Abstract:
An automotive battery charging system tester for testing the charging system of an automotive vehicle includes AC and DC voltage measurement circuits and a microprocessor controlled testing sequence. The microprocessor is used to perform a series of tests and to instruct an operator to perform steps associated with performing those tests. Through the application of various loads at various engine speeds, the tester is capable of identifying faults in the battery charging system including a bad battery, problems in the alternator or associated electronics, and problems in the starting system.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to devices for testing an automotive vehicle. More specifically, the present invention relates to a battery charging system tester for an automotive vehicle. 
     Automotive vehicles include a storage battery for operating electronics in the vehicle and using an electric starter to start the vehicle engine. A battery charging system is coupled to the engine and is powered by the engine when the vehicle is running. The charging system is used to charge the storage battery when the vehicle is operating. 
     Many attempts have been made to test the battery of the vehicle. One technique which has been pioneered by Dr. Keith S. Champlin and Midtronics, Inc. of Burr Ridge, Ill. relates to measuring the conductance of batteries to determine their condition. This technique is described in a number of United States patents, for example, U.S. Patent Nos. U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING TO DETERMINE DYNAMIC CONDUCTANCE; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH STATE-OF-CHARGE COMPENSATION; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin, entitled ELECTRONIC TESTER FOR ASSESSING BATTERY/CELL CAPACITY; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994, entitled METHOD AND APPARATUS FOR SUPPRESSING TIME VARYING SIGNALS IN BATTERIES UNDERGOING CHARGING OR DISCHARGING; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996, entitled METHOD AND APPARATUS FOR DETECTION AND CONTROL OF THERMAL RUNAWAY IN A BATTERY UNDER CHARGE; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997, entitled ELECTRONIC BATTERY TESTING DEVICE LOOSE TERMINAL CONNECTION DETECTION VIA A COMPARISON CIRCUIT; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997, entitled ELECTRONIC BATTERY TESTER WITH VERY HIGH NOISE IMMUNITY; U.S. Pat. No. 5,757,192, issued May 26, 1998, entitled METHOD AND APPARATUS FOR DETECTING A BAD CELL IN A STORAGE BATTERY; U.S. Pat. No. 5,821,756, issued Oct. 13, 1998, entitled ELECTRONIC BATTERY TESTER WITH TAILORED COMPENSATION FOR LOW STATE-OF-CHARGE; and U.S. Pat. No. 5,831,435, issued Nov. 3, 1998, entitled BATTERY TESTER FOR JIS STANDARD. 
     With the advent of accurate battery testing, it has become apparent that in some instances the battery in the vehicle may be good, and a problem related to the battery charging system is the cause of the perceived battery failure. A vehicle charging system generally includes the battery, an alternator, a regulator and an alternator drive belt. In most modern vehicles, the regulator is built into the alternator housing and is referred to as an internal regulator. The role of the charging system is two fold. First, the alternator provides charging current for the battery. This charging current ensures that the battery remains charged while the vehicle is being driven and therefore will have sufficient capacity to subsequently start the engine. Second, the alternator provides an output current for all of the vehicle electrical loads. In general, the alternator output, the battery capacity, the starter draw and the vehicle electrical load requirements are matched to each other for optimal performance. In a properly functioning charging system, the alternator will be capable of outputting enough current to drive the vehicle electrical loads while simultaneously charging the battery. Typically, alternators range in size from 60 to 120 amps. 
     A number of charging system testers have been used to evaluate the performance of the vehicle charging system. These testers generally use an inductive “amp clamp.” The amp clamp is placed around a cable or wire and inductively couples to the cable or wire such that the current passing through the wire can be measured. This measurement can be made without having to disconnect the wire. In such a system, typically the operator determines the rated size of the alternator. Next, the operator connects the amp clamp to the output cable of the alternator and an electrical load such as a carbon pile load tester, is placed across the battery. This is a large resistive load capable of receiving several hundred amps which will force the alternator to provide its maximum output. The maximum output current can then be measured using the amp clamp connection. If the measured output is less than the rated output, the alternator is determined to be malfunctioning. Such a test is cumbersome as the equipment is large and difficult to handle. Further, it is difficult, particularly with compact engines, to reach the alternator output cable. Further, in some cases, the amp clamp may not fit around the output cable. It is also very easy to place the amp clamp around the wrong cable causing a false test. 
     Another testing technique is described in U.S. Pat. No. 4,207,611, which issued Jun. 10, 1980 and is entitled APPARATUS AND METHOD FOR CALIBRATED TESTING OF A VEHICLE ELECTRICAL SYSTEM. The device described in this reference monitors voltage changes present at the cigarette lighter of an automotive vehicle in order to determine the condition of the alternator by applying internal loads such as head lamps and blowers, while the engine is running. 
     SUMMARY OF THE INVENTION 
     The present invention includes an automotive battery charging system tester for testing the charging system of an automotive vehicle. The tester includes AC and DC voltage measurement circuits and a microprocessor controlled testing sequence. The microprocessor is used to perform a series of tests and instruct an operator to perform steps associated with those tests. Through the application of various loads at various engine speeds, the tester is capable of identifying faults in the battery charging system including a bad battery, problems in the alternator or associated electronics, and problems in the starting system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified block diagram of an automotive battery charging system tester in accordance with the present invention. 
     FIG. 2 is a simplified flow chart showing steps in a battery test. 
     FIG. 3 is a simplified flow chart showing steps in a starter test. 
     FIG. 4 is a simplified flow chart showing steps in a charging system test. 
     FIG. 5 is a simplified flow chart showing further steps in the charging system test of FIG.  4 . 
     FIG. 6 is a simplified flow chart showing steps in a diesel engine charging system test. 
     FIG. 7 is a simplified flow chart showing steps to remove surface charge. 
     FIG. 8 is a simplified flow chart showing a ripple test. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a simplified block diagram of a battery charging system tester  10  in accordance with one embodiment of the present invention coupled to a vehicle  12 . Vehicle  12  includes a battery  14  having positive and negative terminals, an alternator with internal regulator  16 , various vehicle loads  18 , and a starter motor  20 . In operation, battery  14  provides power to starter  20  and vehicle loads  18  when the engine in vehicle  12  is not running. When the engine in vehicle  12  is running, alternator  16  is used to power vehicle loads  18  and provide a charging current to battery  14  to maintain the charge of battery  14 . 
     Charging system tester  10  includes a microprocessor  30  which controls operation of tester  10  and provides instructions and test result information to an operator through, for example, a display  32 . Tester  10  includes a battery testing section  34  which is illustrated generally as conductance amplifier  36 . Section  34  operates in accordance with, for example, the conductance based battery testing techniques described in Champlin patents U.S. Pat. Nos. U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING TO DETERMINE DYNAMIC CONDUCTANCE; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH STATE-OF-CHARGE COMPENSATION; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin, entitled ELECTRONIC TESTER FOR ASSESSING BATTERY/CELL CAPACITY; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994, entitled METHOD AND APPARATUS FOR SUPPRESSING TIME VARYING SIGNALS IN BATTERIES UNDERGOING CHARGING OR DISCHARGING; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997, entitled ELECTRONIC BATTERY TESTER WITH VERY HIGH NOISE IMMUNITY; U.S. Pat. No. 5,821,756, issued Oct. 13, 1998, entitled ELECTRONIC BATTERY TESTER WITH TAILORED COMPENSATION FOR LOW STATE-OF-CHARGE. Section 34 is illustrated in very simplified form and conductance amplifier  36  provides an output to an analog to digital converter  38  which is related to the internal conductance of battery  14 . 
     A DC voltage sensor  40  includes voltage scaling resistors  42  and  44  and is coupled to battery  14  to provide an output to analog to digital converter  38  which is representative of the DC voltage across battery  14 . Further, an AC ripple detector amplifier  46  is coupled to battery  14  through capacitors  48  and  50  and provides an output to analog to digital converter  38  which is representative of the AC ripple voltage across battery  14 . 
     Microprocessor  30  controls analog to digital converter  38  to select which of the three inputs to digitize. Microprocessor  30  includes firmware, memory, and a software program in accordance with the invention. The user input  54  is coupled to microprocessor  30  to provide the information to microprocessor  30  from an operator. 
     Preferably, tester  10  is portable such that it may be easily moved between vehicles or otherwise transported. Portability of tester  10  is achieved because tester  10  does not require large internal carbon pile loads to load the battery charging system. Instead, as described herein, tester  10  utilizes loads internal to the vehicle  12  in testing the charging system. Further, the battery tester performed by tester  10  is in accordance with the non-load battery testing technique as described above. 
     FIGS. 2-8 are simplified block diagrams illustrating steps in accordance with the invention. User input for the steps can be through user input device  54  and a display can be provided through display device  32 . In FIG. 2, block diagram  100  begins at start block  102 . At block  104  the type of vehicle test is selected. If it is an in-vehicle test, control is passed to block  106 . If it is an out of vehicle test, control is passed to block  120 . At block  106 , the user is prompted to input the battery rating standard to be used for the test. Various standards include SAE, DIN, IEC, EN, JIS or a battery stock number. At block  108 , the user is prompted to input the battery rating according to the selected standard. A battery test is then performed at block  110 , the results of the battery test are displayed including battery voltage, battery cold cranking amps, and a general condition of the battery such as good, good but recharge, charged and retest, replace battery or bad cell-replace. Any type of battery test may be used, however, conductance, resistance, impedance or admittance based testing as described in the Champlin and Midtronics patents is preferred. 
     FIG. 3 is a simplified block diagram  118  for an in-vehicle test. When the user initiates a starter test, for example through an input through user input  54 , control is passed to block  124  and the operator is instructed to start the engine. Microprocessor  30  detects that the engine is being started by monitoring the resultant in drop in voltage across battery  14 . The starting voltage is measured at block  126 . Once the engine starts, and the voltage begins to rise, the tester  10  will display one of four different test results. At block  128 , if the starting voltage is low and the battery is discharged, the message “charge battery” is displayed at block  130 . At block  132 , if the starting voltage is low and the battery has a full charge, the message “cranking voltage low” is displayed at block  134  along with the measured voltage. If at block  136 , the starting voltage is normal and the battery has a full charge, block  138  displays cranking voltage normal along with the measured voltage. If, at block  140 , the battery test result was either replaced or bad cell, block  142  displays the message replace battery. The low and normal cranking voltages can be selected as desired and using known techniques. 
     FIG. 4 is a block diagram  150  which illustrates steps in a charging system test in accordance with another aspect of the invention. At block  152 , the procedure is initiated by the operator while the engine in vehicle  12  is running. At block  154 , the voltage across battery  14  due to alternator  16  is measured and displayed. The operator may press and enter button on user input  54  to continue operation and at block  156  the operator is instructed to turn off all vehicle loads and rev the engine for 5 seconds. At block  158 , the revving of the engine is detected by monitoring the AC ripple across battery  14  using ripple detection amplifier  46 . If, after 30 seconds, microprocessor  30  does not detect engine revving, control is returned to block  156  and the procedure is repeated. At block  160 , the engine revved voltage is measured and control is passed to block  162  where the operator is instructed to turn loads within the vehicle (i.e., headlights, fans, etc.) on and idle the engine. Again, an enter key on user input  54  is pressed and control is passed to block  164  and tester  10  measures the load on, engine idle voltage. At  166 , the user is instructed to rev the engine with the loads on and another voltage is obtained at block  168 . Control is then passed to block  170  in FIG.  5  and it is determined whether the engine speed has increased. At block  172 , if there is no charging voltage, that is i.e., the charging voltage is less than or the same as the idle voltage, an output is displayed. Similarly, if the charging voltage is low such that the total voltage across the battery is less than, for example, 13 volts, an output is displayed. At block  176 , if a high charging voltage is detected, such as more than 2.5 volts above the steady state voltage, an output is displayed. When control reaches block  178 , an output is provided indicative of the diode ripple voltage. This voltage can be obtained during any of the measurements where the engine is revved. If the ripple voltage is greater than, for example, 130 mV, an indication is provided that there is a diode or a stator problem. 
     FIG. 6 is a block diagram of a diesel test algorithm  250 . If the tester  10  does not detect a charging or a ripple voltage, the tester begins the diesel test algorithm shown at  250 . This allows the glow plugs of a diesel engine to turn off. If, at any time during the procedure, a charging voltage and a ripple are detected, the normal test procedure will resume. At block  252 , the user is asked to input information as to whether the engine under test is a diesel engine. If the engine is not a diesel engine, a charging system problem is indicated. If the engine is diesel, control is passed to block  254  and a post heating delay, such as 40 seconds, passes at block  256 , if there is a post heating or glow plugs off condition, then a charging system problem is indicated. If there is a post heating or glow plug on condition, the operator is instructed to warm up the plugs and retest, or check the glow plugs. 
     Additionally, the tester  10  can receive a temperature input from the operator and adjust the battery test appropriately. 
     If the battery test indicates that the battery may have been charged before testing, the user is prompted to indicate whether the test is being performed before charging the battery or after charging the battery and the system is retested. 
     If the tester  10  determines that the battery may have surface charge, the operator is instructed to turn on the vehicle head lights as indicated in flow chart  300  at block  302 . If a drop in voltage is detected at block  304  indicating that the head lights have been turned on, control is passed to block  306 . If, however, the head lights have not been turned on, control is returned to block  302 . At block  306 , the system is retested. Flow chart  320  of FIG. 8 shows a noise detection algorithm. If excessive ripple is detected during engine idle periods at block  322 , the operator is instructed to check system loads at block  324 . At block  326 , the system is retested. 
     Based upon the test, an output can be printed or otherwise provided to an operator indicating the results of the battery test, the battery rating, the actual measured battery capacity, the voltage, the voltage during cranking and whether the cranking voltage is normal, the condition of the charging system along with the idle voltage and the load voltage and the presence of excessive diode ripple. 
     In general, the present invention provides the integration of an alternator test with a battery test, an alternator test with a starter test, a starter test with an battery test, or an alternator test with a battery test and with a starter test. The invention allows information from any of these tests to be shared with the other test(s). 
     In one aspect, tester  10  measures the voltage across battery  14 . Both the AC and DC voltages are recorded. The AC voltage is used to identify alternator diode and stator faults. The DC voltage measurement is used to determine if the charging system is functioning properly. The electrical loads of the vehicle are used to load the alternator for convenience. However, other types of loads can also be applied. The tester continually monitors the charging voltage across the battery. The operator is instructed to turn on vehicle loads and rev the engine. The charging voltage is recorded with the engine revved. In a properly functioning charging system, this charging voltage should be greater than the measured battery voltage with the engine off. This indicates that current is flowing into the battery and thus the battery is being charged even with loads applied to the charging system. This testing principle does not require knowledge of the alternator size, or even the amount of current that the alternator is producing. In the testing, various DC voltages across the battery are measured including battery voltage with the engine off (stead state voltage), battery voltage with the engine running at idle (idle voltage), battery voltage with the engine revved, for example between 1,000 RPM and 2,500 RPM, and the vehicle loads off and battery voltage with the engine revved and vehicle loads on. The AC voltage across the battery which is measured with the engine running is used to detect excessive ripple which may be caused by a faulty diode or stator. Ripple of over about 130 mV is indicative of a diode or stator problem. Additionally, the ripple can be used by tester  10  to detect changes in engine RPM. 
     An initial revving of the engine can be used prior to returning to idle to ensure that the alternator field circuit is excited and conducting current. If the idle voltage with the loads off is less than or equal to the steady state voltage, then a charging problem exists. If the charging voltage exceeds the steady state voltage by more than, for example, 0.5 volts, then a regulator problem is indicated. 
     With the engine revved and the vehicle loads (such as head lights, blower, rear defrost, etc.) turned on, the revved and loaded voltage across the battery is recorded and compared to the steady state battery voltage. If the charging voltage with loads turned on while the engine is revved is not greater than the steady state voltage, then current is not flowing into the battery and the battery is not being charge. This indicates a problem and that the alternator cannot meet the needs of the vehicle while still charging the battery. 
     With the present invention, the battery test can be used to prevent incorrectly identifying the charging system as being faulty. Thus, the battery test ensures that a good battery is being charged during the charging system test. The measurement of the cranking voltage while the engine is being started is used to determine whether there is a starter problem. In diesel engine applications, the charging system voltage is measured to determine if the engine glow plug operation is effecting the charging system test result. A long cabling (i.e., 10 to 15 feet) can be used such that the tester  10  can be operated while sitting in the vehicle. The battery testing is preferably performed by measuring the conductance, impedance, resistance or admittance of the battery. Further, the battery test with the engine off can be compared with the battery test with the engine on and used to diagnosis the system. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.