Electronic battery tester

[0001] The present invention relates to testing of storage batteries. More specifically, the present invention relates to detecting noise in an electronic battery tester while it conducts a battery test.

[0002] Storage batteries, such as lead acid storage batteries of the type used in the automotive industry, have existed for many years. However, understanding the nature of such storage batteries, how such storage batteries operate and how to accurately test such batteries has been an ongoing endeavor and has proved quite difficult. Storage batteries consist of a plurality of individual storage cells electrically connected in series. Typically each cell has a voltage potential of about 2.1 volts. By connecting the cells in series, the voltages of the individual cells are added in a cumulative manner. For example, in a typical automotive storage battery, six storage cells are used to provide a total voltage when the battery is fully charged of 12.6 volts.

[0003] There has been a long history of attempts to accurately test the condition of storage batteries. A simple test is to measure the voltage of the battery. If the voltage is below a certain threshold, the battery is determined to be bad. However, this test is inconvenient because it requires the battery to be charged prior to performing the test. If the battery is discharged, the voltage will be low and a good battery may be incorrectly tested as bad. Furthermore, such a test does not give any indication of how much energy is stored in the battery. Another technique for testing a battery is referred as a load test. In a load test, the battery is discharged using a known load. As the battery is discharged, the voltage across. the battery is monitored and used to determine the condition of the battery. This technique requires that the battery be sufficiently charged in order that it can supply current to the load.

[0004] More recently, a technique has been pioneered by Dr. Keith S. Champlin and Midtronics, Inc. for testing storage batteries by measuring the conductance of the batteries. This technique is described in a number of United States patents, for example, 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. 5,585,416, issued Dec. 10, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; 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. 5,589,757, issued Dec. 31, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; 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. 5,656,920, issued Aug. 12, 1997, entitled METHOD FOR OPTIMIZING THE CHARGING LEAD-ACID BATTERIES AND AN INTERACTIVE CHARGER; 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; U.S. Pat. No. 5,831,435, issued Nov. 3, 1998, entitled BATTERY TESTER FOR JIS STANDARD; U.S. Pat. No. 5,914,605, issued Jun. 22, 1999, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 5,945,829, issued Aug. 31, 1999, entitled MIDPOINT BATTERY MONITORING; U.S. Pat. No. 6,002,238, issued Dec. 14, 1999, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,037,751, issued Mar. 14, 2000, entitled APPARATUS FOR CHARGING BATTERIES; U.S. Pat. No. 6,037,777, issued Mar. 14, 2000, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,051,976, issued Apr. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,081,098, issued Jun. 27, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,091,245, issued Jul. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,104,167, issued Aug. 15, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,137,269, issued Oct. 24, 2000, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,163,156, issued Dec. 19, 2000, entitled ELECTRICAL CONNECTION FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,172,483, issued Jan. 9, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELL AND BATTERIES; U.S. Pat. No. 6,172,505, issued Jan. 9, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,222,369, issued Apr. 24, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,225,808, issued May 1, 2001, entitled TEST COUNTER FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,249,124, issued Jun. 19, 2001, entitled ELECTRONIC BATTERY TESTER WITH INTERNAL BATTERY; U.S. Pat. No. 6,259,254, issued Jul. 10, 2001, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; U.S. Pat. No. 6,262,563, issued Jul. 17, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX ADMITTANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,294,896, issued Sep. 25, 2001; entitled METHOD AND APPARATUS FOR MEASURING COMPLEX SELF-IMMITANCE OF A GENERAL ELECTRICAL ELEMENT; U.S. Patent No. 6,294,897, issued Sep. 25, 2001, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,304,087, issued Oct. 16, 2001, entitled APPARATUS FOR CALIBRATING ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,310,481, issued Oct. 30, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,313,607, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,313,608, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,316,914, issued Nov. 13, 2001, entitled TESTING PARALLEL STRINGS OF STORAGE BATTERIES; U.S. Pat. No. 6,323,650, issued Nov. 27, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,329,793, issued Dec. 11, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,331,762, issued Dec. 18, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Pat. No. 6,332,113, issued Dec. 18, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,351,102, issued Feb. 26, 2002, entitled AUTOMOTIVE BATTERY CHARGING SYSTEM TESTER; U.S. Pat. No. 6,359,441, issued Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,363,303, issued Mar. 26, 2002, entitled ALTERNATOR DIAGNOSTIC SYSTEM, U.S. Ser. No. 09/595,102, filed Jun. 15, 2000, entitled APPARATUS AND METHOD FOR TESTING RECHARGEABLE ENERGY STORAGE BATTERIES; U.S. Ser. No. 09/703,270, filed Oct. 31, 2000, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/575,629, filed May 22, 2000, entitled VEHICLE ELECTRICAL SYSTEM TESTER WITH ENCODED OUTPUT; U.S. Ser. No. 09/780,146,filed Feb. 9, 2001, entitled STORAGE BATTERY WITH INTEGRAL BATTERY TESTER; U.S. Ser. No. 09/816,768, filed Mar. 23, 2001, entitled MODULAR BATTERY TESTER; U.S. Ser. No. 09/756,638, filed Jan. 8, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Ser. No. 09/862,783, filed May 21, 2001, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 09/483,623, filed Jan. 13, 2000, entitled ALTERNATOR TESTER; U.S. Ser. No. 09/870,410, filed May 30, 2001, entitled INTEGRATED CONDUCTANCE AND LOAD TEST BASED ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/960,117, filed Sep. 20, 2001, entitled IN-VEHICLE BATTERY MONITOR; U.S. Ser. No. 09/908,389, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH INTEGRATED CIRCUIT SENSOR; U.S. Ser. No. 09/908,278, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH EMBEDDED ENVIRONMENT SENSOR; U.S. Ser. No. 09/880,473, filed Jun. 13, 2001; entitled BATTERY TEST MODULE; U.S. Ser. No. 09/876,564, filed Jun. 7, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/878,625, filed Jun. 11, 2001, entitled SUPPRESSING INTERFERENCE IN AC MEASUREMENTS OF CELLS, BATTERIES AND OTHER ELECTRICAL ELEMENTS; U.S. Ser. No. 09/902,492, filed Jul. 10, 2001, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; and U.S. Ser. No. 09/940,684, filed Aug. 27, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Ser. No. 09/977,049, filed Oct. 12, 2001, entitled PROGRAMMABLE CURRENT EXCITER FOR MEASURING AC IMMITTANCE OF CELLS AND BATTERIES; U.S. Ser. No. 10/047,923, filed Oct. 23, 2001, entitled AUTOMOTIVE BATTERY CHARGING SYSTEM TESTER, U.S. Ser. No. 10/046,659, filed Oct. 29, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Ser. No. 09/993,468, filed Nov. 14, 2001, entitled KELVIN CONNECTOR FOR A BATTERY POST; U.S. Ser. No. 09/992,350, filed Nov. 26, 2001, entitled ELECTRONIC BATTERY TESTER, U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE; U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE, U.S. Ser. No. 10/073,378, filed Feb. 8, 2002, entitled METHOD AND APPARATUS USING A CIRCUIT MODEL TO EVALUATE CELL/BATTERY PARAMETERS; U.S. Ser. No. 10/093,853, filed Mar. 7, 2002, entitled ELECTRONIC BATTERY TESTER WITH NETWORK COMMUNICATION; U.S. Ser. No. 60/364,656, filed Mar. 14, 2002, entitled ELECTRONIC BATTERY TESTER WITH LOW TEMPERATURE RATING DETERMINATION; U.S. Ser. No. 10/101,543, filed Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/112,114, filed Mar. 28, 2002; U.S. Ser. No. 10/109,734, filed Mar. 28, 2002; U.S. Ser. No. 10/112,105, filed Mar. 28, 2002, entitled CHARGE CONTROL SYSTEM FOR A VEHICLE BATTERY; U.S. Ser. No. 10/112,998, filed Mar. 29, 2002, entitled BATTERY TESTER WITH BATTERY REPLACEMENT OUTPUT; U.S. Ser. No. 10/119,297, filed Apr. 9, 2002, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 10/128,790, filed Apr. 22, 2002, entitled METHOD OF DISTRIBUTING JUMP-START BOOSTER PACKS; U.S. Ser. No. 10/143,307, filed May 10, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/___,___, (C382.12-0112), filed Jul. 29, 2002, entitled KELVIN CLAMP FOR ELECTRICALLY COUPLING TO A BATTERY CONTACT, which are incorporated herein in their entirety.

[0005] However, there is an ongoing need to improve battery testing techniques to increase the accuracy of battery test results. One prior art battery testing technique involves the use of a differential amplifier to measure battery voltage during the application of a time varying current signal to the battery. The presence of noise at the output of the amplifier while the amplifier measures battery voltage during the application of the current signal can introduce errors into test results.

[0006] An electronic battery tester for testing a storage battery is provided. The tester includes a first Kelvin connector that can electrically couple to a first terminal of the battery and a second Kelvin connector that can electrically couple to a second terminal of the battery. Also included, is a source that can apply a time varying forcing function to the battery through a first conductor of the first Kelvin connector and a first conductor of the second Kelvin connector. A sensor that electrically couples to a second conductor of the first Kelvin connector and a second conductor of the second Kelvin connector can sense a response of the storage battery to the applied forcing function and provide a response signal. An analog to digital converter digitizes the response signal. Processing circuitry converts the digitized response signal into multiple Fourier components and determines noise in the response signal from a subset of the multiple Fourier components.

[0007] FIG. 1 is a simplified block diagram of a battery tester in accordance with the present invention.

[0008] FIG. 2 is a graph of voltage and current waveforms generated using a modeling technique.

[0009] FIG. 3 is a graph of a computed Fourier Transform of the current and voltage values of FIG. 2.

[0010] FIG. 4 is a simplified flow chart showing steps in accordance with one embodiment of the present invention.

[0011] FIG. 1 is a simplified block diagram of battery monitoring circuitry 16 in accordance with the present invention. Apparatus 16 is shown coupled to battery 12 which includes a positive battery terminal 22 and a negative battery terminal 24.

[0012] In a preferred embodiment, circuitry 16 operates, with the exceptions and additions as discussed below, in accordance with battery testing methods described in one or more of the United States patents obtained by Dr. Champlin and Midtronics, Inc. and listed above. Circuitry 16 operates in accordance with one embodiment of the present invention and determines the conductance (G_BAT) of battery 12 and the voltage potential (V_BAT) between terminals 22 and 24 of battery 12. Circuitry 16 includes current source 50, differential amplifier 52, analog-to-digital converter 54 and processing circuitry 56. Current source 50 provides one example of a forcing function for use with the invention. Amplifier 52 is capacitively coupled to battery 12 through capacitors C₁ and C₂. Amplifier 52 has an output connected to an input of analog-to-digital converter 54. Processing circuitry 56 can be a microprocessor, digital signal processor, etc. Processing circuitry 56 is connected to system clock 58, memory 60, and analog-to-digital converter 54. Processing circuitry 56 is also capable of receiving an input from input devices 66 and 68. Processing circuitry 56 also connects to output device 72.

[0013] In operation, current source 50 is controlled by processing circuitry 56 and provides a current I in the direction shown by the arrow in FIG. 1. In one embodiment, this is a sine wave, square wave or a pulse. Differential amplifier 52 is connected to terminals 22 and 24 of battery 12 through capacitors C₁ and C₂, respectively, and provides an output related to the voltage potential difference between terminals 22 and 24. In a preferred embodiment, amplifier 52 has a high input impedance. Circuitry 16 includes differential amplifier 70 having inverting and noninverting inputs connected to terminals 24 and 22, respectively. Amplifier 70 is connected to measure the open circuit potential voltage (V_BAT) of battery 12 between terminals 22 and 24 and is one example of a dynamic response sensor used to sense the time varying response of the battery 18 to the applied time varying forcing function. The output of amplifier 70 is provided to analog-to-digital converter 54 such that the voltage across terminals 22 and 24 can be measured by processing circuitry 56.

[0014] Circuitry 16 is connected to battery 12 through a four-point connection technique known as a Kelvin connection. This Kelvin connection allows current I to be injected into battery 12 through a first pair of connections while the voltage V across the terminals 22 and 24 is measured by a second pair of connections. Because very little current flows through amplifier 52, the voltage drop across the inputs to amplifier 52 is substantially identical to the voltage drop across terminals 22 and 24 of battery 12. The output of differential amplifier 52 is converted to a digital format and is provided to processing circuitry 56. Processing circuitry 56 operates at a frequency determined by system clock 58 and in accordance with programming instructions stored in memory 60.

[0015] Processing circuitry 56 determines the conductance of battery 12 by applying a current pulse I using current source 50. This measurement provides a dynamic parameter related to the battery. Of course, any such dynamic parameter can be measured including resistance, admittance, impedance or their combination along with conductance. Further, any type of time varying signal can be used to obtain the dynamic parameter. The signal can be generated using an active forcing function or using a forcing function which provides a switchable load, for example, coupled to the battery 12. The processing circuitry determines the change in battery voltage due to the current pulse I using amplifier 52 and analog-to-digital converter 54. The value of current I generated by current source 50 is known and is stored in memory 60. In one embodiment, current I is obtained by applying a load to battery 12. Processing circuitry 56 calculates the conductance of battery 12 using the following equation: $\begin{array}{cc}{G}_{\mathrm{BAT}}=\frac{I}{V}& \mathrm{Equation}1\end{array}$

[0016] where I is the change in current flowing through battery 12 due to current source 50 and V is the change in battery voltage due to applied current I. Based upon the battery conductance G_BAT and the battery voltage, the battery tester 16 determines the condition of battery 12. Battery tester 16 is programmed with information which can be used with the determined battery conductance and voltage as taught in the above listed patents to Dr. Champlin and Midtronics, Inc.

[0017] The tester can compare the measured CCA (Cold Cranking Amp) with the rated CCA for that particular battery. Processing circuitry 56 can also use information input from input device 66 provided by, for example, an operator. This information may consist of the particular type of battery, location, time, the name of the operator. Additional information relating to the conditions of the battery test can be received by processing circuitry 56 from input device 68. Input device 68 may comprise one or more sensors, for example, or other elements which provide information such as ambient or battery temperature, time, date, humidity, barometric pressure, noise amplitude or characteristics of noise in the battery or in the test result, or any other information or data which may be sensed or otherwise recovered which relates to the conditions of the test how the battery test was performed, or intermediate results obtained in conducting the test. Additional test condition information is provided by processing circuitry 56. Such additional test condition information may include the values of G_BAT and battery voltage, the various inputs provided to battery tester 16 by the operator which may include, for example, type of battery, estimated ambient or battery temperature, type of vehicle (i.e., such as provided through the Vehicle Identification Number (VIN) code for the vehicle) or the particular sequence of steps taken by the operator in conducting the test.

[0018] Typically, prior art battery testers do not take into consideration the presence of noise at the output of amplifier 52 while amplifier 52 measures battery voltage during the application of the current pulse I. However, one aspect of the present invention includes the recognition that the conductance, impedance, resistance or admittance computed as a function of the battery voltage measured using the prior art measurement technique may include a degree of error due to the presence of noise while obtaining the voltage measurement. Noise components that may be present at the output of amplifier 52, while battery voltage measurements are being carried out by amplifier 52, can also be taken into consideration to more accurately determine the condition of battery 12. Thus, processing circuitry 56 utilizes different components corresponding to different frequencies of voltage measured by amplifier 52 to determine condition information of battery 12.

[0019] In accordance with the present invention, the digitized response signal, corresponding to the battery voltage measured by amplifier 52, obtained at the output of analog-to-digital converter 54, is converted into a plurality of Fourier components by processing circuitry 56. Processing circuitry 56 also determines noise in the response signal from a subset (less than all) of the plurality of Fourier components. The condition of battery 12 is then output by processing circuitry 56 if the noise in the response signal is below a predetermined threshold. As used herein, Fourier components are values obtained as a result of applying a Fourier Transform to a current or voltage signal. The Fourier components provide a frequency domain representation of the current or voltage signal.

[0020] In a narrower aspect of the present invention, a first battery capacity measurement (peak-to-peak battery capacity measurement) is obtained as a function of the peak-to-peak battery voltage measured by amplifier 52 during the application of current pulse I to battery 12, and a second battery capacity measurement (DFT battery capacity measurement) is obtained as a function of the Fourier components of the battery voltage measured by amplifier 52 during the application of current pulse I to battery 12. The current or actual battery capacity is then determined as a function of the first battery capacity measurement and the second battery capacity measurement. In some embodiments of the present invention, if the difference between the first battery capacity measurement and the second battery capacity measurement is within a predetermined threshold, the first battery capacity measurement is output as the actual battery capacity. If the difference between the first battery capacity measurement and the second battery capacity measurement is greater than or equal to the predetermined threshold, the first battery capacity measurement is discarded, and a message is output notifying the tester user of the presence of noise in the battery testing system. Tester 16 can then automatically retest battery 12 after a brief waiting period (for example, 3-4 seconds). Tester 16 carries out the retest by reapplying the current pulse, carrying out a new voltage measurement, recalculating the first and second capacity measurements and comparing these measurements. The tests are repeated until the difference between the first battery capacity measurement and the second battery capacity measurement is below the preset threshold. In some embodiments of the present invention, the output can include a measured noise energy value. An algorithm for determining the peak-to-peak battery voltage measurement, the Fourier components of the measured voltage, and the noise energy can be derived experimentally or through modeling techniques. One such algorithm is described below in connection with FIGS. 2 and 3.

[0021] FIG. 2 shows current and voltage waveforms from which first and second battery capacity measurements can be obtained. These waveforms are generated as

[0022] and

[0023] where IDiff_i and VDiff_i are the respective values of current and voltage computed for a particular sample index i (i0 . . . n1, where n is the number of samples), IMag and VMag are the respective current and voltage magnitudes, IMax and VMax are the respective maximum current and voltage values, IMin and VMin are the respective minimum current and voltage values and p and q are integers that determine the frequency at which maximum and minimum voltage and current values occur.

[0024] In FIG. 2, IDiff_i and VDiff_i are plotted along the vertical axis as functions of index i plotted along the horizontal axis to produce voltage waveform 80 and current waveform 82. To generate these example current and voltage waveforms shown in FIG. 2 the following values were used in Equations 1 and 2:

[0025] n384

[0026] IMag100

[0027] IMin0

[0028] IMax1

[0029] VMag1500

[0030] VMax0

[0031] VMin1

[0032] The peak-to-peak magnitude of current (IDiffPP) and the peak-to-peak magnitude of voltage (VDiffPP) for current and voltage signals generated utilizing equations 1 and 2 are computed as

[0033] and

[0034] IDiffPP and VDiffPP values determined using Equations 3 and 4 are employed to determine peak-to-peak battery capacity as described further below in connection with Equation 11.

[0035] FIG. 3 shows a Discrete Fourier Transform (DFT) current magnitude response and a DFT voltage magnitude response for the respective current and voltage waveforms shown in FIG. 2. In general, the DFT current and voltage magnitude responses are generated as

[0036] where x(m) is input series IDiff_m (current) or VDiff_m (voltage) in time and x(k) is the output current or voltage series in frequency calculated for an input sample index m (m0 . . . N1, where N is the number of samples) and an output sample index k $\left(k=0\frac{N}{2}-1\right).$

[0037] In one embodiment of the present invention, to compute the DFT current magnitude response and the DFT voltage magnitude response, the direct current (DC) or zero Hz frequency component of the current magnitude response (IDiffMag₀) and the DC component of the voltage magnitude response (VDiffMag₀) are first set to zero.

[0038] and

[0039] The remaining components of the DFT current magnitude response (IDiffMag_k1) and the DFT voltage magnitude response (VDiffMag_k1) are then computed as

[0040] and

[0041] In FIG. 3, IDiffMag_k1 and VDiffMag_k1 are plotted along the vertical axis as functions of index k along the horizontal axis to produce current magnitude response plot 90 and voltage magnitude response plot 92. To generate the example current and voltage magnitude response plots shown in FIG. 3 the following values were used in Equations 5:

[0042] N256

[0043] m0 . . . 255

[0044] k0 . . . 127

[0045] The battery capacity is separately determined from peak-to-peak current and voltage values and DFT magnitude values as $\begin{array}{cc}\mathrm{CapacityPP}=\frac{K\mathrm{IDiffPP}}{\mathrm{VDiffPP}}\mathrm{and}& \mathrm{Equation}11\\ \mathrm{CapacityDFT}=\frac{K{\mathrm{IDiffMag}}_F}{{\mathrm{VDiffMag}}_F}& \mathrm{Equation}12\end{array}$

[0046] where CapacityPP is the peak-to-peak battery capacity expressed in cold cranking amps (CCA), CapacityDFT is the capacity calculated from the DFT magnitude response also expressed in CCA, K is a constant having units of (CCA*Volts)/Amperes, IDiffMag_F is the DFT current magnitude response value at the fundamental frequency (frequency at which the current pulse is applied to the battery) and VDiffMag_F is the DFT voltage magnitude response value at the fundamental frequency.

[0047] In the example DFT magnitude response shown in FIG. 3, IDiffMag_F and VDiffMag_F values are at k43 for a fundamental frequency F100 Hz.

[0048] A determination is made that system noise is present if the absolute value of the error between peak-to-peak capacity and the DFT capacity is greater than a predetermined threshold percentage. This capacity error is computed as $\begin{array}{cc}\mathrm{CapacityError}=\frac{\mathrm{CapacityPP}-\mathrm{CapacityDFT}}{100\mathrm{CapacityPP}}& \mathrm{Equation}13\end{array}$

[0049] Also, if the sum of the noise energy of VDiffMag_k is above a Floor level and is more than a predetermined percentage of the fundamental frequency component a determination is made that system noise is present. The noise energy is computed as $\begin{array}{cc}\mathrm{NoiseEnergy}=\frac{\begin{array}{c}\underset{k=0}{\overset{\frac{N}{2}-1}{}}\mathrm{if}\left({\mathrm{VDiffMag}}_k>\mathrm{Floor},{\mathrm{VDiffMag}}_k,0\right)\\ {\mathrm{VDiffMag}}_F-{\mathrm{VDiffMag}}_{F-1}-{\mathrm{VDiffMag}}_{F+1}\end{array}}{100{\mathrm{VDiffMag}}_F}& \mathrm{Equation}14\end{array}$

[0050] where VDiffMag_F1 is the DFT voltage magnitude response value immediately previous to VDiffMag_F, and VDiffMag_F1 is the DFT voltage magnitude response value immediately after VDiffMag_F.

[0051] In the example DFT magnitude response shown in FIG. 3, IDiffMag_F and VDiffMag_F values are at k43, VDiffMag_f1 is at k42, VDiffMag_F1 is at k44 and the Floor magnitude is equal to 400. The Floor magnitude is represented by reference numeral 94 in FIG. 3.

[0052] FIG. 4 is a simplified flow chart 100 showing steps in accordance with one aspect of the present invention. Step 102, a time varying forcing function is applied to the battery through a first pair of connectors of a Kelvin connection. At step 104, the response of the battery to the applied time varying forcing function is sensed through a second pair of connectors of the Kelvin connection to provide a response signal. At step 106, the response signal is digitized. At step 108, the digitized response signal is converted into multiple Fourier components. At step 110, an output related to a condition of the battery is provided as a function at least one of the multiple Fourier components.

[0053] The present invention may be implemented using any appropriate technique. For simplicity, a single technique has been illustrated herein. However, other techniques may be used including implementation in all analog circuitry.

[0054] 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. A Fast Fourier Transform (FFT) algorithm may be utilized instead of the DFT algorithm to determine the Fourier components described above. The forcing function can be formed by a resistance, by a current sink, through an existing load of the vehicle or any other suitable means. The dynamic parameter determined for the battery may be real or imaginary.