Abstract:
A systematic method and system for testing the charging and starting systems of a vehicle, which requires each individual test to pass before proceeding is provided. In addition, the system and method incorporates an improved alternator test that determines whether the alternator belt is slipping using data read using a vehicle data port. Further, the system and method provides a battery bank test that correlates the voltage before and after a load is applied to the battery bank to the batteries&#39; conditions. When testing the starter, the oil temperature is read via the vehicle data port, allowing for a determination of whether the current draw is abnormally high.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Traditionally vehicle electrical systems have been tested with a carbon pile variable load tester and a voltmeter. A carbon pile load tester is a variable load tester that utilizes a pile of carbon disks as a resistive load. As the carbon disks are compressed the resistance is decreased and the current through the tester increases. Carbon pile testers are capable of applying a variable load of several hundreds of amps to a battery or electrical system. To test the batteries on a heavy-duty vehicle with a carbon pile load tester, each battery must be disconnected from the battery bank and tested separately. The tester is connected to the battery posts and the voltage of the battery is read. If the battery voltage is below 12.45 volts, the battery must be charged before proceeding with the test. Once it is determined that the battery has sufficient charge, a load knob on the tester is manually turned by the operator to compress the carbon discs. The carbon disks are compressed until a load of one half the rated cold cranking amps (CCA) is applied to the battery. The load is maintained for 15 seconds. After 15 seconds, the voltage of the battery is noted and the load is removed by uncompressing the carbon disks. The operator then compares the noted voltage to a pass/fail voltage obtained from a chart or graph that compensates for the temperature. Unfortunately, the accuracy of this test is dependent on the skill and care of the operator.  
         [0002]     To test the cables and the connections in the charging or starting circuits of a heavy-duty vehicle with a carbon pile load tester, the tester is connected at the alternator or at the starter. The auxiliary voltage leads of the tester (or the leads of a separate voltmeter) are connected to the battery bank. An operator applies and adjusts a load current equal to the rated output of the alternator or the specified current draw of the starter using the variable load tester. While the current flows, the operator notes the voltage at the alternator or starter and the voltage at the battery bank. The voltage drop of the system is calculated by the operator. If the voltage drop exceeds a specified amount (e.g., 0.5 volts), the electrical system is deemed problematic and the operator must determine if the problem is in the positive or the negative leg of the electrical system. This determination is made by reconnecting the auxiliary voltage leads across the positive leg and reapplying the load. The voltage may not exceed a maximum acceptable voltage drop (e.g., 0.25 volts). A value exceeding one half of the maximum acceptable voltage indicates a possible defect in the positive leg. Next, the auxiliary voltage leads are connected across negative leg of the system, and the load is again applied and adjusted. The voltage across the negative leg is measured. A value exceeding one half of the maximum acceptable voltage (e.g., 0.25 volts) indicates a possible defect in the negative leg.  
         [0003]     Before testing the alternator, the operator should test the battery or batteries, and the cables between the alternator and the battery bank. The operator should make any necessary repairs based on the outcome of these tests. When testing the alternator, the operator connects the load tester to the battery bank and while the vehicle is running, reads the voltage. The alternator should regulate the voltage between approximately 13.2 volts and 14.8 volts on a 12 volt system. If the voltage is not within the specified range, there is a problem with the alternator or the voltage regulator. If the alternator maintains the voltage within the specified range, the operator applies a carbon pile load to the system until the voltage at the batteries is about 12.6 volts. At 12.6 volts the batteries will not be collecting charge or delivering current. At this point, the operator reads the current that the tester is drawing. A DC amplifier probe can also be used to measure the total output of the alternator. If the output of the alternator is within 10% of its rated output, the alternator has passed the test.  
         [0004]     Before an operator tests the starter, the battery or batteries, the cables to the starter from the battery bank and the magnetic switch circuit should have previously been tested and repaired. A magnetic switch is a solenoid type relay that energizes the starter solenoid on the starter when the ignition key is turned to the start position. These tests, however, often do not occur. To test the starter, the operator connects the load tester to the battery bank and monitors the voltage as the engine is cranked. The operator then applies a load to the battery bank until the voltage of the battery bank reaches the voltage that was observed while the engine was cranking. At this point, the operator calculates the current that the tester is drawing. A higher than normal current draw is indicative of a bad starter.  
         [0005]     More recently automated testers have been introduced that make testing quicker and more reliable. These testers, however, still focus on the components of the system and not the system as a whole. Often alternators and starters that are still good are misdiagnosed and removed because of another problem in the electrical system (i.e., weak batteries, corroded/damaged cables, bad connections, or a loose belt)—this is undesirable. If these alternators and starters are under warranty they are sent back to their manufacturer under a warranty claim. The manufacturer tests the unit. Because the units are still properly functioning, the warranty is denied. High costs are incurred in this type of situation. Even after high costs are incurred, the real problem has still not been resolved.  
         [0006]     Because many starting and charging electrical problems are progressive, a good preventative maintenance test is needed to catch and correct these problems before they cause a no-start situation. Additionally, a loose alternator belt can prevent an alternator from outputting full current by not turning the alternator at full speed. Current testers have no way of determining whether the inability of the alternator to output is due to belt slippage. Temperature affects the viscosity of engine oil and the amount of current it takes to crank a starter when the oil is cold is higher than when the oil is warm. Therefore, a system and method for testing a charging and starting system for testing the systems as a whole, for testing for alternator slippage and for testing a starter system incorporating the oil temperature is needed.  
         [0007]     There exists diagnostic tools that connect to a data port of vehicle; these tools are often referred to as scan tools. Typically, the scan tools stand-alone and do not interface with other test equipment. Presently, J1708 or J1587 and J1939 are the protocols used with the data port. Society of Automotive Engineers (SAE) documents outline these protocols. These scan tools, however, fail to provide methods and/or systems for utilizing oil temperature during a starter test and utilizing the RPM readings in determining alternator slippage.  
         [0008]     U.S. Pat. No. 6,650,120 to Bertness et al., U.S. Pat. No. 6,718,425 to Kramptiz, and U.S. Pat. No. 6,777,945 to Pajakowski et al., and U.S. Patent Application 2003/0038637 to Bertness et al. describe testing charging and starting system components, but fail to test the charging and/or starting system systematically and connecting to a vehicle data port.  
         [0009]     U.S. Pat. No. 4,375,672 to Kato et al., U.S. Pat. No. 6,029,512 to Suganuma, and U.S. Pat. No. 6,466,025 to Kiang, and U.S. Application 2003/0155772 to Scherrbacher et al. disclose testing alternators to determine whether they are good. However, these references fail to disclose a system for detecting alternator belt slippage where engine RPM is read via a vehicle data port and alternator rotation is read via an R-terminal.  
         [0010]     U.S. Pat. No. 5,583,440 to Bisher relates to testing and running AC loads on a backup system. The &#39;440 patent, however, fails to test a battery or bank of batteries in a vehicle.  
         [0011]     U.S. Pat. No. 6,316,914 to Bertness relates to testing a bank of batteries using a current sensor. The &#39;914 patent, however, fails to disclose testing a bank of batteries without the use of an inter cell current sensor.  
         [0012]     U.S. Pat. No. 6,351,102 to Troy discloses a method and system for testing vehicular batteries. The &#39;102 patent, however, fails to disclose a method and system for testing a bank of batteries.  
         [0013]     U.S. Pat. No. 6,759,843 to Bertness et al. relates to testing storage batteries. The &#39;843 patent, however, does not disclose testing a vehicle&#39;s bank of batteries.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The invention relates to a systematic method and system for testing the charging and starting systems of a vehicle, which requires each individual test to pass before proceeding. In addition, the invention incorporates an improved alternator test that determines whether the alternator belt is slipping using data read using a vehicle data port. Further, the invention provides a battery bank test that correlates the voltage before and after a load is applied to the battery bank to the batteries&#39; conditions. When testing the starter, the oil temperature is read via the vehicle data port, allowing for a determination of whether the current draw is abnormally high.  
         [0015]     In one aspect of the invention, a method of testing a charging system of a vehicle comprises the steps of testing a bank of batteries of the vehicle; testing cables connecting an alternator to the batteries; testing the alternator; and determining test results of the battery, cable and alternator testing steps.  
         [0016]     In yet another aspect of the invention, a system for testing the starting system of a vehicle comprises a tester apparatus; a plurality of load leads adapted to connect to the components of the starting system; a plurality of voltage leads for connecting to components of the charging system; a data connection cable for connecting said tester to a vehicle data port; and said tester having an circuit for determining the condition of said batteries, said magnetic circuit, cables and said starter.  
         [0017]     In another aspect of the invention, a method for testing a bank of batteries comprises the steps of determining a size of the battery bank via leads connected to said battery bank; measuring a voltage of the battery bank; comparing said measured voltage to a threshold voltage using the cold cranking amps of each battery and temperature; if said measured voltage is greater than said threshold, applying a load to the bank of batteries; measuring the voltage of the bank of batteries while the load is being applied, wherein the voltage change is correlated to the battery bank condition; and determining whether said bank of batteries passes based on said change in voltage.  
         [0018]     In another aspect of the invention, a system for testing the charging and starting system of a vehicle comprises a tester apparatus; a plurality of load leads adapted to connect to the components of the charging and starting system; a plurality of voltage leads for connecting to components of the charging and starting system; a data connection cable for connecting said tester to a vehicle data port; an cable for connecting said tester to an R-terminal on said alternator; and said tester having an circuit for determining the condition of batteries or battery bank, cables, magnetic circuit, said starter and said alternator.  
         [0019]     In another aspect of the invention, an apparatus for testing a starting system of a vehicle comprises means for testing a bank of batteries of the vehicle; means for testing a magnetic circuit of the starting system; means for testing main starting cables of the starting system; means for testing a starter of the vehicle; and means for determining results of the battery, magnetic circuit, cables and starter testing steps.  
         [0020]     In a further aspect of the invention, an apparatus for testing a charging and starting system comprises means for determining whether a test should be run; means for determining the number of batteries in the vehicle; means for determining whether said vehicle has a data port; and means for beginning said test. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a perspective view of an embodiment according to the present invention.  
         [0022]      FIG. 2  is a block diagram of the testing unit shown in  FIG. 1 .  
         [0023]      FIG. 3   a  is a schematic diagram of a circuit illustrating how a SYS_POS output results from a measurement of a voltage across the load leads depicted in  FIG. 1 .  
         [0024]      FIG. 3   b  is a schematic diagram of a circuit illustrating how a SYS_NEG output results from a determination that the load leads depicted in  FIG. 1  are connected in reverse.  
         [0025]      FIG. 3   c  is a schematic diagram of a circuit illustrating how a BUS_VOLTS output results from a measurement of a voltage across large conductors of the load leads depicted in  FIG. 1 .  
         [0026]      FIG. 3   d  is a schematic diagram of a circuit illustrating how a POS_DROP output results from a measurement of a voltage drop across a positive leg of an electrical system.  
         [0027]      FIG. 3   e  is a schematic diagram of a circuit illustrating how a NEG_DROP output results from a measurement of a voltage drop across a negative leg of the electrical system.  
         [0028]      FIG. 3   f  is a schematic diagram of a circuit illustrating how an EXT_POS output results from a measurement of a voltage drop across the voltage leads depicted in  FIG. 1 .  
         [0029]      FIG. 3   g  is a schematic diagram of a circuit illustrating how an EXT_NEG output results from a determination that voltage leads depicted in  FIG. 1  are connected in reverse.  
         [0030]      FIG. 4  is a circuit diagram of a portion of the system of  FIG. 3 , including a microprocessor and its display, keypad and nonvolatile memory.  
         [0031]      FIG. 5  is a circuit diagram of a power supply circuit used in the testing unit of  FIG. 2 .  
         [0032]      FIG. 6  is a circuit diagram of a load circuit used in the testing unit of  FIG. 2 .  
         [0033]      FIG. 7  is a circuit diagram of an analog conditioning and alternating current amplifier/rectifier circuit used in the testing unit of  FIG. 2 .  
         [0034]      FIG. 8  is a sectional view taken transversely through an upper half of the testing unit of  FIG. 1 .  
         [0035]      FIG. 9  is a bottom plan view of a printed circuit board used in the testing unit.  
         [0036]      FIG. 10  is a block diagram illustrating the connections between a vehicle data port, the tester and an alternator.  
         [0037]      FIG. 11 . is a perspective front view of an internal structure of the testing unit of  FIG. 1 , showing a top surface of a printed circuit board and a side wall of a housing.  
         [0038]      FIG. 12  illustrates a schematic diagram of the data port cable of the invention.  
         [0039]      FIG. 13  illustrates an exemplary data port cable firmware of the invention.  
         [0040]      FIG. 14  is a flowchart of an exemplary program executed by the microprocessor to initiate operation of the testing unit.  
         [0041]      FIG. 15  is a flowchart of exemplary processing executed when a system test is selected.  
         [0042]      FIG. 16  is a flowchart of exemplary processing preformed during the battery test.  
         [0043]      FIG. 17  is a flowchart illustrating exemplary steps performed while testing the charging system in accordance with the invention.  
         [0044]      FIG. 18  is a flowchart illustrating exemplary steps preformed during the alternator test in accordance with the invention.  
         [0045]      FIG. 19  is a flowchart illustrating an exemplary embodiment of the starting system test in accordance with the invention.  
         [0046]      FIG. 20  is a flowchart illustrating an exemplary embodiment of the starter test in accordance with the invention.  
         [0047]      FIG. 21  is a perspective front view of an analyzer shown in  FIG. 1  without keys, taken from a lower end of the testing unit of  FIG. 1 .  
         [0048]      FIG. 22  is a sectional view taken transversely through a lower half of the testing unit shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]     In the following detailed description, reference is made to the accompanying drawings, which are a part of the specification, and in which is shown by way of illustration of various embodiments whereby the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments may be utilized, and that structural, logical, and electrical changes, as well as changes in the materials used, may be made without departing from the spirit and scope of the present invention.  
         [0050]     The invention relates to a system and method for testing the charging and starting system of a vehicle. The embodiments of the tester may utilize the same or similar hardware as that described in U.S. Pat. No. 6,771,073, assigned to Auto Meter Products, Inc., which is hereby incorporated by reference. As explained below, in the present invention, the RS-232 port used to connect the testing unit  5  to a computer, may also connect to a J1780 data port on the vehicle being tested. RS-232 is a common type of serial communication port used on many products that communicate with a computer. The tester described in U.S. Pat. No. 6,771,073 is modified to include several new features described herein. The preferred embodiment of this invention utilizes the J1708 data port because it is present on new trucks as well as on many older trucks. The J1939 protocol is present on late model trucks only. It should be noted that the test method and processing of the invention is not limited to the protocol used to read the data.  
         [0051]     In an effort to save time or because of lack of understanding of the interdependence of the components of the starting or charging system, technicians will often attempt to test the alternator or the starter without testing the batteries or cables first, thereby often misdiagnosing that the problems are in the alternator or starter. The present invention addresses the problem of misdiagnosing the functionality of an alternator or starter by providing a technique to ensure that the entire starter or charging system is systematically tested to find the real problem. Furthermore, the present invention provides improved alternator testing by testing for belt slippage; improved starter testing by reading engine oil temperature and comparing the current draw to the acceptable current draw with the oil at the measured temperature; and quicker battery testing by providing a battery bank test.  
         [0052]     Referring to  FIG. 1 , a perspective view of a hand-held testing unit  5  embodying principles of embodiments of the present invention is shown. A bottom front panel  10  includes an On/Off key  11 , a Print key  12 , and a key pad with four manual keys  13 - 16  used in conjunction with a liquid crystal display (LCD)  17 . The four manual keys  13 - 16  include an +/Up key  13 , a −/Down key  14 , an Y/Enter key  15 , and an N/Esc key  16 . The keys  13 - 16  provide input signals to a microprocessor (not shown) that controls operation of the testing unit  5 , including messages and/or data displayed on the LCD  17 . A pair of load leads  18   a  and  18   b , with kelvin clamps  35   a  and  35   b , extend from an end of the testing unit  5  for connection to a starter, alternator, or batteries of an electrical system under test (not shown).  
         [0053]     Each kelvin clamp  35   a ,  35   b  comprises a first jaw  37   a ,  37   b  and a second jaw  38   a ,  38   b , for facilitating connection to the electrical system under test. Furthermore, the pair of load leads  18   a  and  18   b  includes a positive load lead  18   a  and a negative load lead  18   b . Each load lead of the pair of load leads  18   a  and  18   b  also comprise a large conductor (not shown) that carries current when a load is applied and a small conductor (not shown) that is used to measure voltage. The large and small conductors are associated with the first and second jaws,  37   a ,  37   b  and  38   a ,  38   b , respectively, of the kelvin clamps  35   a  and  35   b . Additionally, a pair of voltage leads  20   a  and  20   b  with clamps  36   a  and  36   b , respectively, extend from the testing unit  5  for connection to a battery (not shown) of the electrical system under test. The pair of voltage leads comprise a positive voltage lead  20   a  and a negative voltage lead  20   b . The remaining components of the testing unit  5  will be described below in connection with  FIGS. 8-9 ,  11 , and  21 - 22 .  
         [0054]     Referring now to  FIG. 2  the testing unit  5  is controlled by a microprocessor  20  that receives power from a power supply circuit  21 , which in turn is powered by a lead-acid battery/system B under test. A 9-volt battery  22  provides an alternative power source when the testing unit  5  is not connected to the battery B. The microprocessor  20 , which also includes an analog-to-digital (A/D) converter  27 , receives input signals from the four manual keys  13 - 16 , an analog conditioning circuit  23 , and an alternating current (AC) amplifier/rectifier circuit  24 , as will be described in more detail below.  
         [0055]     The microprocessor  20  provides output signals to a liquid crystal display (LCD)  17  for communicating with a user, an infrared printer port  25  for printing results, to a serial port  26  for communicating with an off-board computer  26   a , such as, for example, a personal computer, a load circuit  28  that can be connected to the battery/system B under test, and to an audio buzzer  30  for providing audible alarms or signals. 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. The microprocessor  20  also receives information from the vehicle data port  266 .  
         [0056]     In one exemplary embodiment, flash memory maybe used as the nonvolatile memory  29 . The use of flash or other removable nonvolatile memory allows for the testing units  5  to be customized for each user&#39;s implementation. For example, the batter policy may be stored within the nonvolatile memory  29  so that the technician using the testing unit  5  will not be required to remember the battery policy, thereby decreasing the possibility of human error.  
         [0057]     The following description describes one embodiment of circuitry used within testing unit  5 . It should be appreciated that the invention is not limited to the value of the resistances, capacitors and other unit-values described. Referring now to  FIG. 3   a , there is shown a schematic diagram of a circuit illustrating how an output voltage (SYS POS)  810  results from measurement of a voltage across the load leads  18   a  and  18   b  depicted in  FIG. 1 . The circuit is arranged in a differential amplifier configuration, such that a voltage difference between VOLTS+ 811  and VOLTS−  812  (wherein VOLTS+  811  and VOLTS−  812  indicate the voltage at the positive and negative load leads  18   a  and  18   b , respectively), preferably with an input range of 0-15.36 volts, produces a gain of less than one. In a desired embodiment, two 187 KΩ resistors  802  and  803 , and two 49.9 KΩ resistors  805  and  806  are arranged with an operational amplifier  807  in the differential amplifier configuration to set the gain of the operational amplifier  807 . A 2 KΩ resistor  808  is coupled with a 1 microfarad capacitor  801  to form a low-pass filter in order to reduce system noise. A diode  809  is included in the circuit to detect a reverse connection of VOLTS+  811  and VOLTS−  812  and also to prevent transmission of a voltage below 0.3 Volts to the A/D converter  27  of the microprocessor  20 . The SYS_POS output voltage  810  is input into the microprocessor  20 .  
         [0058]     Referring now to  FIG. 3   b , there is shown a schematic diagram of a circuit illustrating how a positive output voltage (SYS_NEG)  820  results from a determination that the load leads  18   a  and  18   b  of  FIG. 1  have been connected in reverse. An inverting amplifier  823  reads a voltage from VOLTS+  811  and converts the voltage of VOLTS+  811  to a positive signal ranging from 0 to 4.096 Volts. This positive signal is filtered by a low pass filter comprising a 2 KΩ resistor  824  and a 1 microfarad capacitor  826 . The SYS_NEG output voltage  820  is then sent to the A/D converter  27  (not shown) and an indication of a reversed connection of the load leads  18   a  and  18   b  is displayed on the LCD  17 . Thus, the circuit of  FIG. 3   b  uses an inverting amplifier  823  to send a positive voltage to the A/D converter  27  if the load leads  18   a  and  18   b  are connected in reverse.  
         [0059]     Referring now to  FIG. 3   c , a schematic diagram of a circuit illustrating a measurement of a voltage across the large conductors of the load leads  18   a  and  18   b  resulting in an output voltage (BUS_VOLTS)  830  indicative of a measured voltage across the large conductors is shown. An operational amplifier  834  is arranged in a voltage-follower configuration and a pair of resistors  832  and  833  are arranged to create a voltage divider circuit. The voltage divider/voltage follower combination measures a voltage (BUS+  838 ) across the large conductors of the load leads  18   a  and  18   b.    
         [0060]     The microprocessor  20  of  FIG. 2  compares the BUS_VOLTS output voltage  830  to the SYS_POS output voltage  810  of  FIG. 3   a , in order to ensure that a proper connection has been made at the load leads  18   a  and  18   b . A difference between the SYS_POS output voltage  810  and the BUS_VOLTS output voltage  830  that is greater than a value pre-programmed in the microprocessor  20  indicates a poor connection of the kelvin clamps  35   a ,  35   b  shown in  FIG. 1 .  
         [0061]     Referring now to  FIG. 3   d , depicting a schematic diagram of a circuit illustrating how a positive leg output voltage (POS_DROP)  840  results from a measurement of a voltage drop across a positive leg of the electrical system. Two voltage dividers, each preferably comprising a 4.22 KΩ resistor and a 649 KΩ resistor ( 842 / 845  and  843 / 846 , respectively) divide input signals EXT+  854  (a voltage at the positive voltage lead  20   a  of voltage leads  20   a  and  20   b ) and VOLTS+  811  to an operational amplifier  849 , such that input signal EXT+  854  and input signal VOLTS+  811  is maintained within a common-mode range of the operational amplifier  849 .  
         [0062]     The input signals EXT+  854  and VOLTS+  811  are then sent through a differential amplifier circuit  839 , which includes two 332 KΩ resistors  844  and  847 , two 4.99 MΩ resistors  848  and  855 , and the operational amplifier  849 . The differential amplifier circuit  839  measures a difference between EXT+  854  (i.e., a voltage at the positive voltage lead  20   a ) and VOLTS+  811  (i.e., a voltage at the positive load lead  18   a ). Thus, the input signals EXT+  854  and VOLTS+  811  are first divided, and then amplified.  
         [0063]     A 412 KΩ resistor  841  is incorporated into the circuit to ensure a positive offset by the operational amplifier  849  so that the offset can be calibrated out in software. A signal output by the differential amplifier circuit  839  is then passed through a low-pass filter comprising a 2 KΩ resistor  852  and a 1 microfarad capacitor  853  and the resulting POS_DROP output voltage is transmitted for analysis to the microprocessor  20 .  
         [0064]     Referring now to  FIG. 3   e , illustrating a schematic diagram of a circuit depicting how a negative leg output voltage (NEG_DROP)  860  results from a measurement of a voltage drop across a negative leg of the electrical system. The difference between VOLTS−  812  (i.e., a voltage at the negative load lead  18   b ) and EXT−  859  (i.e., a voltage at the negative voltage lead  20   b ) is measured. The schematic diagram is configured similarly to that of  FIG. 3   d , however, unlike the schematic diagram of  FIG. 3   d , a voltage divider is unnecessary since both VOLTS−  812  and EXT−  859  inputs are maintained at a value close to ground. The VOLTS−  812  and EXT−  859  are transmitted through a differential amplifier circuit  865   a  comprising two 100 KΩ resistors  861  and  863 , two 200 KΩ resistors  864  and  866 , and an operational amplifier  865 . A signal transmitted through the differential amplifier circuit  865   a  is sent through a low-pass filter, which comprises a 2 KΩ resistor  867  and a 1 microfarad capacitor  869 . A NEG_DROP output voltage resulting therefrom is sent to the microprocessor  20 .  
         [0065]     Referring now to  FIG. 3   f , illustrating a schematic diagram of a circuit depicting how a voltage lead output (EXT_POS)  870  results from a measurement of a voltage drop across the voltage leads  20   a  and  20   b  shown in  FIG. 1 . In a similar fashion to the schematic diagram illustrated in  FIG. 3   a , the circuit of  FIG. 3   f  incorporates a differential amplifier circuit  876   a , which includes two 187 KΩ resistors  872  and  873 , two 49.9 KΩ resistors  874  and  875 , and an operational amplifier  876 . The differential amplifier circuit  876   a  reads input voltages EXT+  854  and EXT−  859 , which correspond to voltages of the voltage leads  20   a  and  20   b , respectively, and transmits an output signal. A gain of less than one is produced by the differential amplifier circuit  876   a . An output signal transmitted by the differential amplifier circuit  876   a  is then sent through a low-pass filter comprising a 2 KΩ resistor  877  and a 1 microfarad capacitor  879 . The diode  878  prevents transmission of a voltage of less than 0.3 Volts in the event that the inputs EXT+  854  and EXT−  859  are connected in reverse. The EXT_POS output voltage  870  is input into the microprocessor  20 .  
         [0066]     Referring now to  FIG. 3   g , depicting a schematic diagram of a circuit illustrating how a reversely-connected voltage lead output (EXT_NEG)  880  results from a determination that the voltage leads  20   a  and  20   b  of  FIG. 1 , have been connected in reverse. The schematic diagram of  FIG. 3   g  is similar to the circuit illustrated in  FIG. 3   f , with the exception that the EXT+  854  and EXT−  859  input voltages (i.e., the voltages of the positive and negative voltage leads  20   a  and  20   b , respectively) are reversed. The reversal of the EXT+  854  and the EXT−  859  inputs, in combination with a diode  888 , allows for detection of a reverse hookup.  
         [0067]     Referring now to  FIG. 4 , which illustrates a more detailed diagram of the testing unit  5  shown in  FIG. 2 . The microprocessor  20 , which includes the A/D converter  27 , receives an ON/OFF signal  21   a  from the power supply circuit  21  of  FIG. 2 , an ON_SW signal  11   a  from the On/Off key  11  shown in  FIG. 1 , KEY  1 - 4  signals  13   a - d  from the four manual keys  13 - 16  shown in  FIG. 1 , and a signal from the Print key  12  via a pull-up resistor network  31 . Also received by the A/D converter  27  is an AC_VOLTS output  37  from the AC amplifier/rectifier circuit  24 , the SYS_POS output voltage  810 , which measures the voltage across the load leads  18   a  and  18   b , the SYS_NEG output voltage  820 , the BUS_VOLTS output voltage  830 , the POS_DROP output voltage  840 , the NEG_DROP output voltage  860 , the EXT_POS output voltage  870 , the EXT_NEG output voltage  880 , and data signals from the non-volatile memory  29 . 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 , are also input into the A/D converter  27  of the microprocessor  20 .  
         [0068]     Output signals produced by the microprocessor  20  include: display-generating signals to the LCD  17 , which also receives Vcc.sub. 1  at terminal  2  of the LCD  17  and a reduced Vcc.sub. 2  at terminal  3  of the LCD  17  to set a LCD contrast (the reduction being achieved by a voltage divider formed by a pair of resistors R 2  and R 3  connected between Vcc.sub. 2  and ground, with terminal  3  of the LCD  17  receiving a voltage that exists between resistors R 2  and R 3 ); a POWER signal  21   b  for the power supply circuit  21  shown in  FIG. 2 ; a PRINTER signal  19  for an infrared transducer used to communicate with the printers; switching signals LOAD 1   34   a , LOAD 2   34   b , LOAD 3   34   c , and CCA_LOAD  34   d  supplied via pull-down resistors  32  and current-limiting resistors  33 , to control Field Effect Transistors (FETs) that connect and disconnect various loads to the battery/system B under test; and data signals to be stored in the non-volatile memory  29 .  
         [0069]     Coupling to a printer is effected by an infrared coupling diode  99  mounted in an upper end of the testing unit  5  (as also shown in  FIG. 1 ). The PRINTER signal  19  from the microprocessor  20  is supplied via a 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.  
         [0070]     Referring now to  FIG. 5 , illustrating a circuit diagram that depicts in more detail the power supply circuit  21  shown in  FIG. 2 . The BUS+input  838  to the power supply circuit is connected to battery/system B under test via the large conductor of the positive load lead  18   a , while ground is connected to the large conductor of the negative load lead  18   b . The supply current from the BUS+  838  input (indicative of the voltage across the large conductors of the load leads  18   a  and  18   b ) passes through a blocking diode D 10  and a resettable fuse F 1  that trips under high currents, which resets after a period of time. The diode D 10  prevents damage to the testing unit  5  if the load leads  18   a  and  18   b , connected to the battery/system B under test, are connected in reverse. When the load leads  18   a  and  18   b  are not connected to the battery/system B under test, the power supply circuit  21  is powered by a 9-volt battery  22  (also shown in  FIG. 2 ) through a blocking diode D 1 .  
         [0071]     The power supply circuit  21  is turned on by the ON_SW signal  11   a  from the On/Off key  11  ( FIG. 1 ), and then is kept on by the POWER signal  21   b  (also shown in  FIG. 4 ) output by 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 ON_SW signal  11   a  is applied to a 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  21   a  (also shown in  FIG. 4 ) connected 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 signal  21   a  to ground. The POWER signal  21   b  from the microprocessor  20  is supplied to the base of the switching transistor T 11  through a current-limiting resistor R 14 .  
         [0072]     A low voltage at a collector of either transistor T 10  or T 11  turns on FET  10 , which then supplies current from the BUS+ input  838  to the input terminal of a voltage-regulating IC  108  to switch on the power. A 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  108  to ground. The output of the IC  108  is connected to a terminal Vcc.sub. 3  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.sub. 3  to ground. A voltage divider is formed by a pair of resistors R 16  and R 17  to supply a desired voltage level to an “adjusted” output of the IC  108 . The voltage level V in  that exists between the resistor R 10  and the fuse F 1  is supplied to the four manual keys  13 - 16  of  FIG. 1 .  
         [0073]     The power supply circuit can be turned off by the microprocessor  20  by sending a low signal to the POWER signal  21   b  after the On/Off key  11  has been pressed or after the testing unit  5  has been on for two minutes with no activity. When the On/Off key  11  is pressed while the power supply is on, the resulting change in the ON_SW signal  11   a  is sensed by the microprocessor  20 , which responds by producing a low POWER signal  21   b . This turns off the transistor T 11 , which turns off the power supply.  
         [0074]     Referring now to  FIG. 6 , illustrating a circuit diagram of the load circuit  28 . The load circuit  28  comprises three parallel resistors R 21 , R 22  and R 23 , each of which can be connected to the battery/system B under test by its own separate signal LOAD 1   34   a , LOAD 2   34   b , or LOAD 3   34   c  which turns on a corresponding switching FET  21 ,  22  or  23 , so that current can flow from the battery/system B under test 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 load circuit  28  is connected to the battery/system B under test when it is desired to load test the battery/system B to evaluate its condition.  
         [0075]     Referring now to  FIG. 7 , illustrating the analog conditioning circuit  23  and the AC amplifier/rectifier circuit  24  of  FIG. 2 . The analog conditioning circuit  23  is connected to terminals or posts of the battery/system B under test for measuring voltage across these posts. The connections to the battery/system B terminals are made with kelvin clamps  35   a  and  35   b  on the ends of the load leads  18   a  and  18   b  extending from the lower end of the testing unit  5 . The VOLTS+  811  input to the analog conditioning circuit  23  is derived from the small conductor of the positive load lead  118   a , while the VOLTS−  812  input is derived from the small conductor of the negative load lead  18   b . A pull-down resistor R 40  is connected between the two load leads  18   a  and  18   b.    
         [0076]     The VOLTS+  811  and VOLTS−  812  inputs are connected to the positive and negative inputs of an operational amplifier  40  via gain-setting resistors R 41 -R 44  in a differential amplifier configuration. An output of the operational amplifier  40  furnishes the analog SYS_POS output voltage  810  (also shown in  FIG. 3   a ) that represents an output voltage measuring voltage across the load leads  18   a  and  18   b . This SYS_POS output voltage  810  is one of the inputs to the microprocessor  20  and its internal A/D converter  27 .  
         [0077]     Still referring to  FIG. 7 , the SYS_POS output voltage  810  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 a magnitude of any AC ripple in the battery voltage. (An AC ripple is associated with an AC component of the DC voltage derived from the battery, and typically originates from the alternator.) 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 operational amplifier  41  is connected to a pair of rectifying diodes D 40  and D 41 , which prevent a negative voltage from going into the microprocessor  20  and its internal A/D converter  27 . An integrating capacitor C 41  is connected in parallel with the two diodes D 40  and D 41 , and a lowpass filter comprising a resistor R 48  and a capacitor C 48  is included to filter the signal. The resulting DC output of the AC amplifier/rectifier circuit  24  furnishes an AC_VOLTS output  37  that represents the magnitude of an AC ripple and is one of the inputs to the microprocessor  20 .  
         [0078]     Referring now to  FIG. 8 , illustrating a sectional view of the upper half of the tester. Structurally, the testing unit  5  of  FIG. 1  includes a strong, durable housing formed by a pair of extruded aluminum side members  80  and  81  (see  FIGS. 1, 22 ,  8 , and  21 ) 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 ). Interior surfaces of the two side members  80 ,  81  form a first set of elongated slots  85  and  86  ( FIG. 22 ) 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  of the load circuit  28  (of  FIG. 6 ) 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. 8 ). A third plate  90  extends across the upper end of the printed circuit board  87  and overlaps the lower ends of the insulating mounting plates  88  and  89 . The insulating 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 the battery/system B under test.  
         [0079]     Referring now to  FIGS. 9 and 11 , illustrating the printed circuit board  87  carrying two rows of TO- 220  packaged devices, including switching transistors FET 10 , FET 20 , FET 21 - 23 , a voltage regulator  100 , and diodes D 21 -D 26 , mounted along opposite edges of the printed circuit 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. 18 ) to assist in dissipating heat from the components, especially when the load circuit  28  (of  FIG. 2 ) is utilized.  
         [0080]     The load leads  18   a  and  18   b  that connect the testing unit  5  to the battery/system 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. 9 . 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 load leads  18   a  and  18   b . These copper plates  96  and  97  permit the use of small components such as the TO- 220  packaged devices, despite the high current levels.  
         [0081]      FIG. 10  illustrates an embodiment depicting the hardware of the data cable  410  of the invention. The cable hardware  410  is controlled by a micro-controller  400 . The micro-controller communicates with the data port  407  of a vehicle via a cable driver  405  (shown as a J1708 driver) and with the testing unit  5  via the RS232 driver  402 . The micro-controller  400  also reads the signal from the R-terminal  404  of the alternator after the signal has been conditioned by signal conditioning block  401  to be in the voltage and frequency range of the micro-controller  400 . The micro-controller  400  and other electronics on the data cable  410  receive power from the power supply  406 , which, in turn, is powered from the battery system B voltage via the data port  407 .  
         [0082]      FIG. 12  illustrates a schematic of an exemplary embodiment of the data cable  410  of the invention. The micro-controller  400  labeled U 1  is located in the center of the schematic. The J1708 driver  405  includes U 4  (a commercially available J1708 driver) and the resistor/capacitor network consisting of resistors R 101 , R 102 , R 103 , R 104 , and capacitors C 102  and C 103 . This is a common exemplary network arrangement used when interfacing to a data port  410 . The four connections to the data cable are VPP, {overscore (DO)}/{overscore (RI)}, DO/RI, and ground denoted by the ground signal. The power supply  406  comprising U 3  (a common voltage regulator), resistor R 111 , and capacitors C 101  and C 105  receives power via the VPP and ground connections of the data port  407 . Resistor R 111  drops the voltage so that less power is dissipated in the voltage regulator U 3 . Capacitors C 101  and C 105  are filter capacitors. The RS-232 driver  402  includes U 2  (a commercially available RS-232 driver) and resistors R 105  and R 106 . Resistors R 105  and R 106  limit the current and protect the RS-232 driver  402  in the event of a connection error or short circuit. The signal conditioning circuitry  401  for the signal from the R-terminal includes resistor R 109 , R 110  and capacitor C 104 . Resistors R 109  and R 10  form a voltage divider to attenuate the signal. Capacitor C 104  in conjunction with R 110  form a low pass filter that filters out high frequency noise. Resistor R 107  connects the ground of the cable to the ground of the testing unit  5  via the RS-232 port. Resistor R 107  prevents high current from flowing through the cable when the ground, on the vehicle, is faulty. U 5  (part HDR1X6) allows a programmer to connect to the micro-controller  410  in order to program it during manufacturing.  
         [0083]      FIG. 13  illustrates an exemplary operation of the data cable  410  firmware. The firmware for the data cable  410  first initializes internal variables and hardware (step  200 ), which is common in the art of micro-controller programming. Next, in steps  202 ,  205 ,  212  and  214 , the firmware enters a loop where it checks if it is time to poll data on the data port (step  202 ), if a message has been received from the data port  407  (step  205 ), if a character has been received on the RS-232 port (step  212 ), if there has been an overflow or an error condition (step  214 ) and then repeats the loop. If it is time to poll data (step  202 ), the firmware sends out a request on the data port  407  (step  204 ). If a message has been received on the data port  407  (step  205 ), the firmware will process the message and extract the data from the message (step  206 ). After the message has been processed, if the relay flag is set (step  208 ), the controller will relay or send the message via the RS-232 port (step  210 ) and return to the main loop. This loop (steps  205 ,  206 ,  208 ,  210 ) is mainly for troubleshooting and viewing activity.  
         [0084]     In the illustrated embodiment, if a character has been received on the RS-232 port (step  212 ), the firmware will check to see if the character is one of the command characters (“&gt;”, “?”, “:”, “+”, “−”) in steps  216 ,  220 ,  220 ,  224 ,  228  and  232 . If the character is determined to be a “&gt;” character (step  216 ), the firmware sends out the header identifying the data (step  218 ). If the character is a “?” (step  220 ), the firmware will send out the data in ASCII format (step  222 ). If the character is a “:” (step  224 ), the firmware will send out the data in binary format (step  226 ). If the character is a “+” (step  228 ), the firmware will set the relay flag (step  230 ). And if the character is a “−” (step  232 ), the firmware will reset the relay flag (step  234 ). The only character that the testing unit  5  sends to the cable is the “:” which requests the data in binary format (step  226 ). The other characters are used for trouble shooting and for monitoring the data and J1708 communications via a laptop or other PC. When connected to a laptop or PC, “&gt;” can be used to display what each data value corresponds to, “?” can be used to display the current data values. “+” and “−” are used to enable and disable viewing of all J1708 data port activity, respectively. The final check in the loop is for errors or character buffer overflow on the data port  407  (step  214 ). If there has been an error or a buffer overflow the firmware reinitializes and starts the loop over again. Reading from and writing to the RS-232 serial communication port and reading from and writing to the data serial communication port and reading the frequency on the R-terminal input are performed by interrupts using techniques that are well known in the art.  
         [0085]     As previously noted in a preferred embodiment, the testing unit  5  is operated with six keys denoted On/Off, Print, +/Up, −/Down, Y/Enter, and N/Esc. The unit is turned on by pressing the On/Off key and then turned off at anytime by pressing the On/Off key again.  
         [0086]      FIG. 14  illustrates a flowchart depicting an exemplary software implementation on the above described testing unit  5  executed by the microprocessor  20 , which is initiated when the microprocessor  20  detects that the power supply has been turned on. Referring also to  FIG. 1 , the first step  100  displays an introductory message on the LCD  17 , informing the user to select “Y/Enter” to obtain a menu of options. If, at step  103 , the “Y/Enter” key  15  is not pressed within a time-out interval measured by the microprocessor  20  or the On/Off key  11  is pressed, the system powers down, as indicated at step  104 . If, at step  101 , the Y/Enter key  15  is pressed, the program advances to step  102 , where a menu is displayed to provide the user with an array of options. The options include testing the charging cables, starting main cables, magnetic switch circuit, alternator, battery, system, v-drop, and starter. Additional tester options include download, review/print, about, J1708 data, and setup. These options respectively correspond to subroutines  110 - 115 , and  1000 - 1006  shown in  FIG. 14 .  
         [0087]     Whenever the menu is displayed at step  102 , the testing unit  5  waits for the user to select one of the options by pressing e.g., the +/Up key  13  or −/Down  14 , to scroll to the desired option, and then pressing the Y/Enter key  15 . Each selection calls one the routines  110 - 115  or  1000 - 1004 . If, at step  105 , it is detected that no option has been selected within a time-out interval measured by the microprocessor  20 , or if the On/Off key  11  is pressed, the menu  102  is exited at step  106  and the testing unit powers down. The menu  102  may also be exited at  107 , by pressing the N/Esc key  16  at any time during display of the introduction at step  100  or the options menu at step  102 .  
         [0088]     Any test results that are stored in memory, can be reviewed and printed by selecting the Review/Print menu item. The +/Up key  13  and the −/Down key  14  are used to scroll through the data. The Print key  12  is pressed to print the data via the infrared (IR) printer port.  
         [0089]     When J1708 data is selected from the menu, real-time data is transferred from the vehicle to the testing unit  5  via the data cable  410  and is displayed on the screen. Two different screens of data can be displayed by pressing the +/Up  13  or −/Down  14  keys. The setup feature is used to configure the testing unit  5 , set the time and date, and delete unwanted stored test results. The download option is used to download the stored test results and data to a PC via the RS-232 port. The About option displays the software version and copyright notice.  
         [0090]      FIG. 15  illustrates exemplary processing for carrying out a system test  1002 . When the system test  1002  is selected from the main menu  102 , and if a system test sequence was previously started but not completed (step  600 ), the testing unit  5  will prompt the operator to determine if the previous test sequence should be continued (step  622 ). If the previous test sequence is to be continued, the testing unit  5  will determine if the data cable or port was used (step  624 ). The previous test status and whether the data cable/port was used is stored in electrically erasable programmable read only memory (EEPROM) on the testing unit  5 . If the data cable  410  was used (step  624 ), the testing unit  5  will prompt the operator to attach the cable  410  (step  612   a ). Once the data cable  410  is attached, the testing unit  5  prompts the operator to turn the ignition on (step  614   a ). After the engine has been started at step  614   a , the data cable  410  reads data from the data port  407  (step  616   a ) and the testing unit  5  displays the data (step  618   a ). In one embodiment, in order to continue the operator presses the Y/Enter key  15 . If the data cable was not used in the previous test (step  624 ), the testing unit  5  skips to the next test that has not passed (step  620 ).  
         [0091]     At step  602 , if the previous test sequence is not to be continued, the testing unit  5  prompts the operator to select the system to test. The operator may choose to test the battery, charging, or starting system. At step  604  the operator is prompted to select the number of batteries in the system. In a preferred embodiment, the operator is prompted, at step  606 , to enter a vehicle ID number and technician number. At step  608 , the operator is prompted to select whether the vehicle has a data port  407 . If the vehicle does not have a data port  407 , then the testing unit  5  skips to the selected system test (step  610 ). If the vehicle has a data port  407 , the unit will prompt the operator (steps  612  and  614 ) to attach the data cable  410  and turn the ignition on. The data cable  410  reads the data from the data port  407  (step  616 ) and displays the data on the screen (step  618 ). In a preferred embodiment, the operator presses the Y/Enter key  15  to continue on to the selected test.  
         [0092]     In  FIG. 14 , if the battery system is to be tested, the testing unit  5  will proceed to the battery bank test  1001 . If the battery bank test passes, then the battery system test is finished, otherwise each battery is tested separately. If the charging system test is selected, the testing unit  5  will first perform a battery bank test  1001  and if the battery bank test fails, each battery is tested separately. Once the batteries are determined to be good, the charging cables  110  are tested. After the cables are determined to be good, the unit  5  tests the alternator  1000 . In the starting system test  1006 , a battery bank test  1001  is performed first. If the battery bank test fails, each battery is tested separately. After all of the batteries are determine to be good, the magnetic circuit is tested  112 , followed by the starter main cables  111 . Only after the batteries, magnetic circuit and started cables are determined to be good (i.e., passed their respective tests), the starter  1004  is tested. The battery test preformed on the individual batteries when the bank test fails is described in U.S. Pat. No. 6,359,442, hereby incorporated by reference.  
         [0093]      FIG. 16  illustrates exemplary processing preformed to a bank of batteries. The battery bank  1001  test begins by prompting the operator to connect the large tester leads  18   a ,  18   b  to the battery bank (step  700 ). If the testing unit  5  is setup to require battery date codes, the testing unit  5  prompts for the battery date code to be entered (step  702 ). If the vehicle ID number and technician number have not previously been entered (step  704 ), and the testing unit  5  is setup to require them, the testing unit  5  prompts for the ID number and technician number to be entered (step  706 ). In the event that voltage ripple is detected on the large leads in step  708 , the testing unit  5  prompts the operator to turn off the engine (step  710 ). When the engine is off and the ripple has decreased, the testing unit  5  determines if the battery bank is a 24-volt bank (step  712 ). After it is determined that the bank is a 24-volt system, the operator is prompted to test each battery separately (step  714 ). However, if the bank is a 12-volt bank, the operator will be prompted to enter the temperature and the CAA of an individual battery (step  718 ). The bank of batteries is tested to determine whether a minimum voltage is met (step  720 ). If the minimum voltage is met, the testing unit  5  will then load and test the bank to determine the condition of the bank. The battery condition results will be logged at step  722 . If the bank passed the test, the results are displayed and the battery bank test  1001  is complete. If the bank did not pass at step  724 , the operator is instructed to test each battery separately (step  714 ). To perform the individual battery tests, each battery is disconnected from the bank and tested. When it is determined that a battery is bad or low, it must be recharged or replaced and then tested again.  
         [0094]     Before the load is applied, the voltage of the battery bank is tested in step  720  and if the voltage is above a minimum amount (i.e. 12.40 V), the unit applies the load to the battery bank at step  722 . However, if the voltage is not above the minimum value, the batteries must be disconnected and tested separately. At the end of the load period, the unit measures the loaded voltage and subtracts it from the beginning voltage thereby calculating the voltage drop. The unit computes the maximum allowed drop at the given temperature for a two, three, or four battery bank and compares the voltage drop to the maximum allowed. If the drop exceeds the maximum allowed, the batteries must be tested separately, otherwise the bank passes the test.  
         [0095]     The maximum allowed change in voltage for a two-battery bank is given by the formula: 0.90+(70−Temperature)×0.27. The maximum allowed change in voltage for a three-battery bank is given by the formula: 0.75+(70−Temperature)×0.23. The maximum allowed change in voltage for a four-battery bank is given by the formula: 0.60+(70−Temperature)×0.18. A similar formula would be constructed for testing a single remote battery. The formula is based on a temperature measured in degrees Fahrenheit.  
         [0096]      FIG. 17  illustrates the processing steps and the desired order for the steps for testing the charging system in accordance with the invention. The first test conducted in the charging system is of the bank of batteries  1001 . Once the battery bank or the separate batteries have been determined to be good (i.e., pass) in step  1001 , the charging cables are tested  110 . The test conducted on the charging cables  110  is described in U.S. Pat. No. 6,771,073, hereby incorporated by reference. After it is determined that the charging cables are good, the alternator is tested  1000 . Finally, the data is logged and the results are displayed in step  1110 . The results include the condition of the alternator and whether the batteries and cables passed or were repaired.  
         [0097]      FIG. 18  illustrates a flowchart of the exemplary processing preformed during the alternator test  1000 . The alternator test  1000  is the final test run when testing the charging system, however, the test  1000  can also be selected from the main menu as its own test. The alternator test  1000  begins by prompting the operator to perform a visual inspection of the alternator belt, cables and connections (step  902 ). The operator is instructed to connect the leads to the alternator (step  904 ). Next, if not previously entered, at steps  906  and  908  the testing unit  5  prompts the operator to enter a vehicle ID number and a technician number (in a preferred embodiment of the invention). If the ID and technician number were previously entered, the testing unit  5  retrieves the information from EEPROM (at either step  906  or  908 ). The testing unit  5  also prompts the operator to enter the rated output of the alternator (step  910 ). The testing unit  5  determines whether or not the vehicle has a data port  407  by checking EEPROM or by prompting the operator (step  912 ).  
         [0098]     If the vehicle does not have a data port  407  (step  912 ), the testing unit  5  determines if the engine is running by reading the voltage ripple at the alternator. If ripple is detected, the engine must be running. However, if no ripple is detected, the operator is prompted to start the engine (step  916 ). After it is determined that the engine is running, the operator is instructed to idle the engine at about 1000 RPM (step  924 ). In step  930 , the testing unit  5  displays the voltage at the alternator and instructs the operator to allow the voltage to stabilize, once the voltage has stopped rising the operator is to press the Y/Enter key  15 .  
         [0099]     However, if it is determined at step  912  that the vehicle has a data port  407 , the testing unit  5  prompts the operator to attach the data cable  410  and turn the ignition on (steps  914  and  916 ). At this point, the data cable reads data from the vehicle&#39;s engine control unit (ECU) and the unit reads the data from the cable and displays it on the LCD screen (step  918 ). After the data is displayed, the operator is prompted to connect the R-Clip to the R-Terminal of the alternator (step  920 ). The R-terminal is a terminal on most heavy-duty alternators that outputs a square wave that has a frequency proportional to the rotational speed of the alternator. The testing unit  5  determines if the engine is running and if it is not, the testing unit prompts the operator to start the engine (step  922 ). Once the engine is running, the operator is instructed to idle the engine at about 1000 RPM (step  924 ). The testing unit  5  determines if the R-Clip is reading and reports an error if it is determined that the R-Clip is not reading (steps  926  and  928 ). The voltage at the alternator is displayed and the testing unit  5  instructs the operator to allow the voltage to stabilize, and to press the Y/Enter key  15  once the voltage has stopped rising in step  930 .  
         [0100]     After the user presses the Y/Enter key  15 , both with the data cable  410  connected or without, the testing unit  5  determines whether the alternator is a 12-volt or a 24-volt alternator by reading the voltage (step  932 ). For a 24-volt alternator, the testing unit  5  prompts the operator to turn on accessory loads to load the alternator (step  950 ). The engine is revved to a governed speed and the ripple and voltages are read (steps  952  and  941 ). After each reading of the ripple and voltages, the load is removed (steps  951 ,  953 . The voltage is monitored for 10 seconds, the results are logged and the data is displayed (steps  943 ,  945  and  947 ). In the hand-held embodiment of this invention, the testing unit  5  does not load a 24-volt alternator because additional or larger load elements would be required. In a larger embodiment, the testing unit  5  could automatically load the 24-volt alternator.  
         [0101]     However, if the alternator being tested is a 12-volt alternator, the unit  5  automatically loads the alternator and reads the ripple and voltage (step  936 ) and then the load is removed (step  939 ). After the accessory loads are turned on or automatically loaded, the operator is prompted to rev the engine to governed speed for 10 seconds (step  938 ). The testing unit  5  reads the ripple and voltage produced by the alternator and then monitors the voltage for the 10 seconds (steps  942  and  944 ). The peak voltage is recorded. The testing unit  5  logs the data and displays the results (steps  946  and  948 ).  
         [0102]     The data that may be collected and logged during the alternator test includes: rated alternator output, beginning voltage, loaded voltage, peak voltage at governed speed, ripple at idle, ripple at governed speed, R-Terminal frequency at idle (from cable), R-Terminal frequency at governed speed (from cable), engine RPM at idle (from ECU via the data port), engine RPM at governed speed (from ECU via the data port), time, date, vehicle ID, vehicle VIN (from ECU via the data port) and technician number.  
         [0103]     From the data collected during the alternator test, several different determinations regarding the condition of the alternator can be made. For example, if the beginning voltage is below the minimum allowed voltage (e.g., 13.2V on a 12-volt system), the testing unit  5  reports that the alternator has low regulation. Or, if the peak voltage at governed speed is above the maximum allowed voltage (e.g., 14.8V on a 12-volt system), the unit  5  reports that the alternator has high regulation. Otherwise the testing unit  5  reports that the regulation is good. Additionally, if the ripple at idle is above the maximum allowed (e.g., 0.35 VAC for a 12-volt system) or if the ripple at idle is above a lower maximum allowed (e.g., 0.25 VAC for a 12-volt system) and increased to be over another maximum allowed (e.g., 0.26 VAC for a 12-volt system) at governed speed, the testing unit  5  reports that the alternator has a bad diode. When the loaded voltage is below the minimum allowed voltage (e.g., 12.9V for a 12-volt system), the testing unit  5  reports that the alternator has low output.  
         [0104]     If the data port  407  was used during the alternator test and the ratio of the engine RPM to the R-Terminal frequency at governed speed is greater than the ratio of the engine RPM to the R-Terminal frequency at idle by more that a set amount (e.g., 5%), the unit  5  reports that the alternator belt is slipping. Only when it is determined that the regulation is good, the ripple is low, the belt is not slipping and the output is good does the unit reports that the alternator is good.  
         [0105]      FIG. 19  illustrates exemplary tests that must be completed to carry out the starting system test  1006  in accordance with the invention. In testing the starting system  1006 , several components must pass before the starter itself is tested. First, the bank of batteries is tested  1001 . If the battery bank fails, the batteries are tested individually and each must be determined to be good. After the batteries have passed, the magnetic circuit is tested  112 . The test  112  is based on the test described in U.S. Pat. No. 6,771,073, hereby incorporated by reference. However, a select starter function has been added to account for a new gear reduction starter that requires the magnetic circuit to handle 350 amps instead of only 80 amps. Once the magnetic circuit has passed, the starter main cables are tested  111 . After it is determined that the starter main cables are good, the starter is tested  1004 . The data is logged and the results are displayed  1050 . The results include the condition of the starter and whether the batteries, the magnetic circuit and the cables passed or were repaired.  
         [0106]      FIG. 20  illustrates exemplary processing preformed by the starter test  1004  according to the invention. The starter test  1004  is the final test run when testing the starting system. The test  1004  can also be selected from the main menu as its own test. First, if not previously entered, the unit prompts the operator to enter a vehicle ID number and a technician number in step  750  (according to an embodiment of the invention). If these were previously entered, the testing unit  5  retrieves the information from EEPROM. It is then determined whether the vehicle has a data port  407  by checking EEPROM or by prompting the operator. If the vehicle has a data port  407 , the testing unit  5  instructs the operator to attach the data cable  410  and turn the ignition on (steps  756  and  758 ). At this point, the data cable  410  reads data from the vehicle&#39;s ECU and the unit reads the data from the data cable  410  and displays it (steps  760  and  762 ). After the data is displayed (step  762 ), the operator is instructed to connect the large leads  18   a ,  18   b  to the starter and to connect the small leads  20   a ,  20   b  to the battery (step  764 ). The testing unit  5  verifies that the leads are connected properly (step  766 ). An error message is displayed if it is determined that the leads are not connected properly (step  768 ). After the leads are correctly connected (step  769 ), the unit loads the system and measures the voltage drops in the cables from the battery to the starter while the load current is flowing (step  770 ). In step  772 , the operator is instructed to start the vehicle&#39;s engine. While the engine cranks, the unit measures the voltage at the starter and the voltage drops in the cables (step  774 ). The data is logged and results are displayed (step  776 ).  
         [0107]     The data that may be collected and logged during the starter test includes: beginning voltage, loaded voltage, battery voltage, drop in positive cable under load, cranking voltage, drop in positive cable while cranking, starter current draw, oil temperature (from ECU via the data port), ambient temperature (from ECU via the data port), time, date, vehicle ID, vehicle VIN (from ECU via the data port), and technician number.  
         [0108]     The starter current draw is determined by first determining the resistance of the positive cable. This is accomplished by loading the system at the starter with a load of known resistance. Ohm&#39;s law, I=V/R, gives the current the testing unit  5  pulls through the cable. Where V is the voltage at the testing unit  5  leads and R is the known resistance of the tester load. Next, the resistance of the positive cable is determined, again by using Ohm&#39;s law. Where V is the voltage drop across the positive cable and I is the current that the testing unit  5  pulled through the cable. Once the resistance of the positive cable is known, the current that the starter draw is determined, where V is the voltage drop across the cable while the starter is cranking and R is the resistance of the cable. The test of the starter cables is disclosed in U.S. Pat. No. 6,771,073, which is hereby incorporated by reference herein.  
         [0109]     The colder the oil, the more power it takes to crank the engine. Excessive current draw can indicate a faulty starter. The data collected is used to determine if the current the starter draws exceeds an acceptable amount. The formula for the maximum current is a function of the oil temperature. If the data cable  410  was used, the testing unit  5  reads the engine oil temperature from the ECU. An exemplary formula used to calculate the current draw is: 1400−(oil temperature×4). Where the oil temperature is in degrees Fahrenheit. This formula is only exemplary and will likely be fine tuned as more data is collected.  
         [0110]     At the conclusion of the test, the testing unit  5  reports the beginning voltage, the cranking voltage, the starter draw and if the data cable  410  was used. The testing unit  5  also reports the engine oil temperature and the condition of the starter.  
         [0111]     The data read from the data port  407  and sent to the testing unit  5  via the RS-232 may include the ignition switch position (PID  43 ), pedal position (PID  91 ), battery voltage (PID  168 ), ambient temperature (PID  171 ), oil temperature (PID  175 ), engine speed (PID  190 ), VIN (PID  237 ), clock (PID  251 ), and date (PID  252 ). PID stands for parameter identifier. The PID format and assignments are documented in SAE document J1587.  
         [0112]     The processes and devices described above illustrate exemplary methods and devices of many that could be used to implement the invention. The above description and drawings illustrate exemplary embodiments of the present invention. It should be appreciated that the values used to describe the above identified embodiments are only exemplary. However, it is not intended that the present invention be strictly limited to the above-described and illustrated embodiments and is only limited by the scope of the appended claims.