW2, etc Preferably, when the charging current is adjusted, the depolanzing cunent is adjusted similarly, such as by adjusting IB, by adjusting the duration of the depolarizing pulses, or by adjusting the number of depolanzing pulses between each charging pulse As an example of the above process, for a lead-acid sealed 15 battery with a 0 62 ampere-hour rating (C=0 62), IA is 2 4 amperes for 150 milliseconds, IB is 5 amperes for 2 milliseconds, and DW1 and DW2 are 12 milliseconds, and the repetition rate of the charge pulse (approximately 2 charge pulses per second) is such that the average charging current is 0 75 amperes (about 1 2C) CW1 may be used or 20 may not be present In this example, the pulse charging process will be terminated when the average charging current drops to 0 0623 amperes (0 1C) As another example, for a lead-acid sealed battery with a 52 ampere-hour rating (C=52), IA is 100 amperes and IB is 250 amperes, and the duration of the charge pulse is such that the average charging 25 current is 60 amperes (about 1 2C), and the pulse charging process will be terminated when the average charging current drops to 5 2 amperes (0 1C) Comparing the measured battery output voltage for consecutive rest periods after depolarizing pulses gives a better 30 indication of the state of charge than in the pnor art As a result, this method (1) allows charging the battery as rapidly as possible, (2) avoids heating of and damage to the battery which may occur with continued charging or overcharging, and (3) allows earlier termination or modification of the charging process without overcharging of the 35 battery Although it preferable to use the battery voltages measured dunng DW1 and DW2, the present invention is not so limited The battery voltages may be measured for any two consecutive or non- % WO 97/03489 PCT/US96/11466 17 consecutive discharge rest periods which are not separated by a charging pulse For example, DW2 and DW3 may be used, or DW1 and DW3 may be used Further, the depolarization pulses may have the same 5 amplitude or may have different amplitudes Likewise, the depolarization pulses may have the same duration or may have different durations In addition, the rest penods may have the same duration or may have different durations Although the present invention has been described with 10 particularity with respect to sealed lead-acid batteries, the present invention is not so limited The present invention is also useful for other types of batteries, for example, NiCd, NiMH, nickel-iron, nickel-zinc, silver-zinc, lithium-metal oxide, lithium ion-metal oxide, non-sealed lead-acid, etc It will be appreciated fiom the above that the present invention provides a method and an apparatus for rapidly charging a battery in a manner which does not cause overheating of the battery It will also be appreciated from the above that the present invention provides a method and an apparatus for charging a battery at a 20 rate that the battery can accept without damage The present invention also provides a method and an apparatus for determining the condition of a battery, including determining whether water should be added to the battery From a reading of the description above of the preferred 25 embodiment of the present invention, modifications and variations thereto may occur to those skilled in the art Therefore, the scope of the present invention is to be limited only by the claims below WO 97/03489 PCT/US96/11466 18

Claims (13)

1. Claims We claim 5 1 A method for charging a battery, comprising the steps of applying a charging pulse which provides an average charging current, applying a first depolanzing pulse, 10 waiting for a first rest penod, measunng the voltage of said battery at a predetermined point within said first rest penod, applying a second depolarizing pulse, waiting for a second rest penod, 15 measunng the voltage of said battery at said predetermined point within said second rest penod, determining a difference between said voltage at said predetermined point within said first rest penod and said voltage at said predetermined point within said second rest penod, and 20 if said difference is greater than a predetermined threshold then decreasing said average charging current

2. 2 The mecnod of Claim 1 and further comprising the step of repeating said steps of applying said charging pulse, applying said 25 first and second depolanzing pulses, waiting for said first and second rest penods, and measunng said voltages within said first and second rest penods WO 97/03489 PCT/US96/11466 19

3. 3 A method for charging a battery, comprising the steps of applying a charging pulse which provides an average charging current, 5 applying a first depolanzing pulse, waiting for a first rest penod, measunng the voltage of said battery at a predetermined point within said fust rest penod, applymg a second depolanzing pulse, 10 waiting for a second rest penod, applying a subsequent depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point within said subsequent rest penod, 15 determining a difference between said voltage at said predetermined point within said first rest penod and said voltage at said predetermined point within said subsequent rest penod, and if said difference is greater than a predetermined threshold then decreasing said average charging current 20

4. 4 The method of Claims 1 or 3 wherein said charging pulse has a charging pulse duration and said step of decreasing said average charging current comprises decreasing said charging pulse duration 25

5. 5 The method of Claims 1 or 3 wherein said charging pulse has a charging pulse current amplitude and said step of decreasing said average charging current compnses decreasing said charging pulse current amplitude 30

6. 6 The method of Claims 1 or 3 wherein said charging pulse has a charging pulse repetition rate and said step of decreasing said average charging current comprises decreasing said charging pulse repetition rate WO 97/03489 PCT/US96/11466

7. 7 The method of Claims 1 oi 3 wherein each said depolarizing pulse has a depolarizing pulse current amplitude and wherein said method further comprises the step of decreasing said depolanzing pulse current amplitude when said average charging current 5 is decreased

8. 8 The method of Claims 1 or 3 wherein each said depolanzing pulse has a depolanzing pulse duration and wherein said method further compnses the step of decreasmg said depolanzing pulse 10 duration when said average charging cunent is decreased

9. 9 The method of Claims 1 or 3 wherein a number of said depolarizing pulses follows each said charging pulse and wherein said method further compnses the step of decreasing said number of said 15 depolanzing pulses when said average charging current is decreased

10. 10 The method of Claims 1 or 3 wherein each said depolanzing pulse has a depolanzing pulse duration and wherein said step of decreasing said average charging current compnses increasing 20 said depolanzing pulse duration

11. 11 The method of Claims 1 or 3 wherein each said rest period has a rest penod duration and wherein said step of decreasing said average charging current comprises increasing said rest period 25 duration

12. 12 The method of Claims 1 or 3 wherein each said charging pulse is followed by a number of depolanzation pulses, and wherein said step of decreasing said averaging charging current 30 compnses increasing said number of depolanzation pulses WO 97/03489 PCT/US96/11466 21

13. 13 A method for charging a battery by a pulse charging process, comprising the steps of applying a charging pulse, applying a first depolanzing pulse, waiting for a first rest penod, measunng the voltage of said battery at a predetermined point within said first rest penod, applying a second depolanzing pulse, waiting for a second rest penod, measunng the voltage of said battery at said predetermined point within said second rest penod, determining a difference between said voltage at said predetermined point within said first rest penod and said voltage at said piedetenmned point within said second rest penod, and if said difference is greater than a predetermined threshold then terminating said pulse charging process ] 4 A method for determining the condition of a battery, compnsmg the steps of applying a charging pulse to said battery, applying a first depolarizing pulse to said battery, waiting for a first rest penod, measuring the voltage of said battery at a first predetermined point withm said first rest penod, measuring the voltage of said battery at a second predetermined point within said first rest penod, applying a second depolarizing pulse to said battery, waiting for a second rest period, determining a difference between said voltage at said first predetermined pomt and said voltage at said second predetermined point, and if said difference is greater than a predetermined threshold then indicating that water should be added to Suivi i>a\.vciy WO 97/03489 PCT/US96/11466 15 A method for terminating the charging process for a battery composing the steps of applying a chargmg pulse to said battery, applying a first depolanzing pulse to said baftery, 5 waiting for a first rest penod, measuring the voltage of said battery at a first predetermined point within said first rest penod, measuring the voltage of said battery at a second predetermined point within said first rest penod, 10 applying a second depolanzing pulse to said battery, waiting for a second rest penod, measuring the voltage of said battery at a first predetermined point within said second rest penod, measuring the voltage of said battery at a second 15 predetermined point within said second rest period, determining a first difference between said voltage at said first predetermined point within said first rest period and said voltage at said second predetermined point within said first rest penod, determining a second difference between said voltage at said 20 first predetermined point within said second rest penod and said voltage at said second predetermined point within said second rest period, and if both said first difference is greater than a predetermined threshold and said second difference is greater than said predetermined threshold then terminating said charging process 16 A method for charging a batteiy, comprising the steps of applying a charging pulse which provides a charging current, applying a depolanzing pulse which provides a depolanzing current, waiting for a rest penod, measunng the voltage of said battery at a predetermined point withm said rest penod, applying a subsequent depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point withm said subsequent rest penod, determining a difference between said voltage at said predetermined point within said rest penod and said voltage at said predetermined point within said subsequent rest penod, and if said difference is greater than a predetermined threshold then increasing said depolanzing current 17 A method for chargmg a battery, compnsing the steps of applying a charging pulse wmch provides a charging current, waiting for a first rest penod, measunng the voltage of said battery at a predetermined point withm said first rest penod, applying a depolanzing pulse which provides a depolanzing cunent, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point within said subsequent rest penod, determining a difference between said voltage at said predetermined point withm said first rest penod and said voltage at said predetermined point withm said subsequent rest penod, and if said difference is greater than a predetermined threshold then performing at least one of the following steps decreasing said charging current, increasing said depolanzing current, terminating said charging of said battery 18 A method for charging a cattery, compnsing the steps of applying a charging pulse which provides a charging current, applying a depolanzing pulse which provides a depolanzing current, waiting for a rest penod, measunng the voltage of said battery at a first predetermined point withm said rest penod, measunng the voltage of said battery at a second predetermined po int within said rest penod, applymg a subsequent depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined pomt within said subsequent rest penod, measunng the voltage of said battery at a second predetermined point withm said subsequent rest penod, determining a first difference between said voltage at said first predetermined point within s.md rest penod and said voltage at said second predetermined point within said rest penod, 2 c APR 1929 R_E 0 f~ I v L U 24 r) determining a second difference between said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point within said subsequent rest penod; and if both said first difference is greater than a predetermined threshold and said second difference is greater than said predetermined threshold then performing at least one of the following steps decreasing said charging current, increasing said depolanzing current 19 A method for charging a battery, compnsing the steps of applying a charging pulse which provides a charging current, waiting for a first rest penod, measunng the voltage of said battery at a first predetermined point withm said first rest penod, measunng the voltage of said battery at a second predetermined point withm said fust rest penod, applying a depolanzing pulse which provides a depolanzing current, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined pomt withm said subsequent rest penod, measunng the voltage of said battery at a second predetermined point withm said subsequent rest penod, determining a first difference between said voltage at said first predetermined point within said first rest penod and said voltage at said second predetermined point withm said first rest penod, determining asecond differencebetween said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point within said subsequent rest penod, and if both said first difference is greater than a predetermined threshold and said second difference is greater than said predetermined threshold then performing at least one of the following steps decreasing said charging current, increasing said depolanzing current, terminating said charging of said battery 20 The method of Claim 16, 17, 18, or 19 wherein a said depolarizing pulse has a depolanzing pulse current amplitude and wherein said step of increasing said depolanzing current compnses increasing said depolanzing pulse current amplitude 21 The method of Claim 16, 17, IS, or 19 wherein a said depolanzing pulse has a depolanzing pulse duration and wherein said step of increasing said depolanzing current compnses increasing said depolarizing pulse duration 22 The method of Claim 16,17,18, or 19 wherein a number of said depolanzing pulses follows said charging pulse and wherein said step of increasing said depolanzing current compnses increasing said number of said depolanzing pulses 22 APR 1BS9 RECEIVED 23 The method of Claim 16 or 17 and further compnsing repeating said steps until said difference is greater than said predetermined threshold 24 The method of Claim 18 or 19 and further compnsing repeating said steps until both said first difference is greater than said predetermined threshold and said second difference is greater than said predetermined threshold 25 The method of Claim 17,18, or 19 wherein said charging pulse has a chargmg pulse duration and said step of decreasmg said charging current compns es decreasing said charging pulse duration 26 The method of Claim 17,18, or 19 wherein said charging pulse has a charging pulse current amplitude and said step of decreasing said charging current compnses decreasing said charging pulse current amplitude 27 The method of Claim 17,18, or 19 wherein said charging pulse has a charging pulse repetition rate and said step of decreasmg said charging current compnses decreasmg said charging pulse repetition rate 28 The method of Claim 17, 18, or 19 wherem a said depolanzing pulse has a depolanzing pulse current amplitude and wherein said method further comprises the step of decreasing said depolanzing pulse current amplitude when said charging current is decreased 29 The method of Claim 17, 18, or 19 wherein a said depolanzing pulse has a depolarizing pulse duration and wherein said method further comprises the step of decreasing said depolanzing pulse duration when said charging current is decreased 30 The method of Claim 17, 18, or 19 v'herein a number of said depolanzing pulses follows each said chargmg pulse and wherein said method further compnses the step of decreasing said number of said depolanzing pulses when said charging current is decreased 31 The method of Claim 16,17,18,or 19 wherem each said rest penod has a rest penod duration and wherem said step of decreasing said chargmg current compnses increasing said rest penod duration 32 The method of Claim 17,18, or 19 wherein a said charging pulse is followed by a number of depolanzation pulses, and wherein said step of decreasing said charging current composes increasing said number of depolarization pulses 33 An apparatus foi chargmg a battery, compnsing a charging circuit for applying a chargmg pulse which provides a charging current to said battery, a discharging circuit for applying a depolanzing pulse to said battery, said depolanzing pulse having a depolanzing pulse current amplitude and a depolanzing pulse duration, and a controller functionally connected to said charging circuit and to said discharging circuit for I ' I i _ ZX APR M _ RECEIVCD controlling said charging circuit and said discharging circuit m accordance v/ith at least one of the following procedures (a) causing said charging circuit to apply a charging pulse, causing said discharging circuit to apply a depolanzing pulse, waiting for a rest penod, measunng the voltage of said battery at a predetermined point within said rest period, causing said discharging circuit to apply a subsequent depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point withm said subsequent rest penod, determining a difference between said voltage at said predetermined pomt withm said rest penod and said voltage at said predetermined pomt within said subsequent rest penod, and increasing said depolanzing current in response to said diffeience being greater than a predetermined threshold, (b) causing said chargmg circuit to apply a charging pulse, waiting for a first rest penod, measunng the voltage of said battery at a predetermined point within said first rest penod, causing said discharging circuit to apply a depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point within said subsequent rest penod, determining a difference between said voltage at said predetermined point within said first rest penod and said voltage at said predetermined point withm said subsequent rest penod, and decreasing said charging current in response to said difference being greater than a predetermined threshold, (c) causing said charging circuit to apply a charging pulse, waiting for a first rest penod, measunng the voltage of said battery at a predetermined pomt withm said first rest penod, causing said discharging circuit to apply a depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at said predetermined point within said subsequent rest penod, determining a difference between said voltage at said predetermined point withm said first rest penod and said voltage at said predetermined point within said subsequent rest penod, and increasing said depolanzing current in response to said difference being greater than a predetermined threshold, (d) causing said charging circuit to apply a charging pulse, waiting for a first rest penod, measunng the voltage of said battery at a predetermined point within said first rest penod, causing said discharging circuit to apply a depolanzing pulse, waiting for a subsequent rest period, measunng the voltage of said battery at said predetenmned point withm said i ( i 'j Zc APR 1999 R L C t I v L D 27 V ■ ^ 1 ! ( , subsequent rest penod, determining a difference between said voltage at said predetermined point within said first rest penod and said voltage at said predetermined pomt wuhm said subsequent rest penod, and terminating said charging of said battery in response to said difference being greater than a predetermined threshold, (e) causing said charging circuit to apply a charging pulse, causing said discharging circuit to apply a depolanzing pulse, waiting for a rest penod, measunng the voltage of said battery at a first predetermined point within said rest penod, penod, measunng the voltage of said battery at a second predetermined point withm said rest causing said discharging circuit to apply a subsequent depolanzing pulse, waiting for a subsequent rest period, measunng the voltage of said battery at a first predetermined point withm said subsequent rest penod, measunng the voltage of said battery at a second predetermined point within said subsequent rest penod, determining a first difference between said voltage at said first predetermined point withm said rest penod and said voltage at said second predetemuned point within said rest penod, determining a second difference between said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point within said subsequent rest penod, and decreasing said charging current m response to both said first difference being greater than a predetermined threshold and said second difference being greater than said predetermined threshold, (f) causing said charging circuit to apply a chargmg pulse, causing said discharging circuit to apply a depolanzing pulse, waiting for a rest penod, measunng the voltage of said battery at a first predetermined point withm said rest penod, penod, measuring the voltage of said battery at a second predetermined point within said rest causing said discharging circuit to apply a subsequent depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined point withm said subsequent rest penod, measunng the voltage of said battery at a second predetermined pomt wuhm said subsequent rest penod, determining a first difference between said voltage at said fiist predetermined point withm said rest penod and said voltage at said second predetermined point withm said rest penod, determining asecond difference between said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point withm said subsequent rest penod, and increasing said depolanzing current in response to both Said first difference being j 2- APR iyC9 L R t C L- I V (- D greater than a predetermined threshold and said second difference being greater than said predetermined threshold; (g) causing said charging circuit to apply a charging pulse, waiting for a first rest penod, measunng the voltage of said battery at a first predetermined pomt withm said first rest penod, measunng the voltage of said battery at a second predetermined point within said first rest penod, causing said discharging circuit to apply a depolanzing pulse which provides a depolanzing current, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined point withm said subsequent rest penod, measunng the voltage of said battery at a second predetermined point withm said subsequent rest penod, determining a first difference between said voltage at said first predetermined point within said first rest penod and said voltage at said second predetermined pomt within said first rest penod, determining a second difference between said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point withm said subsequent rest penod, and decreasing said charging current in response to both said first difference being greater than a predetermined threshold and said second difference being greater than said predetermined threshold, (h) causing said chargmg circuit to apply a charging pulse, waiting for a first rest penod, measuring the voltage of said battery at a first predetermined pomt withm said first rest penod, measunng the voltage of said battery at a second predetermined point within said first rest penod, causing said discharging circuit to apply a depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined point withm said subsequent rest penod, measunng the voltage of said battery at a second predetermined point withm said subsequent rest penod, determining a first difference between said voltage at said first predetermined point withm said first rest penod and said voltage at said second predetermined point within said first rest penod, determining a second difference between said voltage at said first predetermined point withm said subsequent rest penod and said voltage at said second predetermined point withm said subsequent rest penod, and increasing said depolanzing current m response to both said first difference being greater than a predetermined threshold and said second difference being greater than said predetermined threshold, ! ( L *■ ' - u 2'a APR 1939 R L C 11 : Li 29 t f causing said charging circuit to apply a charging pulse, waiting for a first rest penod, measunng the voltage of said battery at a first predetermined point within said first measunng the voltage of said battery at a second predetermined point withm said first causing said discharging circuit to apply a depolanzing pulse, waiting for a subsequent rest penod, measunng the voltage of said battery at a first predetermined point within said subsequent rest penod, measunng the voltage of said battery at a second predetermined point within said subsequent rest penod, determining a first difference between said voltage at said first predetermined point within said first rest penod and said voltage at said second predetermined pomt within said first rest penod, determining a second difference between said voltage at said first predetermined point within said subsequent rest penod and said voltage at said second predetermined point within said subsequent rest penod, and terminating said charging of said battery in response to both said first difference being greater than a predetermined threshold and said second difference being greater than said predetermined threshold 34 The apparatus of Claim 33 wherem said controller is further responsive to said difference being greater than said predetermined threshold for decreasing said charging pulse duration. 35 The apparatus of Claim 33 wherein said controller is further responsive to said difference being greater than said predetermined threshold for decreasing said charging pulse current amplitude 36 The apparatus of Cla.m 33 wherein said chargmg pulse has a charging pulse repetition rate and wherein said controller is further responsive to said difference being greater than said predetermined threshold for decreasing said average chargmg current compnses decreasmg said charging pulse repetition rate 37 The apparatus of Claim 33 wherein said controller is further responsive to said difference being greater than said predetermined threshold for decreasing said depolanzing pulse current amplitude 38 The apparatus of Claim 33 wherein said controller is further responsive to said difference being greater than said predetermined threshold for decreasing said depolanzing pulse duration 39 The apparatus of Claim 33 wherein a number of said depolanzing pulses follows each said charging pulse and wherein said controller is further responsive to said difference being greater APR ra Received « rest penod, rest penod, 30 I than said predetermined threshold for decreasing said number of said depolanzing pulses when said average charging current is decreased 40 The apparatus of Claim 33 wherein a said depolarizing pulse has a depolanzing pulse duration and wherein said controller is further responsive to said difference being greater than said predetermined threshold for increasing said depolanzing pulse duration 41 The apparatus of Claim 33 wherein each said rest penod has a rest penod duration and wherein said controller is further responsive to said difference being greater than said predetermined threshold for increasing said rest penod duration 42 The apparatus of Claim 33 wherein a said charging pulse is followed by a number of depolanzation pulses and wherein said controller is furthei responsive to said difference being greater than said predetermined threshold for increasing said number of depolanzation pulses 43 The apparatus of Claim 33 wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for decreasing said charging pulse duration 44 Hie apparatus of Claim 33 wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold foi decreasing said charging pulse current amplitude 45 The apparatus of Claim 33 wherein said charging pulse has a charging pulse repetition rate and wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for decreasing said average charging current compnses decreasmg said charging pulse repetition rate 46 The apparatus of Claim 33 wherein said controller is further responsive to both said first d.ffercnce aid said second difference being greater than said predetermined threshold for decreasing said depolanzing pulse current amplitude 47 The apparatus of Claim 33 wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for decreasing said depolanzing pulse duration 48 The apparatus of Claim 33 wherein a number of said depolanzing pulses follows each said charging pulse and wherein said controller is further response e to both said first difference and said sccond difference being greater than said predetermined threshold for decreasing said number of said depolanzing pulses when said average charging current is decreased 49 The apparatus of Claim 33 wherein a said depolanzing pulse has a depolanzing pulse duration and wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for increasing said depolanzing pulse duration 22 APR 1839 fl EC El V t U 31 50 The apparatus of Claim 33 wherein each said rest penod has a rest penod duration and wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for increasing said rest penod duration 51 The apparatus of Claim 33 wherem a said charging pulse is followed by a number of depolanzation pulses and wherein said controller is further responsive to both said first difference and said second difference being greater than said predetermined threshold for increasing said number of depolanzation pulses 52 A method for charging a battery substantially as described herein with reference to Figures 2A-2B or Figure 4 of the drawings 53 A method for terminating the charging process for a battery substantially as described herein with reference to Figures 2A-2B or Figure 4 of the drawings 54 A method for determining the condition of a battery substantially as described herein with reference to Figures 3, 4 or 5 of the drawings 55 An apparatus for charging a battery substantially as herein described with reference to Figure 1 of the drawings 22 APR 1929 E 0 £ 1 v t o