Abstract:
A system for determining the operating characteristics of an energy source. The system comprises a controller for generating and shaping a time-varying voltage signal for application to the energy source; a converter for receiving from the energy source a time-varying return voltage signal and for converting the tire-varying return voltage signal into a digital signal. The amplitude of the time-varying return signal contains information representative of the operating characteristics of the energy source. The time-varying return voltage signal is produced in response to the time-varying voltage signal. The controller is responsive to the digital signal and determines the operating characteristics of the energy source. The controller generates display signals, and the display signals are representative of the operating characteristics of the energy source. The system also includes a display for displaying the display signals.

Description:
FIELD OF INVENTION 
     This invention relates generally to systems for testing the conditions of lead-acid batteries, as well as starters and alternators used in conjunction with the batteries. In particular, the present invention relates to such testers that are microprocessor-controlled hand-held units. 
     BACKGROUND 
     The following symbols will have the following meanings in the description of the preferred battery testing system embodying this invention: 
     V(bat) The terminal voltage of the battery. 
     V(d) Voltage drop across the battery due to an internal resistance and a load current. 
     CA Cranking Amps, the current that the battery can supply for 30 seconds at full charge and at 70° F. and not drop the battery voltage below 1.2 volts per cell. 
     Cold Cranking Amps (CCA) are defined by the Battery Council International (BCI) as “the number of amperes a battery at 0° F. (−17.8° C.) can deliver for 30 seconds and maintain, at least, a voltage of 1.2 volts per cell (lead-acid)”. For example, a 12-volt lead-acid battery having 6 cells with 1.2 volts/cell must not drop below 7.2 volts. A fully charged battery has an open circuit voltage of 12.6 volts. The voltage drop from 12.6 volts to 7.2 volts is 5.4 volts. Therefore, at 0° F., the CCA of the battery is the current that the battery can supply and drop the voltage not more that 5.4 volts at the end of 30 seconds. For a 6-volt lead-acid battery, the maximum drop is 2.7 volts and for a 24-volt lead-acid battery, the maximum drop is 10.8 volts. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved hand-held testing unit that uses a microprocessor to perform test measurements on lead-acid batteries and the systems in which they are used, including the starters and alternators in such systems. 
     A specific object of one preferred embodiment of the invention is to provide such a hand-held testing system which is light and portable and yet is capable of subjecting lead-acid batteries to a load test drawing current as high as 200 amperes from the battery. 
     Still another object of the invention is to provide a hand-held battery testing system that is capable of subjecting a lead-acid battery to a load test without significantly reducing the state-of-charge of the battery. 
     Another object of the invention is to provide such a hand-held testing system that permits the user to load test a lead-acid battery, check the condition of the alternator, and perform a starter draw test with ease, using a single test unit. 
     Still another object of the invention is to provide such a testing unit that permits the test results to be printed and/or downloaded to a computer. 
     Yet another object of the invention is to provide a hand-held testing system that can also be used as a voltmeter. 
     In this connection, a related object of the invention is to provide such a system that automatically checks whether the tester is properly connected to the battery before the battery is subjected to the load test. 
     In accordance with the present invention, the foregoing objectives are realized by providing a system that determines the condition of a lead-acid battery by measuring the beginning voltage across the terminals of the battery in the absence of a load; connecting the battery to a first load, measuring the AC ripple in the output current drawn from the battery by the first load, and computing an estimated CCA of the battery using the beginning voltage and the AC ripple; connecting the battery to a second load that draws more current from the battery than the first load and measuring the loaded voltage of the battery, and evaluating the condition of the battery at least in part on the basis of the beginning voltage and the estimated CCA. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a hand-held battery and charging system analyzer embodying the invention; 
     FIG. 2 is a block diagram of the testing system in the analyzer shown in FIG. 1; 
     FIG. 3 is a circuit diagram of a portion of the system illustrated in FIG. 2, including the microprocessor and its display, keypad and nonvolatile memory; 
     FIG. 4 is a circuit diagram of a power supply circuit used in the system illustrated in FIG. 2; 
     FIGS. 5 a  and  5   b  are circuit diagrams of two load circuits used in the system illustrated in FIG. 2; 
     FIG. 6 is a circuit diagram of an analog conditioning and AC amplifier/rectifier circuit used in the system illustrated in FIG. 2; 
     FIG. 7 is a flow chart of the main software program executed by the microprocessor in the battery tester system of FIG. 2 to initiate operation of the system; 
     FIG. 8 a  is a flow chart of the “check battery” subroutine accessed by the program of FIG. 7, and 
     FIG. 8 b  is a flow chart of a “measure CCA” subroutine accessed by the subroutine of FIG. 8 a ; 
     FIG. 9 is a flow chart of the “check alternator” subroutine accessed by the program of FIG. 7; 
     FIG. 10 is a flow chart of the “battery test” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 11 is a flow chart of the “alternator test” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 12 is a flow chart of the “starter test” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 13 is a flow chart of the “voltmeter” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 14 is a flow chart of the “review/print” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 15 is a flow chart of the “communicate with PC” subroutine that is accessible by manual selection from a menu generated by the program of FIG. 7; 
     FIG. 16 is a sectional view taken transversely through the lower half of the testing unit shown in FIG. 1; 
     FIG. 17 is a bottom plan view of the printed circuit board included in the sectional view of FIG. 16; 
     FIG. 18 is a sectional view taken transversely through the upper half of the testing unit shown in FIG. 1; 
     FIG. 19 is a perspective front view of the internal structure of the testing unit shown in FIG. 1, showing the top surface of the printed circuit board and only one side wall of the housing; and 
     FIG. 20 is a perspective front view of the analyzer shown in FIG. 1 without the keys, taken from the lower end of the unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An illustrative embodiment of a hand-held tester is described below as it might be implemented to provide for improved methods of determining the operating conditions of lead-acid batteries, and starters and alternators used with such batteries. 
     FIG. 1 is a perspective view of the front and bottom of a hand-held tester embodying the invention. The front panel  10  includes an on/off switch  11 , a print switch  12  and four manual keys  13 ,  14 ,  15  and  16  that are used in conjunction with a liquid crystal display (LCD)  17 . The keys  13 - 16  provide input signals to a microprocessor that controls the operation of the tester, including the messages or data displayed on the LCD  17 . A pair of battery cables  18   a  and  18   b  extend from one end of the hand-held unit for connection to the posts of a lead-acid battery B to be tested. A reverse-connection indicator  19  on the front panel  10  is illuminated when the cables are connected to the wrong posts of the battery. The reverse connection indicator  19  is simply an LED having its anode connected to the small wire of the negative battery cable and its cathode connected through a current-limiting resistor to the positive battery cable. 
     The overall tester system is illustrated by the block diagram in FIG.  2 . The system is controlled by a microprocessor  20  that receives power from a power supply  21  which in turn is powered by the lead-acid battery B under test. A 9-volt battery  22  provides an alternative power source when the tester is not connected to a battery B to be tested. The microprocessor  20  receives input signals from the four manually operated keys  13 - 16 , an analog conditioning circuit  23 , and an AC amplifier/rectifier circuit  24 , as will be described in more detail below. The microprocessor  20  provides output signals to the LCD  17  for communicating with the user, to an infrared printer port  25  for printing results for the user, to a serial port  26  for communicating with an off-board computer such as a PC  26   a , to a pair of load circuits  27  and  28  that can be connected to the battery B for load testing, and to an audio buzzer  30  for providing audible alarms or signals to the user. The microprocessor  20  is also connected to a nonvolatile memory  29  for storing and retrieving data that is to be preserved in the event of a loss of power to the system. 
     FIG. 3 is a more detailed diagram of the system illustrated in FIG.  2 . The microprocessor  20 , which has a built-in analog-to-digital converter, receives 
     an ON/OFF input signal from the power supply circuit  21  shown in more detail in FIG. 4, 
     an ON_SW signal from the on/off key  11   
     KEY 1 , KEY 2 , KEY 3 , KEY 4  and KEY 5  signals from the four manually operated keys  13 - 16  and the print key  12  via a pull-up resistor network  31 , 
     a BAT_VOLTS signal from the analog conditioning circuit  23  shown in more detail in FIG. 6, 
     an AC_VOLTS signal from the AC amplifier/rectifier circuit  24  shown in more detail in FIG. 6, 
     oscillator signals from an oscillator comprising a crystal  30 , a pair of capacitors C 1  and C 2 , and a current-limiting resistor R 1 , and 
     data signals from the non-volatile memory  29 . 
     Output signals produced by the microprocessor  20  are: 
     display-generating signals to the 4×16 LCD  17  which also receives Vcc at terminal  2  and a reduced Vcc at terminal  3  to set the LCD contrast (the reduction is achieved by a voltage divider formed by a pair of resistors R 2  and R 3  connected between Vcc and ground, with terminal  3  of the LCD receiving the voltage that exists between the two resistors), 
     a POWER signal for the power supply circuit  21  shown in FIG. 4, 
     a PRINTER signal for the infrared transducer used to communicate with printers, 
     switching signals LOAD 1 , LOAD 2 , LOAD 3  and CCA_LOAD supplied via pull-down resistors  32  and current limiting resistors  33  to control FETs that connect and disconnect various loads to the battery being tested, and data signals to be stored in the non-volatile memory. 
     Coupling to a printer is effected by an infrared coupling diode  99  mounted in the upper end of the tester (see FIGS.  1  and  3 ). The PRINTER signal from the microprocessor  20  is supplied via resistor R 4  to the base of a transistor T 1 . When the transistor T 1  is turned on, current flows from a Vcc source through the diode  99 , a resistor R 5  and the transistor T 1  to ground. The power supply  21  is illustrated in more detail in FIG.  4 . The BUS+ input to the power supply circuit is connected to the large wire of the positive battery cable, and ground is connected to the large wire of the negative battery cable. The supply current from the BUS+ input passes through a blocking diode D 10  and a resettable fuse F 1  that trips under high currents, then resets after allowing for a period to reset. The diode D 10  prevents damage to the tester if the leads connected to the battery are reverse-connected. When the battery cables are not connected to a battery, the power supply circuit is powered by the 9-volt battery  22  through a blocking diode D 11 . 
     The power supply circuit is turned on by the ON_SW signal from the on/off switch  11 , and then is kept on by the POWER output signal from the microprocessor  20 . These signals turn on either switching transistor T 10  or switching transistor T 11  to draw current through a pull-up resistor R 10 . Specifically, the signal ON_SW is applied to the base of the switching transistor T 10  through a current-limiting resistor R 11  and is also supplied to a pull-down resistor R 12  connected to ground. An ON/OFF signal to the microprocessor  20  is also supplied from the keypad through a second current-limiting resistor R 13 , and a voltage-limiting zener diode D 12  which is connected from the ON/OFF terminal to ground. The POWER signal from the microprocessor  20  is supplied to the base of the switching transistor T 11  through a current-limiting resistor R 14 . 
     A low voltage at the collector of either transistor T 10  or T 11  turns on a field effect transistor (“FET”)  10 , which then supplies current from the BUS+ input to the input terminal of a voltage-regulating IC  100  to switch on the power. The gate of the FET  10  is protected by a resistor R 15 , and a pair of filter capacitors C 10  and C 11  are connected in parallel from the input of IC  100  to ground. The output of the IC  100  is connected to a terminal Vcc which is connected to a conventional voltage converter to furnish −5 volt power throughout the unit. Three filter capacitors C 12 , C 13  and C 14  are connected in parallel from the terminal Vcc to ground. A voltage divider is formed by a pair of resistors R 16  and R 17  to supply a desired voltage level to the “adjust” input of the IC  100 . The voltage level Vin that exists between the resistor R 10  and the fuse F 1  is supplied to the keypad, as shown in FIG.  4 . 
     The power supply circuit can be turned off by the microprocessor  20  sending a low signal to the POWER output after the on/off switch  11  has been pressed or after the unit has been on for two minutes with no activity. When the on/off switch  11  is pressed while the power supply is on, the resulting change in the ON_SW signal is sensed by the microprocessor  20 , which responds by producing a low POWER signal. This turns off the transistor T 11 , which turns off the power supply. 
     The two load circuits  27  and  28  are shown in more detail in FIGS. 5 a  and  5   b , respectively. The low-current load circuit of FIG. 5 a  is connected to the battery to receive the BUS+ input by a CCA_LOAD signal from the microprocessor  20 . The CCA_LOAD signal turns on a switching FET  20  so that current can flow from the BUS+ input through a reverse-blocking diode D 20  and a current-setting resistor R 20  to ground. As will be described in more detail below, the low-current load is connected to the battery when it is desired to determine an estimated CCA for the battery under test. 
     The high-current (e.g., 200-amp) load bank circuit of FIG. 5 b  comprises three parallel resistors R 21 , R 22  and R 23 , each of which can be connected to the battery by its own separate signal LOAD 1 , LOAD 2  or LOAD 3  which turns on a corresponding switching FET  21 ,  22  or  23  so that current can flow from the battery (BUS+) through reverse blocking diodes D 21 -D 26  and one or more of the resistors R 21 -R 23  to ground. As will be described in more detail below, the 200-amp load is connected to the battery when it is desired to load test the battery to evaluate its condition. 
     The analog conditioning circuit  23  and the AC amplifier/rectifier circuit  24  are shown in FIG.  6 . The analog conditioning circuit  23  is connected to the terminals or posts of the battery B for measuring the voltage across those posts. The connections to the battery terminals are made with the clamps on the ends of the battery cables  18   a ,  18   b  extending from the lower end of the test unit. These clamps are preferably kelvin style battery clamps  35   a  and  35   b  whose twin positive and twin negative leads (and contacts) are insulated from each other. The VOLTS+ input to the circuit  23  is connected to the small wire of the positive battery cable, while the VOLTS− input is connected to the small wire of the negative battery cable. A pull-down resistor R 40  is connected between the two cables  18   a  and  18   b.    
     In FIG. 6, the VOLTS+ and VOLTS− inputs are connected to the + and − inputs of an operational amplifier  40  via gain-setting resistors R 41 -R 44  in a difference amplifier configuration. The output of the operational amplifier  40  furnishes the analog BAT_VOLTS signal that represents the output voltage of the battery being tested. This signal is one of the inputs to the microprocessor  20  and its internal analog-to digital (A/D) converter. 
     The output of the operational amplifier  40  is also supplied through an AC coupling capacitor C 40  to the AC amplifier/rectifier circuit  24  to produce a DC output representing the magnitude of any AC ripple in the battery voltage. Specifically, the capacitor C 40  is connected through a gain-setting resistor R 45  to the negative input of an operational amplifier  41  whose positive input is connected to a pull-down resistor R 46 . The output of the amplifier  41  is connected to a pair of rectifying diodes D 40  and D 41 , and an integrating capacitor C 41  is connected in parallel with the two diodes. The resulting DC output of the circuit  24  furnishes the AC_VOLTS signal that represents the magnitude of the AC ripple and is one of the inputs to the microprocessor  20 . 
     Turning now to the main program that is shown in FIG.  7  and executed by the microprocessor  20 , this program is entered when the microprocessor detects that the power supply is turned on. The first step  100  of the main program displays an introductory message on the LCD  17 , informing the user that the unit is “ready to connect” to a battery to be tested. At this point the user may press the enter key  15 , detected at step  101 , to cause the program to jump ahead to step  102  where a menu is displayed to provide the user with multiple options. The options are battery test, starter test, alternator test, review/print, volt meter and download/setup. 
     Whenever the menu is displayed at step  102 , the system waits for the user to select one of the options by pressing the up or down key  13  or  14  to scroll to the desired option and then pressing the enter key  15 . Each selection calls one of six subroutines at one of the six steps  110 - 115 . If no option is selected within a time-out interval measured by the microprocessor  20 , or if the on/off key  11  is pressed, the subroutine is exited at step  116 . The subroutine may also be exited by pressing the escape key  16  at any time during display of the introduction at step  100  or the options menu at step  102 . Pressing of the escape key  16  is detected at step  117 . 
     If the user does not press the enter key  15  when the introductory message is displayed at step  100 , the system waits for the user to connect the tester to a battery, which is detected at step  103 . The program then advances to step  104  where a message is displayed to prompt the user to “enter approximate battery temperature” in degrees F. The user enters the temperature by using up/down keys  13 ,  14  to scroll through the displayed battery temperatures and select the appropriate temperatures, and then pressing the enter key  15  to enter the selected temperature. The selected temperature is stored in the internal RAM of the microprocessor  20 . 
     After the selected battery temperature has been entered, the system advances to step  105  which detects whether the engine-driven alternator connected to the battery B is running, by measuring the AC ripple represented by the AC_VOLTS signal from the amplifier/rectifier circuit  24 . An AC ripple greater than 4 mV means that the engine is running. An affirmative response at step  105  advances the system to step  106  which calls a “check alternator” subroutine. A negative response at step  105 , i.e., detection of an AC ripple that is less than 4 mV, causes the system to proceed to step  107  to call a “check battery” subroutine. When either subroutine is completed, the options menu is displayed at step  102 . 
     The “check battery” subroutine, which is illustrated by the flow charts in FIGS. 8 a  and  8   b  and is entered at step  200  in FIG. 8 a . The first step  201  of this subroutine reads and stores the BAT_VOLTS signal from the circuit  23 . At this point there is no load connected to the battery, so the BAT_VOLTS signal represents the open-circuit voltage across the battery terminals. The system then advances to step  202  which determines whether the battery B being tested is a 24-volt battery by determining whether the voltage read at step  201  is above 17 volts. An affirmative answer means the battery is a 24-volt battery, and the system proceeds directly to step  203  to determine the state of charge of the battery (described below). A negative answer at step  202  means the battery is not a 24-volt battery, and the system advances to step  204  which calls the subroutine of FIG. 8 b  to compute the CCA of the battery. 
     The subroutine of FIG. 8 b  is entered at step  250  and begins pulsing the low-current load circuit  27  at step  251 . Specifically, the FET  20  in the low-current load circuit  27  is turned on and off at a frequency of 100 cycles/second for two seconds for 12-volt batteries, or at a frequency of 50 cycles per second for two seconds for 6-volt batteries (whether the battery is a 6-volt or 12-volt battery is determined by whether the BAT_VOLTS signal is above or below 7.5 volts). After the two seconds of pulsing, the magnitude of the AC ripple is measured at step  252 , in the same manner described above, and then the estimated CCA is computed at step  253  using the formula: 
     
       
         CCA est =[CCA Coef+Temperature Coef.×(70−Temperature)+Volt Coef.×(12.68−Voltage)]/AC Ripple 
       
     
     The values of the three coefficients CCA Coef, Temperature Coef and Volt Coef in the above formula are determined empirically and stored in the program memory of the microprocessor. Typical values are as follows: 
     12-volt battery 
     CCA Coef=6750 
     Temperature Coef=3200 
     Volt Coef=16 
     6-volt Battery 
     CCA Coef=1900 
     Temperature Coef=970 
     Volt Coef-=4.8 
     The resulting CCA value is stored, and then the subroutine ends at step  254  and proceeds to step  203  where the state of charge of the battery is interpolated from the battery&#39;s beginning terminal voltage according to the following table from Battery Council International (BCI): 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Charge 
                 12-volt battery voltage 
               
               
                   
                   
               
             
             
               
                   
                 100%  
                 12.65 
               
               
                   
                 75% 
                 12.45 
               
               
                   
                 50% 
                 12.24 
               
               
                   
                 25% 
                 12.06 
               
               
                   
                  0% 
                 11.89 
               
               
                   
                   
               
             
          
         
       
     
     The condition of the battery B is then evaluated using the following logic (for a 12-volt battery): 
     If the CCA is less than 40 amps, report BAD BATTERY 
     Otherwise, if the voltage is above 12.25 volts, report CONTINUE TESTING 
     Otherwise, if the voltage is above 10.80 volts, report CHARGE &amp; TEST 
     Otherwise, if the voltage is below 9.80 volts, report CHARGE &amp; TEST 
     Otherwise, if the voltage is between 9.80 and 10.80 volts, report BAD CELL 
     In any of the above examples for a 12-volt battery, the voltages can be divided by two for 6-volt batteries and multiplied by two for 24-volt batteries. 
     The appropriate report from the above logic is logged in the nonvolatile memory at step  205 , and then displayed on the LCD at step  206 . After the results of the battery check have been displayed at step  206 , the system displays the options menu again at step  208  if the escape key  16  is pressed (as detected at step  207 ), prints the displayed results at step  210  if the print key  12  is pressed (as detected at step  209 ), or turns off at step  211  if the off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “check alternator” option is selected when the options menu is displayed at step  105  of the main program, the subroutine of FIG. 9 is called and is entered at step  300 . The first step  301  of this subroutine reads and stores the BAT_VOLTS signal, and then reads and stores the AC_VOLTS signal at step  302 . The system then advances to step  303  which logs the read values of the two signals along with an evaluation based on those values. Specifically, if the regulation voltage is less than 13.0 volts, the evaluation is “LOW REGULATION,” and if the voltage is greater than 15.0 volts, the evaluation is “HIGH REGULATION.” Otherwise the evaluation is “GOOD REGULATION.” If the AC ripple is greater than 50 mv, an additional evaluation of “BAD DIODE” is logged. The logged values and evaluations are all stored in the non-volatile memory  29 , and are displayed on the LCD  17  at step  304 . 
     After the results of the alternator check have been displayed at step  304 , the operation is identical to that described above for the “check battery” subroutine, i.e., the system displays the menu again at step  306  if the escape key  16  is pressed (as detected at step  305 ), prints the displayed results at step  308  if the print key  12  is pressed (as detected at step  307 ), or turns off at step  309  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “battery test” option is selected when the menu is displayed at step  102  of the main program, the subroutine of FIG. 10 is called and is entered at step  400 . The first step  401  of this subroutine displays a message that prompts the user to set the rated CCA of the battery B by adjusting the displayed value with the up and down keys  13  and  14  and then pressing the enter key  15 . Step  402  then checks the microprocessor memory to determine whether the battery temperature has been previously entered. If not, the user is prompted at step  403  to enter the approximate battery temperature, as described previously. After entry of the battery temperature, or if step  402  determines that the temperature has been previously entered, the system advances to step  404  where the BAT_VOLTS signal is read and stored. At this point there is no load connected to the battery, so the BAT_VOLTS signal represents the open-circuit voltage across the battery terminals. 
     At step  405 , the microprocessor computes the estimated CCA of the battery by calling the subroutine of FIG. 8 b.    
     Then at step  406  the open circuit voltage is used to determine whether the battery has a surface charge by determining whether the voltage read at step  404  is greater than 12.8 volts. If it does, the surface charge is removed at step  407  by cycling the loads in the 200-amp load bank  28  so that one load at a time is connected to the battery for a 2.5-second interval, followed by a 3-second delay, followed by connection of another load to the battery. Specifically, each of the three resistors R 21 -R 23  is connected to the battery for about 0.1 second each (drawing about 70 amps) in sequence, and this cycle is repeated throughout the 2.5-second interval. At the end of the 2.5-second interval, no load is connected to the battery during the 3-second delay, and then the magnitude of the BAT_VOLTS signal is checked at the end of the delay interval to determine whether the battery voltage has dropped below 12.75 volts. This process is repeated, up to a maximum of three times, until a BAT_VOLTS value of less than 12.75 volts is measured at the end of one of the 3-second delay intervals. 
     After the surface charge has been removed at step  407 , or if the battery was determined to have no surface charge at step  406 , the system determines whether the battery is over 50% charged at step  408 . If the answer is affirmative, the battery is load tested at step  409 , and then the results are evaluated and logged at step  410  and displayed at step  411 . For the load test at step  409 , all three load resistors in the 200-amp load bank  28  are connected to the battery for 1.5 seconds if the beginning battery voltage (read at step  404 ) is greater than 12.44 volts, or for one second if the beginning battery voltage is greater than 12.25 volts but less than 12.44 volts. The pass voltage for the load test is based on the rated CCA entered at step  401 , as follows 
     
       
         Pass voltage=(Rated CCA×0.002)+8.85. 
       
     
     If the answer at step  408  is negative, meaning the battery is less than 50% charged, the results are evaluated and logged at step  410  and displayed at step  411  without carrying out the load test. 
     The evaluation of the results at step  410  is carried out according to the following logic: 
     
       
         
               
             
           
               
                   
               
             
             
               
                 If the beginning voltage was above 12.25: 
               
               
                   If the loaded voltage was above the pass voltage: 
               
               
                   If the beginning voltage was above 13.0: 
               
               
                   Compare the estimated CCA to the rated CCA: 
               
               
                   If the estimated CCA is above 87% the battery is GOOD. 
               
               
                   If the estimated CCA is between 75% and 87% the battery is 
               
               
                   MARGINAL. 
               
               
                   If the estimated CCA is below 75% the battery is BAD. 
               
               
                   If the beginning voltage was between 12.25 and 13.0: 
               
               
                   Compare the estimated CCA to the rated CCA: 
               
               
                   If the estimated CCA is above 80% the battery is GOOD. 
               
               
                   If the estimated CCA is between 70% and 80% the battery is 
               
               
                   MARGINAL. 
               
               
                   If the estimated CCA is below 70% the battery is BAD. 
               
               
                   If the loaded voltage was below the pass voltage: 
               
               
                   The battery is BAD. 
               
               
                   If the beginning voltage was between 10.80 and 12.25: 
               
               
                   Compare the estimated CCA to the rated CCA: 
               
               
                   If the estimated CCA is between 80% and 20% the battery must 
               
               
                   be charged and retested. 
               
               
                   If the estimated CCA is less than 20% the battery is BAD. 
               
               
                   If the beginning voltage was between 9.80 ad 10.80: 
               
               
                   The battery has a BAD CELL. 
               
               
                   If the beginning voltage was below 9.80: 
               
               
                   The battery is BAD. 
               
               
                   
               
             
          
         
       
     
     After the results of the battery evaluation have been displayed at step  411 , the operation is identical to that described above for the “check battery” subroutine, i.e., the system displays the menu again at step  413  if the escape key  16  is pressed (as detected at step  412 ), prints the displayed results at step  415  if the print key  12  is pressed (as detected at step  414 ), or turns off at step  416  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “alternator test” option is selected from the options menu displayed at step  102  of the main program in FIG. 7, the subroutine of FIG. 11 is called and is entered at step  500 . The first step  501  of this subroutine determines whether the engine is running in the same manner described above for step  105  of the main program in FIG.  7 . If the answer is negative, the user is prompted to start the engine by a “start engine” message displayed on the LCD  17  at step  502 . After the engine has been started, or if it already running as determined by an affirmative response at step  501 , the BAT_VOLTS signal is allowed to stabilize at step  503 . Specifically, the value of BAT_VOLTS is displayed along with a message advising the user to “allow voltage to stabilize” and then press the “yes” key to continue. 
     After the voltage has stabilized, both the BAT_VOLTS signal and the AC_VOLTS signal are read at step  504  and used at step  505  to determine whether the alternator is a 24-volt alternator by determining whether the value of BAT_VOLTS is above 17 volts. If the answer is affirmative, the user is prompted at step  506  to turn on the accessory loads such as the headlights, air conditioner or heater, radio, etc. The value of the BAT_VOLTS signal is then read at step  507 , and the test results are evaluated and logged at step  508 . 
     If it is determined at step  505  that the alternator is not a 24-volt alternator, then the high-current load  28  is cycled on and off at step  509 . Specifically, one of the switching transistors FET 2 , FET 3  or FET 4  in the high-current load circuit is turned on if the BAT_VOLTS signal is greater than 12.8 volts, and is turned off if the BAT_VOLTS signal drops below 12.8 volts. This cycling is continued for 5 seconds while keeping track of the number of times the load is turned on. At the end of the 5-second load-cycling interval, the estimated alternator output current is computed at step  510 . If the load was on during the entire 5 seconds, then the alternator output current is estimated to be greater than 60 amps. If the load was on during only a portion of the 5 seconds, then the alternator output current is estimated to be: 
     
       
         40×(% time load was on)+20 
       
     
     The 20 in the above formula accounts for the “key draw” of current in an automotive electrical system. The test results are evaluated and logged at step  508  and displayed at step  511 . Specifically, the regulation voltage (BAT_VOLTS signal), AC ripple (AC_VOLTS signal) and the estimated alternator output current are logged and displayed along with an evaluation of whether the regulation is “low”, “high” or “good” according to the following logic: 
     If the regulation voltage is below 13.0 volts, then the regulation is “low.” 
     If the regulation voltage is above 15.0 volts, then the regulation is “high.” 
     If the regulation voltage is between 13.0 and 15.0 volts, then the regulation is “good.” 
     The logged and displayed results also include a “bad diode” indication if the AC ripple was greater than 50 mv. The “bad diode” indication means that the alternator should be replaced because the stator diodes are bad, which can cause a slight drain on the alternator output as well as causing other diodes to fail, eventually resulting in a failed alternator or dead battery. A “high” regulation can damage the system and thus indicates that the alternator should be repaired or replaced. 
     After the results of the alternator test have been displayed at step  511 , the operation is identical to that described above for the “check battery” subroutine, i.e., the system displays the menu again at step  513  if the escape key  16  is pressed (as detected at step  512 ), prints the displayed results at step  515  if the print key  12  is pressed (as detected at step  514 ), or turns off at step  516  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “starter test” option is selected from the options menu displayed at step  102  of the main program in FIG. 7, the subroutine of FIG. 12 is called and is entered at step  600 . The first step  601  of this subroutine determines whether the system is a 24-volt system in the same manner described above for step  505  of the “alternator test” subroutine in FIG.  11 . If the answer is affirmative, the value of the BAT_VOLTS signal is read at step  602  to determine the beginning voltage of the battery. Then the user is prompted to start the engine by a message displayed at step  603 , and the minimum value of the BAT_VOLTS signal is read at step  604  while the engine is being started. The beginning and minimum voltages are logged at step  605  and then displayed at step  606 . 
     If step  601  determines that the alternator is not a 24-volt alternator, then step  607  turns on all three FETs in the high-current load circuit  28  for one second, records the voltage drop, and uses the recorded voltage and known current (i.e. 200 amps) to compute the internal resistance of the battery. After the battery has been load tested at step  607 , the same operations described above for steps  602 - 604  are carried out at steps  608 ,  609  and  610 , respectively. The estimated starter current draw is then computed at step  611  using the following formula: 
     
       
         (Beginning voltage−Minimum voltage)/Resistance 
       
     
     The results are logged at step  605  and displayed at step  606 . Once again, after the results of the “starter test” have been displayed at step  606 , the operation is identical to that described above for the “check battery” subroutine, i.e., the system displays the menu again at step  613  if the escape key  16  is pressed (as detected at step  612 ), prints the displayed results at step  615  if the print key  12  is pressed (as detected at step  614 ), or turns off at step  616  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “volt meter” option is selected from the options menu displayed at step  102  of the main program in FIG. 7, the subroutine of FIG. 13 is called and is entered at step  700 . The first step  701  of this subroutine reads the value of the BAT_VOLTS signal and the AC_VOLTS signal and displays the results. Then if the escape key  16  is pressed, this event is detected at step  702  and the main menu is displayed at step  703 . If the escape key is not pressed, the system turns off at step  704  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     If the “review/print” option is selected from the menu displayed by the main program in FIG. 7, the subroutine of FIG. 14 is called and is entered at step  800 . The first step  801  of this subroutine reads and displays the logged results of the last test. The up and down keys  13  and  14  can then be pressed by the user to increment or decrement to the desired test. Then again the operation is identical to that described above for the “check battery” subroutine, i.e., the system displays the main menu again at step  803  if the escape key  16  is pressed (as detected at step  802 ), prints the displayed results at step  805  if the print key  12  is pressed (as detected at step  804 ), or turns off at step  806  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. Coupling to a printer is effected by an infrared coupler  99  mounted in the upper end of the tester (see FIGS.  1  and  3 ). 
     If the “download/setup” option is selected from the options menu displayed at step  102  of the main program in FIG. 7, the subroutine of FIG. 15 is called and is entered at step  900 . The first step  901  of this subroutine displays a message prompting the user to connect the unit to a PC if the unit is not already so connected. Connection to a PC is effected by inserting a stereo plug on an adapter cord into a jack  98  in the upper end of the tester, and plugging a serial adapter on the other end of the cord into a serial port in the PC. When the unit is connected to a PC, the test results stored in the hand-held tester can be downloaded to the PC at step  903  using a program in the PC such as “Windows 98 Hyper Terminal.” The user may also enter a name and address at step  902  which is stored in the nonvolatile memory  29  and printed at the top of a printout when the user prints the results to the portable infrared printer via the infrared communication port  99 . 
     If at any time the exit key of the PC or the escape key  16  of the test unit is pressed, that event is detected at step  904  or  905 , and the main menu is displayed at step  906 . The test unit turns off at step  907  if the on/off key  11  is pressed or after a two-minute timeout period if the user does nothing. 
     Structurally, the tester of FIG. 1 includes a strong, durable housing formed by a pair of extruded aluminum side members  80  and  81  joined at opposite ends by a pair of end plates  82  and  83  attached to the side members  80 ,  81  by multiple screws  84  (see FIGS.  1  and  20 ). The interior surfaces of the two side members  82 ,  83  form elongated slots  85  and  86  (FIG. 16) for receiving and supporting a printed circuit board  87  that carries all the electronic circuitry except for the three large resistors R 21 -R 23  that form the high-current load for the battery under test. Because of the high current levels, these resistors R 21 -R 23  dissipate a substantial amount of heat, and thus they are mounted in a ventilated end portion of the housing away from the printed circuit board  87 . The ends of the three resistors R 21 -R 23  are connected to a pair of insulating mounting plates  88  and  89  that fit into mating slots  88   a,    88   b  and  89   a ,  89   b  formed in the interior surfaces of the respective side members  80 ,  81  (see FIG.  18 ). A third plate  90  extends across the upper end of the printed circuit board  87  and overlaps the lower ends of the plates  88  and  90 . The mounting plates  88 ,  89  and the third plate  90  combine to form an effective heat shield from the heat dissipated in the resistors R 21 -R 23  during high-current load testing of a battery. 
     The bottom U-shaped panel  10  (FIGS. 1 and 20) fits into two pairs of elongated slots  91 ,  92  and  95 ,  96  (see FIG. 18) formed in the interior surfaces of the two side members  80  and  81 . The panel  10  extends from the lower ends of the side members  80 ,  81  to at least the upper end of the printed circuit board  87 . Similarly, a vented U-shaped top panel  82  fits into the other ends of the two pairs of elongated slots  91 ,  92  and  95 ,  96  formed in the interior surfaces of the side members  80  and  81  and extends to meet the bottom panel  10 . The entire top panel  82 , including the two extensions  82   a  and  82   b , is apertured (see FIGS. 1 and 20) to facilitate the dissipation of heat from the three resistors R 21 -R 23 . 
     As can be seen in FIGS. 17 and 19, the printed circuit board  87  carries two rows of TO- 220  packaged devices, including the switching transistors FET 1 O, FET 20 , FET 21 - 23  and the voltage regulator  100  and the diodes D 21 -D 26 , mounted along opposite edges of the board  87 . These TO- 220  packaged devices are mounted on a pair of aluminum strips  87   a  and  87   b  that overlap the edge portions of the printed circuit board  87  and extend into mating slots in the side members  80  and  81  (see FIG. 19) to assist in dissipating heat from the components, especially when the 200-amp load is being utilized. 
     The two cables  18   a  and  18   b  that connect the test circuitry to the battery B are connected to copper plates  96  and  97  near the lower end of the printed circuit board  87 , as can be seen in FIG.  17 . These copper plates  96  and  97  mount to the back of the printed circuit board  87  and carry the high current that flows through the diodes D 21 - 26 , the loads R 21 - 23  and the transistors FET 21 - 23  to the cables  18   a  and  18   b . These copper plates permit the use of small components such as the TO- 220  packaged devices, despite the high current levels. 
     While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention, which is set forth in the following claims.