Abstract:
A battery charger system providing increased reliability over conventional chargers includes one or more charging modules coupled to a central controller module. Each charging module is cable of charging one or two batteries and includes control logic that controls the charging current provided to each battery. Each charging module is capable of charging the associated batteries using a pre-programmed, selectable charging protocol. The control logic included in each of the charging module provides a “first level of intelligence” for charging batteries. The controller module provides a “second level of intelligence” that generally operates in conjunction with the first level of intelligence provided by the charging modules. The second level of intelligence provided by the controller module individually enables and disables charging to a particular battery by an associated charging module. The charging modules are capable of charging batteries even without control from the second level of intelligence. Thus, reliability is increased by being able to continue battery charging even if the controller module fails or is removed from the battery charging system. Other features such as the lack of battery voltage sense lines removes the possibility of failure due to faulty or damaged sense lines, thereby increasing reliability.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a battery charger. More particularly, the invention relates to a modular battery charger system with charging control distributed among various modules. Still more particularly, the invention relates to a modular charger system with improved reliability and employing an improved method for determining a fully charged battery. 
     2. Background of the Invention 
     Although rechargeable batteries and battery rechargers have been available for years, significant room for improvement remains in this technology. Some rechargeable batteries are used in non-benign, outdoor environments. For example, land-based seismic survey equipment typically employs rechargeable batteries to power the data acquisition units used to acquire seismic data. These batteries, like all rechargeable batteries, must be recharged periodically. Normally, the batteries are removed from the equipment and connected to rechargers which are transported to the site being seismically surveyed. For some surveys it may be preferable to leave the recharging equipment in the field rather than transporting it to the field each time the batteries need charging. 
     As such, the rechargers are operated in an outdoor environment which often is harsh to the electronics comprising the recharger. The environment may include conditions such as high humidity, high or low temperature, rain, snow, or sleet. Such environmental conditions increase the likelihood of a failure in the charger. Field-based battery chargers typically are constructed to minimize the risk of the internal components becoming ruined from moisture and also to reduce damage to the unit occasioned by falling tree limbs, mishandling by field personnel and other factors. Although being able to easily maintain the recharger is important, conventional chargers are constructed more for durability than maintainability. That is, servicing such chargers usually is difficult to perform in the field. Thus, when a conventional charger fails, a technician is sent into the field to examine and, if possible, repair the unit. Often, however, the technician is forced to return the unit to a well-equipped, indoor service facility to make the repair, a procedure which is time consuming and costly. 
     Some field-based battery chargers are capable of charging more than one battery at a time. Such chargers usually have multiple charging circuits, each circuit capable of charging a single battery. Typically, if just one of the charging circuits in such a charger fails, the entire charger, including the remaining fully functional charging circuits, may have to be transported to a service facility to repair or replace the one malfunctioning circuit. Thus, because of one malfunctioning charging circuit, the entire charging capability of the charger is lost until the repair is completed. Accordingly, it would be desirable have a battery charger that, is highly reliable, and also can be repaired without losing the full charging capability of the unit while the failure is being corrected. 
     The desire for increased reliability also applies to battery chargers that are used indoors in a more benign environment where the possibility of a malfunction still exists. In many indoor applications, battery chargers may be used in time critical events such as related to the use of medical equipment in a hospital in which battery and battery charger “down time” should be minimized. 
     Another aspect of reliable battery charging involves determining when a battery has been fully charged. Determining the “end of charge” condition prevents a battery from being over-charged, a condition that can damage certain types of rechargeable batteries. Many conventional end of charge determinations are based on measuring the voltage of the battery and determining when the voltage meets or exceeds a predetermined threshold. Often, such voltage-based end of charge protocols are inaccurate because of a particular battery&#39;s chemistry. Such inaccuracies may cause a battery to be under-charged (i.e., not be fully charged) or be over-charged to a certain extent. Thus, a more accurate, reliable method for determining the end of charge condition is needed. 
     Accordingly, it would be desirable to have a battery charger that provides greater reliability and maintainability than with conventional chargers and can more precisely charge a battery to full capacity. Despite the advantages that such a charger would offer, to date no such charger has been introduced. 
     BRIEF SUMMARY OF THE INVENTION 
     The deficiencies of the prior art described above are solved in large part by a battery charger system that provides increased reliability over conventional chargers. The charging system includes one or more charging modules coupled to a central controller module. Each charging module operates independently of, and is unaffected by, other charging modules. In this manner, reliability of the overall charging system is increased because a failure of one charging module does not affect the charging capability of other charging modules. 
     Electrical power for charging the batteries and driving the electronics internal to the charging and controller modules preferably is provided by a 24 VDC power supply. Each charging module is cable of charging one or more batteries and includes control logic that separately controls the charging current provided to each battery. Each charging module is capable of charging the associated batteries using a pre-programmed, selectable charging protocol. The control logic included in any each charging module provides a “first level of intelligence” for charging batteries. The first level of intelligence generally selects various stages of charging and discontinues charging when the battery is fully charged. 
     The controller module provides a “second level of intelligence” that generally operates in conjunction with the first level of intelligence provided by the discrete charging modules. The second level of intelligence provided by the controller module enables and disables charging to an individual battery by asserting an inhibit signal to the charging module associated with the targeted battery. Disabling battery charging may be desired as a result of detecting a fully charged battery or detecting fault conditions such as over voltage, over current, out of range temperature, or leakage current. Disabling battery charging also may be desired as a result of detecting faulty batteries by monitoring rate of voltage, current and temperature changes within the charging battery. The charging modules advantageously are capable of charging batteries even without control from the second level of intelligence. Thus, reliability also is increased by being able to continue battery charging even if the controller module fails or is removed from the battery charging system. 
     Other factors contribute to the increased reliability of the preferred battery charging system. For example, the present battery charging system does not require a pair of sense lines connecting the battery terminals to the charging module as is typical for conventional battery chargers. Sense lines of conventional chargers permit those chargers to determine the actual voltage of the battery without the voltage drop associated with battery cables. The charging modules of the preferred embodiment include a resistor which develops a voltage indicative of the current through the battery and that voltage is used by the control logic in each charger module to compensate for battery cable voltage drop during charging. 
     The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention can be obtained when the following detailed description of the preferred embodiments is considered in conjunction with the following drawings, in which: 
     FIGS. 1A through 1C show a block diagram of a battery charger system constructed in accordance with the preferred embodiment of the invention and including a power supply, one or more charger modules and a controller module; 
     FIGS. 2A-1 through  2 A- 4 , FIGS. 2B-1 through  2 B- 4 , and FIGS. 2C-1 through  2 C- 9  are schematic diagrams of the charger modules of FIG. 1; and 
     FIGS. 3A-1 through  3 A- 9  and FIGS. 3B-1 through  3 B- 6  are schematic diagrams of the controller module of FIG.  1 . 
    
    
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, components may be referred to by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, which is comprised of three subfigures entitled FIGS. 1A,  1 B and  1 C, a battery charger system  100  constructed in accordance with the preferred embodiment generally includes a power supply unit  110  (FIG.  1 A), one or more charger modules  200  (FIGS.  1 A &amp;  1 B), and a controller module  400  (FIG.  1 C). If desired, a terminal  500  (FIG. 1C) or other type of communication device also may be coupled to the controller module  400  to permit remote control and status checking of the charger system  100 . Although the battery charger system  100  can be configured to charge any type of battery, the preferred embodiment of the system charges lead-acid batteries which generally are preferred for seismic data acquisition applications. 
     Each charger module  200  receives electrical power from the power supply unit  110  and, as shown, can charge one or two rechargeable batteries connected to the ports labeled “Batt Port  1 ,” “Batt Port  2 ,” and so on. Each charger module  200  communicates with the controller module  400  preferably through serial lines coupling each charger module  200  independently to the controller module  400 . Each charger module  200  includes a serial interface and analog/digital (A/D) circuit  280  (FIGS. 1A &amp; 1B) and other components best shown in FIGS.  2 A- 2 C. The controller module  400  includes a RS 422  line driver circuit  480  (FIG. 1C) to provide serial interfaces to each of the charger modules  200 . 
     In accordance with the preferred embodiment, each charger module  200  includes a Pulse Width Modulator (PWM) Port A and a Pulse Width Modulator (PWM) Port B. Both PWM ports include substantially identical circuitry for charging batteries coupled thereto. 
     Further, each charger module  200  preferably functions independently from the other charger modules in the battery charger system  100 . For example, one charger module  200  can charge a battery while another charger module  200  has been disabled by controller module  400 . 
     Additionally, each charger module  200  preferably is constructed as a physically separate unit or assembly from the other charger modules so that a single charger module  200  can physically be removed from the battery charger system  100  without removing or disturbing the operation of any of the other charger modules  200 . As such, a housing (not shown) containing the charger module  200  is designed so as to permit access to each individual charger module  200 . Further, a charger module  200  can be removed while other charger modules  200  are charging batteries. Removing one charger module  200  does not effect other charger modules  200  because each charger module  200  communicates separately with the controller module  400  and receives power via an independent power feed from the power supply unit  110 . This feature permits charger modules  200  to be “hot swappable” which means a charger module  200  can be removed and replaced without having to turn off the entire charger system  100 . Other functional charger modules can continue to charge their batteries when a particular charger module is being replaced. Accordingly, if it is suspected or determined that a particular charger module  200  is defective and requires maintenance or replacement, just that particular charger module  200  is removed from the charger  100  and repaired and/or replaced by a new module. 
     Being able to “hot swap” individual charger module  200  improves ease of maintenance of the battery charger system  100  over conventional charging systems. The entire battery charger system  100  need not be transported to a service center which would involve a significant cost. Instead, a single charger module  200  can be sent into the field and a repair technician can quickly and easily replace a defective charger module. Maintenance costs are reduced and the entire battery charging capacity of the charger  100  is not disabled while maintenance of a single charger module is performed. 
     The battery charger system  100  shown in FIG. 1 provides a significant advance in reliability over conventional battery chargers. In accordance with the preferred embodiment and explained in greater detail with respect to FIGS.  2 A-C and  3 A-B, battery charger system  100  implements two levels of “intelligence.” Each level of intelligence is capable of asserting a predetermined level of control over the charging of each battery. Each PWM port preferably includes a “first level of intelligence” (described below) for controlling battery charging. The control module  400  implements a “second level of intelligence” and generally functions in conjunction with the first level of intelligence implemented in the charger modules  200 . 
     Normally, the first level of intelligence implemented in each charger module  200  provides the primary control over battery charging. As such, each charger module is capable of controlling the amount of charging current provided to a battery. The second level of intelligence implemented in the control module  400  receives various parameters from each PWM port over the serial interface between the charger module  200  and control module  400  and enables and disables charging to each port individually. The parameters may include any suitable value such as battery voltage, current, temperature, and pressure. The control module  400  monitors or processes these parameters and turns on and off charging to a particular battery as necessary. For example, the control module may disable charging to a particular battery upon detection of an overvoltage or out of range temperature condition. 
     The charging system  100  can charge batteries even without the second level of intelligence provided by the control module  400 . Further, the second level of intelligence can be used with respect to certain desired charger modules  400 , but not others. Thus, some charger modules  200  or PWM ports can be controlled by the second level of intelligence provided by the control module  400  while other charger modules  200  or PWM ports charge batteries according to only their first level of intelligence. 
     Referring still to FIG. 1, the power supply unit  110  preferably includes a universal voltage/power factor correction module  120  (FIG. 1A) coupled to one or more DC—DC converters  130  (FIG.  1 A). The universal voltage/power factor correction module  120  preferably includes a line filter (not shown), such as an 07818 Ham filter manufactured by Vicor and a power factor correction (PFC) module (not shown), such as a VI-HAM-CP 600 watt PFC module also manufactured by Vicor. The line filter attenuates noise from the line voltage which preferably includes an AC (alternating current) voltage in range from about 85 to 265 VAC. The PFC module provides power factor correction to the incoming line voltage and converts the AC line voltage to a DC voltage. The universal voltage/power factor correction module  120  thus provides filtering, power factor correction and can be configured to provide other desired power conditioning functions. Both the filter and PFC module are well known, commercially available components. 
     The DC—DC converters  130  include any suitable converter for changing the DC voltage provided from the PFC module included in the universal voltage/power factor correction module  120  to a lower DC voltage that is usable by the charger modules  200  and controller module  400 . As shown, power supply unit  110  includes three DC—DC converters  130  although the number of converters may vary depending on the number of charger modules  200  included in the battery charger system  100 . The DC—DC converters preferably include any suitable converter such as the VI-263-CU which is a 250 VDC-to-24 VDC step down, 200 watt supply module manufactured by Vicor. Because these particular Vicor DC—DC converters  130  are rated only for 200 watts, each DC—DC converter generally is capable of only providing power to two charger modules. Further, because the exemplary embodiment of FIG. 1 includes six charger modules  200 , the power supply unit  110  includes three DC—DC converters  130 . One of the DC—DC converters  130  also provides power to the controller module  400 . Each charger module  200  and controller module  400  includes a 24 VDC input circuit  202  (FIGS. 1A &amp; 1B) and  402  (FIG.  1 C), respectively, to condition the 24 VDC power feed from the power supply unit  110 . 
     Referring now to FIGS.  2 A- 2 C a preferred circuit schematic implementation of a dual PWM port, single charger module  200  is shown. FIG. 2A shows the schematic for one of the PWM ports and FIG. 2B includes the schematic for the other PWM port. FIGS. 2A and 2B are substantially identical and thus only FIG. 2A will be discussed. FIG. 2C generally includes the serial interface control and A/D  280  along with one or more status light emitting diodes (LED&#39;s)  288  and associated circuitry. The component part numbers and values shown in the FIGS.  2 A- 2 C, as well as in FIGS.  3 A- 3 B (discussed below), are exemplary only of one embodiment of the invention. Upon reading the following discussion of the schematics, one of ordinary skill in the art will appreciate that there are many other component values and parts that can be used besides the values and parts shown in the Figures. Further, the circuit topologies shown can be changed in any suitable matter yet still implement the principles and functions discussed herein. 
     Referring now to FIG. 2A, which is comprised of four subfigures entitled FIGS. 2A-1 through  2 A- 4 , charger module  200  includes a 24 VDC input circuit  202  (FIG. 2A-2 and a portion of which is also shown in FIG.  2 C- 4 ), an inhibit circuit  204  (FIG.  2 A- 1 ), a voltage monitor circuit  206  (FIG.  2 A- 2 ), an inductor coil  210  (FIG.  2 A- 2 ), a leakage detection circuit  212  (FIG.  2 A- 4 ), a current monitor circuit  216  (FIG.  2 A- 3 ), a charge control integrated circuit (IC)  220  (FIG.  2 A- 1 ), and other components as shown. The charge control IC  220  preferably is the lead-acid fast-charge IC bq2031 manufactured by Benchmarq, although any other suitable charge control IC could be used as well. 
     Connector J 101  is used for connection to the rechargeable battery. The connector pin labeled L couples to the positive terminal of the battery and the pin labeled K couples to the battery negative terminal. Pins M, N, P, and R preferably are tied together and coupled to the leakage detection circuit  212  and not the battery. Any current that is present on pins M, N, P, R represents undesirable leakage current and is detected by leakage detection circuit  212 . Generally, charge current is provided from the +24 VDC source provided by the power supply unit  110  and conditioned by 24 VDC input circuit  202  which comprises a low voltage drop Schottky diode D 1 , diode D 102  and capacitors C 27 , C 101 , C 102 , C 28 , and resistor R 101 . The charger module  200  preferably transmits an indication of the presence of leakage current to the controller module  400  which, in turn, may initiate signaling a user of the leakage condition or may shut off charging to the affected battery, thereby decreasing the potential for further harm to that battery and increasing overall system safety and reliability. 
     Node  203  (FIG. 2A-2) represents the connection point between the cathode terminal of Schottky diode D 1 , the non-grounded terminal of capacitors C 28 , C 102 , the cathode of diode D 102  and resistor R 123 . The charge current from the 24 VDC input circuit  202  flows from node  203  through field effect transistor (FET) Q 103 , through inductor coil  210  and to the positive terminal of the battery via pin L of connector J 101 . The current from the negative terminal of the battery returns via pin K of connector J 101  and through resistors R 28  and R 103  to ground. Resistors R 28  and R 103  preferably are 0.1 ohm resistors connected in parallel and function as current sensing resistors. As such, the voltage developed across these resistors in response to return current from the battery is proportional to the battery current. That voltage is amplified by operational amplifier U 103 C which is connected to resistors R 127  and R 128  in a non-inverting amplifier configuration. With resistor R 127 =93.1 kohms and R 128 =10 kohms, the gain is approximately 10.3. The output signal from operational amplifier U 103  is labeled CURRENT 0  and thus is a voltage that is proportional to the current through the battery. 
     Referring still to FIG. 2A, the battery voltage is scaled by a voltage divider network comprising resistors R 129  and R 130  which, given the component values for R 129  and R 130  shown in FIG. 2A, reduce the battery voltage to a value that is approximately 20% of the actual battery voltage. The scaled battery voltage is then provided to a high input impedance voltage follower buffer U 103 D. The output signal from U 103 D is labeled VOLTAGE 0  and thus represents a scaled down version of the battery voltage. The battery voltage could also be scaled up if desired by replacing the voltage divider network with an amplifier with a gain that is greater than 1. 
     The charger control IC  220  controls the amount of charging current provided to the battery from 24 VDC input circuit  202  by turning FET Q 103  on and off at a desired rate and with a desired duty cycle (i.e., the percentage of time the FET is on and conducting relative to the time it is off). In accordance with the presently preferred embodiment, charger control IC  220  is the bq2031 lead-acid fast-charge integrated circuit (IC) manufactured Benchmarq. The bq2031 IC  220  provides selectable charging algorithms including a two-step voltage with temperature compensated constant-voltage maintenance algorithm, a two-step current with constant-rate pulsed current maintenance, and pulsed current. These algorithms include multiple stages of charging and are controlled by the bq2031 IC  220 . The bq2031  220  provides the first level of intelligence noted above for charging the battery connected to JI 01 . As such, the bq2031  220  in conjunction with the other circuitry shown in FIG. 2A is capable of charging the battery without assistance from the control module  400 . A complete description of the Benchmarq bq2031 charging IC can be found in the data sheet associated with that part, Benchmarq bq2031 Lead-Acid Fast-Charge IC (April 1997), incorporated herein by reference. 
     In general, the battery voltage is provided to the charger module  220  via pin L of J 101  and resistors R 114  and R 110  to the battery (BAT) input pin (pin  3 ) of charge control IC  220 . The modulator (MOD) signal from pin  14  is a pulse-width modulated push/pull output signal that is used to control the charging current to the battery. The MOD output pin (pin  14 ) connects to the input pin (pin  2 ) of the high side gate driver U 102 . The high side gate drive U 102  boosts the 5 V peak-to-peak PWM signal from the MOD output pin to approximately 18 V peak-to-peak which is used to drive the gate of FET Q 103 . The output drive of U 102  also permits the 18 V PWM signal (pin  7 ) to rise up with the source voltage of FET Q 103  (pins  5  and  6  of U 102 ) to provide a consistent 18 V gate to source PWM signal to this type of FET circuit configuration. The high side gate driver U 102  also provides sufficient current to turn power FET Q 103  on and off. The MOD signal thus represents the current-switching control output signal from charge control IC  220 . The MOD signal switches high to enable current flow to the battery and low to inhibit current flow. 
     The charge control IC  220  controls charging by pulse-width modulation of the MOD output signal, and supports both constant-current and constant-voltage regulation. The charge control IC  220  monitors charging current by monitoring the voltage at the current sense (SNS) pin (pin  7 ), and charge voltage at the BAT pin. These voltages are compared to an internal temperature-compensated reference, and the MOD output signal is modulated to maintain the desired value of charge current. The battery current is sensed via a voltage developed on the SNS pin by resistor R 105 . 
     The switching frequency of the MOD output signal is specified by the value of capacitor C 112  connected between the TPWM pin (pin  9 ) and ground. Although the switching rate can be any rate within a range from about 10 kHz to about 200 kHz, a switching rate of 100 kHz is preferred and is set accordingly by making capacitor C 112  a nanofarad capacitor. To prevent oscillation in the voltage and current control loops, resistor R 118  and capacitors C 110  and C 111  are provided between the VCOMP and ICOMP input pins  4  and  5  which permit voltage loop and current loop stability, respectively. 
     The charger control IC  220  is cable of charging the battery in any one of a variety of selectable modes. Each charging mode is selected by asserting the QSEL and TSEL input signals on pins  10  and  15  of the charger control IC  220 . Table I identifies the various charging modes provided by the bq2031 and the QSEL and TSEL voltage levels necessary to select each mode. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Charger Control IC 220 Charging Mode Selection 
               
             
          
           
               
                   
                   
                   
                   
                 MOD 
               
               
                 Algorithm/State 
                 QSEL 
                 TSEL 
                 Conditions 
                 Output 
               
               
                   
               
               
                 Two-Step Voltage 
                 L 
                 H or L 
                   
                   
               
               
                 Fast charge, 
                   
                   
                 While 
                 Current 
               
               
                 phase 1 
                   
                   
                 VBAT &lt; VBLK, 
                 regulation 
               
               
                   
                   
                   
                 ISNS = IMAX 
               
               
                 Fast charge, 
                   
                   
                 While ISNS &gt; IMIN, 
                 Voltage 
               
               
                 phase 2 
                   
                   
                 VBAT = VBLK 
                 regulation 
               
               
                 Primary 
                   
                   
                 ISNS = IMIN 
               
               
                 termination 
               
               
                 Maintenance 
                   
                   
                 VBAT = VFLT 
                 Voltage 
               
               
                   
                   
                   
                   
                 regulation 
               
               
                 Two-Step Current 
                 H 
                 L 
               
               
                 Fast charge 
                   
                   
                 While 
                 Current 
               
               
                   
                   
                   
                 VBAT &lt; VBLK, 
                 regulation 
               
               
                   
                   
                   
                 ISNS = IMAX 
               
               
                 Primary 
                   
                   
                 VBAT = VBLK 
               
               
                 termination 
                   
                   
                 or Δ 2 V &lt;− 8 mV 
               
               
                 Maintenance 
                   
                   
                 ISNS pulsed to 
                 Fixed 
               
               
                   
                   
                   
                 average IFLT 
                 pulse 
               
               
                   
                   
                   
                   
                 current 
               
               
                 Pulsed Current 
                 H 
                 H 
               
               
                 Fast charge 
                   
                   
                 While 
                 Current 
               
               
                   
                   
                   
                 VBAT &lt; VBLK, 
                 regulation 
               
               
                   
                   
                   
                 ISNS = IMAX 
               
               
                 Primary 
                   
                   
                 VBAT = VBLK 
               
               
                 termination 
               
               
                 Maintenance 
                   
                   
                 ISNS = IMAX after 
                 Hysteretic 
               
               
                   
                   
                   
                 VBAT = VFLT; 
                 pulse 
               
               
                   
                   
                   
                 ISNS = 0 
                 current 
               
               
                   
                   
                   
                 after VBAT = VBLK 
               
               
                   
               
             
          
         
       
     
     As shown in FIG. 2A QSEL and TSEL signals are preset by jumpers JP 103  and JP 102 , but could be selectable by controller module  400  if desired. 
     Charging mode status is provided visually at the charger module  200  by LED  101 , LED  102  and LED  103  which are coupled to the QSEL, TSEL and DSEL LED output drive pins of charge control IC  200  by current limiting resistors R 108 , R 107 , and R 106 . These status LED&#39;s generally indicate what stage of charging the charge control IC  220  currently is performing as is described in the bq2031 data sheet. 
     The battery connector J 101  preferably includes one or more pins that are not connected to the battery and thus generally are unused. As shown in FIG. 2A, these pins are labeled M, N, P, and R. Any leakage current that may develop on the battery connector J 101  is detected by leakage detection circuit  212 . The leakage detection circuit  212  generally converts any current provided from any of the unused pins M, N, P, and/or R on connector J 101  to a voltage. Resistors R 42  and R 136  preferably comprise a current-to-voltage converter. The voltage developed across resistor R 136  is proportional to the leakage current from pins M, N, P, R. Operational amplifier U 104  preferably is configured as a high input impedance voltage follower, the output signal of which is labeled FLOAT 0 . Thus, FLOAT 0  is a voltage that is indicative of any leakage current that may happen to develop on the battery connector J 101 . 
     To accurately control charging current, it is important to determine the battery voltage at the battery terminals and not at the charger end of the cable that connects the battery to the charger. The voltage usually differs from one end of the battery cable to the other because of the inherent impedance of the battery cables which causes a voltage drop along the cable. Conventional battery chargers have solved this problem by including separate “sense” lines from the battery terminals to a high impedance voltage monitor circuit in the charger. These sense lines are in addition to the battery cable that provides charging current to the battery. Because the impedance of the voltage monitor is relatively high, negligible current flows through the sense lines and the voltage at the end of sense lines connected to the voltage monitor is substantially the same as the actual battery voltage. Sense lines are susceptible to breakage and thus cause reliability problems with conventional chargers. 
     Referring to FIG. 2C, which is comprised of nine subfigures entitled FIGS. 2C-1 through  2 C- 9 , the serial interface control and A/D logic  280  (FIG. 2C-1) and status LED&#39;s  288  (FIG. 2C-7) are shown. The serial interface control and A/D logic  280  preferably includes a receiver  260  (FIG.  2 C- 1 ), a transmitter  262  (FIG.  2 C- 1 ), a serial-to-parallel converter  264  (FIG.  2 C- 2 ), an analog-to-digital converter (ADC)  266  (FIG.  2 C- 3 ), a monostable multivibrator  268  (FIG.  2 C- 6 ), an 8-bit parallel-to-serial shift register  270  (FIG.  2 C- 6 ), D-latches  272  (FIG. 2C-6) and  274  (FIG. 2C-9) and various other discrete components as shown. Although the circuit shown represents the preferred interface and A/D logic for each charger module  200 , any other circuit that performs the similar functions to that shown in FIG. 2C is acceptable as well. 
     Referring still to FIG. 2C, signals from the controller module  400  are received by receiver  260  which preferably is a DS26C32 manufactured by National Semiconductor. The data received is in a serial format and is converted to a parallel format by serial-to-parallel converter  264 . As shown, some of the data received from the controller module  400  represents status information such as whether leakage current has been detected (LEAKAGEBLU 0  and LEAKAGEBLU 1 ) and whether a temperature has been detected that is outside a specified preferred range (TEMPRED 0  and TEMPRED 1 ). Because each charger module  200  can charge two batteries, two sets of status information are transmitted from the controller module  400 —one set is related to one of the two batteries and the other information set is related to the other battery. Much of the status data decoded by the serial-to-parallel converter  264  is used to drive various status LED&#39;s  288  which preferably are mounted on a front panel (not shown) of the charger system  100 . 
     The controller module  400  is able to inhibit charging when desired. Disabling charging may be desirable when an overtemperature, overvoltage, or any other predefined condition is detected. The controller module  400  disables charging by providing an INHIBIT signal to the targeted charger module  200  to be disabled. As shown in the preferred embodiment of FIG. 2C, two individual INHIBIT signals, INHIBIT 0  and INHIBIT 1  are provided to turn on or off each PWM port separately. The INHIBIT signal is provided to the inhibit circuit of FIG. 2A, and when asserted disables the charger IC  220  from charging the associated battery. Through the INHIBIT signals, the controller module  400  provides the second level of intelligence discussed above. 
     Referring still to FIG. 2C, various charging parameters, such as battery current (CURRENT 0  and CURRENT 1 ) and voltage (VOLTAGE 0  and VOLTAGE 1 ), temperature (TEMP 0  and TEMP 1 ), and the leakage current (FLOAT 0  and FLOAT 1 ) are provided in analog form to the ADC  266 . The ADC  266  converts those signals to a digital representation which then is provided from the data out (DO) pin of ADC  266  to the serial input pin (SER) of parallel-to-serial shift register  270 . The shift register  270  generates preferably a single serial bit stream including all data and information desired to be transmitted to the controller module  400 . Other parameters or status information may be provided to shift register  270  for transmission to the controller module  400  in addition to the serial data provided by the ADC  266 . As shown, the QSEL and TSEL signal values are also provided to shift register  270 . The monostable multivibrator  268  preferably provides a control signal from its Q′ output pin (pin  4 ) to pin  1  of the shift register  270  to initiate and control the shifting of the data through the shift register. As the data is shifted through the shift register  270 , it is latched by D latches  272  and  274  for transmission through transmitter  262  to the controller module  400 . 
     Referring now to FIG. 3A, which is comprised of nine subfigures entitled FIGS. 3A-1 through  3 A- 9 , and FIG. 3B, which is comprised of six subfigures entitled FIGS. 3B-1 through  3 B- 6 , the controller module  400  generally includes a 24 VDC input circuit  402  (FIG.  3 A- 1 ), a microprocessor  410  (FIG.  3 A- 4 ), electrically erasable programmable read only memory (EEPROM)  416  (FIG.  3 A- 8 ), memory  420  (FIG.  3 A- 9 ), reset circuit  424  (FIG.  3 A- 2 ), real time clock  430  (FIG.  3 A- 9 ), serial interface port  440  (FIG.  3 A- 3 ), RS 422  line driver circuit  480  (FIG.  3 B- 1 ), and temperature sense circuit  490  (FIG.  3 B- 3 ). The circuit shown in FIGS. 3A and 3B represents an exemplary embodiment of one of a multitude of different controller circuits that could be used. A microprocessor is preferred, but the controller module  400  can be implemented without it. The controller module  400  shown preferably communicates with each of the charger modules  200 . The communication interface to each charger module  200  is shown best in FIG. 3B by way of RS 422  line driver circuit  480 . Generally, circuit  480  permits two-way communication with the charger modules  200  as will be described in detail below. The charger modules can transmit any desired charging status parameters, such as battery voltage and current, temperature, and error conditions, to the controller module  400 . The controller module  400 , via the RS 422  line driver module  480 , transmits charge control parameters to the charger modules  200 . 
     If desired, each charger module  200  can provide battery voltage and current values to the controller module  400 . These values are provided to the microprocessor  410  which can calculate and keep track of how much energy has been delivered to each battery. The microprocessor  410  preferably determines when a predetermined amount of energy has been delivered to the battery. That predetermined amount of energy may be representative of a level that corresponds to a fully charged battery. Thus, the controller module determines the end of charge condition based on energy provided to the battery. 
     It may also be desirable for the controller module  400  to keep track of the relative condition, age or health of a battery being charged. The battery condition, age and health can be estimated by analyzing the charging process of a battery being charged. The relative health and condition of a battery can be quantified and preferably stored in memory  420  and the controller module  400  can alert an operator that a battery needs to be replaced when its health and condition drop below a predetermined level. The alert can be provided through the serial interface  440 , described below. Alternatively, or additionally, the controller module  400  can disable charging to a particular battery once the battery&#39;s condition falls below the predetermined level by asserting the inhibit signal to the charger module  200  associated with that battery. 
     Referring to FIG. 3A, the microprocessor  410  preferably is a 68HC111F1 processor manufactured by Motorola, but alternatively may include any other suitable type of processor or microcontroller. The EEPROM device  416  preferably is 28C64A-10PLCC or other suitable memory device. The memory device  420  preferably is a static random access memory (RAM) device such as a KM62256BLP-10 or other suitable device. The EEPROM  416  preferably stores code to be executed by processor  410 . The static RAM device  420  preferably is used as temporary storage for configuration parameters and other types of data. The processor  410  can write data to and read data from static RAM  420 . 
     The reset circuit  424  generally comprises a reset device U 5  and associated resistors R 4  and R 5 , capacitors C 12  and C 13  and lithium battery BT 1 . The battery BT 1  permits the controller module  400  to retain settings in static RAM even if power is lost from the power supply module  110 . The reset device U 5  preferably is a MAX691 or other suitable device and generally maintains the processor  410  in a reset or inhibited state, by holding the RESET* signal low, until the power supply voltage to the processor has stabilized following an initial power up condition. Once the 24 VDC voltage prom power supply module  110  has stabilized, U 5  releases RESET* (RESET* goes high) and the processor  410  completes its initialization process. 
     The real time clock circuit  430  preferably includes a MC68HC68T1 clock device and associated resistor R 11 , capacitors C 17  and C 18 , diode D 1 , and crystal oscillators X 3  and X 4 . The real time clock circuit  430  provides time of day and date data to the processor  410 . The RTC INT signal is provided as an interrupt input signal to the processor  410  and is used to provide a wake up alarm signal that will notify the processor to update or execute time of day or date driven event tasks. 
     The charge controller module  400  also includes a serial interface  440  that preferably includes a MC145407 level converter U 4  coupled to capacitors C 8 , C 20 , C 21 , C 22 , C 23 , C 40 , resistors R 9  and R 10  and fuses FB 1  and FB 2  as shown in FIG. 3A. A computer or terminal can be connected to the serial interface  440  and used to download programming code and configuration data for controlling the charging protocol of a single battery or a set of batteries. Further, battery charge status information can be uploaded through the serial interface  440  if desired. Additionally, the serial interface  440  can include conventional circuitry to permit a wireless communication link with a remote terminal. For example, the serial interface  440  can include satellite transmission circuitry to permit a communications link with remote terminal via a satellite. 
     The communication between a terminal connected to the serial interface  440  and the charger controller  400  can include any suitable type of communication scheme. In accordance with the preferred embodiment, however, the communication scheme includes transmitting ASCII characters which encode various commands from the terminal to the serial interface  440  which then are interpreted and executed by the processor  410 . The ASCII character command set preferably includes the commands and the associated descriptions shown in Table II below. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Command Set. 
               
             
          
           
               
                   
                 Short 
                   
               
               
                 Command 
                 Command 
                 Description 
               
               
                   
               
               
                 AMP 
                 A 
                 Display energy in amp-hours stored into battery 
               
               
                   
                   
                 on this port up to this point in time. 
               
               
                 CHARGE 
                 G 
                 Start/restart charging progress on this port. 
               
               
                 HELP 
                 H 
                 Display the commands 
               
               
                 LOG 
                 L 
                 Displays current, voltage, amp-hours, &amp; temp 
               
               
                   
                   
                 continuously using *CSV on port 0 
               
               
                 PORT 
                 P 
                 Displays current, voltage, amp-hours, &amp; temp 
               
               
                   
                   
                 of port. 
               
               
                 STOP 
                 S 
                 Stops charging process for port. 
               
               
                 TEMP 
                 T 
                 Shows battery temperature in ° C. of port. 
               
               
                 VOLT 
                 V 
                 Shows battery voltage of port. 
               
               
                   
               
             
          
         
       
     
     Referring now to FIG. 3B, RS 422  line driver circuit  480  preferably includes a 1-of-8 decoder/demultiplexer U 10  (MM74HC138), four buffers U 11 A, U 11 B, U 12 A, U 12 B (MM74HC244), eight RS 422  transmitters U 13 -U 20  (DS26C31), two RS 422  receivers U 21  and U 22  (DS26C32) and eight-to-one multiplexer U 9  (74C151SC ND). Data flowing from the controller module  400  to the charge modules  200  is generated or otherwise provided by the processor  410  as the Master Out Slave In (MOSI) serial output signal (pin  31  of the processor  410 ). The MOSI output data may include status signals, configuration data or any other desired information. The MOSI output signal is provided via buffer U 12 B to the various RS 422  transmitters U 13 -U 20  as shown in FIG. 3B. A system clock (SCK) is also provided through buffer U 12 A to the various RS 422  transmitters. The charger controller  400  preferably communicates with one charge module  200  at a time. To initiate communications with a particular charge modules  200 , the processor  410  generates a three-bit binary value on pins  25 - 27  which are labeled PORTC:PORTA. A three-bit value can encode as many as eight different values and each value encoded by PORTC:PORTA corresponds to a particular charger module  200 . Thus, for example, if the processor  410  is to communicate with the second charger module  200 , the processor  410  generates a value of &#39;010&#39; (binary 2) for PORTC:PORTA. The processor  410  also generates a port enable signal PORTEN which enables communication in to and out of the charge controller  400 . The battery charger system  100  shown in FIG. 1 includes six charger modules  200 . Controller module  400  can communicate with as many as eight charger modules and even more with modifications easily made by one of ordinary skill in the art. 
     Referring still to FIG. 3B, the PORTC:PORTA value is provided to the input signals marked A, B, and C of the 1-of-8 decoder/demultiplexer U 10 . In response, U 10  asserts one of its eight output enable lines (Y 0 :Y 7 ) corresponding to the particular PORTC:PORTA value provided on the input lines. Thus, for a PORTC:PORTA value of binary 2, U 10  asserts the second output enable line (Y 2 ) high. Each enable line from U 10  is provided through one of the buffers U 11 A, U 11 B to an RS 422  transmitter U 13 -U 20 . Each charger module  200  only responds to signals from the charge controller  400  when the enable line associated with that particular charger module  200  is asserted; otherwise, the charger module  200  ignores signals from the controller module  400 . 
     As described, each charger module  200  receives a system clock signal, an enable signal and a data signal from the charge controller  400 . The system clock signal is used in accordance with conventional RS 422  protocol to synchronize transmission of information between transmitters and receivers. Each charger module  200  provides data to the charge controller  400  and is received by the RS 422  receivers U 21 , U 22 . The data from the receivers U 21 , U 22  then is multiplexed by multiplexer U 9  under control by the PORTC:PORTA and PORTEN signals. 
     The temperature sense circuit  490  preferably includes a processing circuit to process temperature signals from one or two temperature sensors (not shown) coupled to connector J 5 . The temperature sensors may be thermocouples or other suitable temperature sensitive devices and can be located anywhere such as fixedly attached to the enclosure (not shown) that houses the charger&#39;s electronics. Each circuit preferably includes an operational amplifier (LM6134A) particularly suited for processing temperatures signals. The output signals from the temperature sense circuits is labeled as TEMPA and TEMPB and preferably are provided directly to pins  59  and  61  of processor  410 . The processor  410  can be programmed to take appropriate action in the event the temperature becomes too high or too low. The action could be any suitable action such as stopping the charging of the batteries. 
     The above discussion is meant to be illustrative of the principles of the present invention. However, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.