Storage Battery Electrolyte Temperature Measuring Apparatus

This invention relates to apparatus for measuring the electrolyte temperature in a storage battery and more particularly relates to such apparatus particularly useful where physical access to the battery electrolyte is either not possible or not convenient without destruction of all or a portion of the battery and further contemplates the provision of automatic battery analyzing apparatus including such temperature measuring apparatus.

There has in the past been much effort at developing apparatus for determining the condition of storage batteries such as the lead-acid type normally used for starting, lighting, and ignition in the automotive field and, in particular, for determining the acceptability of such batteries for use under adverse conditions such as the starting of an automobile engine at low temperatures. It has been known in the past that in making such a determination the temperature of the battery at the time any tests are being made thereon must be taken into account since the performance of a lead-acid storage battery varies widely with variations in temperature. The advent of automotive batteries with either no means for access to the battery electrolyte or with such means suitable for only infrequent use has created a need for apparatus for determining the acceptability of a battery which apparatus does not require any access to the interior of the battery or any physical contact with the battery electrolyte and which is also capable of compensating for the temperature of the battery under test. The testing of automotive batteries is further complicated by the conditions under which they are commonly tested. Since the performance of automotive batteries is most critical during cold weather, such batteries are most often tested during cold weather when, for example, the battery itself may be at a very low temperature, often many degrees below freezing, because it has been outside for a prolonged period of time. However, the actual testing of the battery may be performed in a relatively warm environment when a battery already in service is removed from the automobile and taken inside for testing or the automobile is driven into a service bay. In such instances, the battery electrolyte normally will be at approximately the ambient outside temperature, but the portions of the battery conveniently accessable for measuring temperature, such as the battery connector or post, will not be at the battery electrolyte temperature but rather at some temperatures intermediate the electrolyte temperature and the ambient inside temperature. It is important that the battery temperature be determined sufficiently accurately that the results of the battery test are not adversely effected; it is particularly important that the temperature be determined accurately in the low temperature range because of the relative ineffeciency of battery operation at low temperatures and the sensitivity of battery efficiency to relatively small temperature changes.

Apparatus for automatically analyzing the condition of an automotive battery including circuitry attempting to account for the battery temperature are known in the prior art. Such apparatus and various of the desideratum of such apparatus are disclosed in the U.S. patent application of C. E. Frailing and T. J. Dougherty, Ser. No. 863,925, filed Dec. 23, 1977 now Pat. No. 4,193,025, entitled "Automotive Battery Analyzer" and assigned to the assignee of this application, now U.S. Pat. No. 4,193,025 which issued on Mar. 11, 1980. The disclosure of that application is hereby incorporated by reference. The apparatus shown therein took temperature measurements of the battery's negative terminal or post at two times, the time at which the leads of the apparatus were connected to the battery terminals and the time five seconds later. On the basis of empirical observation, it was estimated that the difference between the two measured temperatures was approximately one-fourth of the difference between the initial measured temperature and the actual battery temperature, and this approximation was used to calculate an estimated battery temperature. However, further work with automatic battery analyzers has shown that increased accuracy over that provided by the prior approach is desirable.

In the design of temperature measuring apparatus for use with automotive battery analyzers, a number of criteria must also be considered in addition to the accuracy of the resultant measurement. It is necessary that the apparatus not be so complex that relatively unskilled personnel would have difficulty in using it. It is desirable that the apparatus be useful with a wide variety of different types of battery designs. Specifically, it is desirable that the apparatus be useful with batteries of the traditional type having the connector posts located on the top surface of the battery as well as with batteries of the more recently introduced type having posts located on a side surface of the battery. It is necessary that the apparatus be useful when the battery is either in an automobile in its normal service location or removed from the automobile. It is also desirable that the apparatus be of such a physical construction that it can be used in a wide variety of automobiles which, for example, may have battery covers, battery shields or cases, structural members of the automobile, or other components of the automobile located in different physical relationships to, and closely adjacent, the battery. Finally, it is necessary that the temperature measuring apparatus not be such that either the temperature measurement itself or the period required for the associated battery analyzer circuit to test a battery be undersirably long.

Thus, it is an object of this invention to provide apparatus for measuring the temperature of a storage battery which is particularly useful for use with battery analyzing apparatus and which has greater accuracy than such apparatus heretofore available.

It is an object of this invention to provide apparatus for measuring the temperature of the electrolyte of a storage battery without physical contact with the electrolyte and without otherwise penetrating into the interior of the battery.

It is an object of this invention to provide apparatus for accurately measuring the electrolyte temperature of a storage battery which may easily be used by relatively unskilled persons.

It is an object of this invention to provide apparatus for accurately measuring the electrolyte temperature of automobile storage batteries which may be used with a large variety of different types of batteries.

It is an object of this invention to provide apparatus for accurately measuring the electrolyte temperature of automobile storage batteries useful with batteries located in a wide variety of types and designs of automobiles.

It is an object of this invention to provide apparatus for accurately measuring the electrolyte temperature of automobile storage batteries for use with associated battery analyzing apparatus and being such that neither the time required to make the temperature measurement nor the time required to analyze the battery is excessively long.

It is an object of the invention to provide automatic battery temperature measuring apparatus which meet the aforementioned objects and are further characterized by simplicity of design, ease of operation, and economy of construction.

Further and additional objects of this invention will be apparent from this description, the drawing, and the appended claims.

FIG. 1 is a diagramatic view of the interior of a lead-acid storage battery useful for explaining the operation of the preferred embodiment of this invention;

FIG. 2 is a graph useful for explaining the operation of the preferred embodiment of this invention;

FIG. 3 is a diagram partly in block form and partly in a schematic form of an automatic battery analyzer including the preferred embodiment of this invention;

FIG. 4 is a schematic diagram of the temperature sensing circuit of the apparatus of FIG. 3;

FIG. 5 is a schematic diagram of the load shank of the apparatus of FIG. 3;

FIGS. 6a-6c show the brass connector of the apparatus of FIG. 3 for connection to the negative terminal of the battery under test; and

FIGS. 7a-7e are a flow diagram of the apparatus of FIG. 3.

FIG. 1 is a diagramatic view for use in explaining the operation of an embodiment of this invention and shows in schematic form a cross section of a multicell storage battery 10 of the lead-acid type normally used for starting, lighting, and ignition in automotive applications. Each cell includes two electrodes and is filled with electrolyte, one electrode from each of the two end cells extending through the battery case to form a post or terminal; the intercell connections are omitted from FIG. 1. A brass connector 12 is provided by the apparatus of this invention and is placed over the end of and in thermal contact with the negative battery post 14. For the purposes of thermal analysis, the system including the connector 12 situated in the ambient air, the battery post 14 and the electrode to which it is attached extending and the electrolyte 16 within that cell may be isolated for consideration. The mass and thermal capacity of the electrolyte are sufficiently large and the electrolyte is sufficiently insulated from the effects of the ambient air by the battery case that the electrolyte temperature may be considered to be essentially constant at least over relatively short time periods such as a few minutes. The temperature of the battery electrolyte at the surface of the battery electrodes heavily influences the rate of the chemical reactions that occur in the battery and, thus, the battery performance. It is common in the testing of automobile storage batteries that the battery is brought from a relatively cold outside environment to a relatively warm inside environment to test the condition of the battery and the apparatus used to perform the test is already at the inside ambient temperature. In such situations when the relatively warm connector 12 is placed upon and in thermal contact with the negative battery post, there is a relatively rapid heat flow from the connector to the negative battery post lowering the temperature of the connector and raising the temperature of the post. The result is that the temperature of the connector falls from the inside ambient temperature in a manner such as is shown in FIG. 2 wherein the relative values of the electrolyte, connector and ambient temperatures are shown as a function of the time following attachment of the connector to the negative battery post. The variation in the connector temperature may be represented as follows:

where

T.sub.B (t) =the connector temperature

T.sub.A =the ambient temperature

T.sub.E =the electrolyte temperature

t=the time following attachment of the connector to the battery post

.tau.=the thermal time constant of the connector

K.sub.1 and K.sub.2 are constants and may be evaluated empirically from measured data. The thermal time constant of the connector, .tau., is related to the physical properties of the connector and is equal to the product of thermal resistance of the connector times its thermal capacitance. Thus:

where

R=the thermal resistance of the connector

C=the thermal capacitance of the connector

The thermal resistance and thermal capacitance of the brass connector are further defined as follows:

R=b/KA

b=the thickness of the connector in feet

A=the surface area of the connector exposed to the ambient air in square feet

K=the thermal conductivity of the connector in B.T.U. per hour--square foot--Fahrenheit degree

C=MS

M=the mass of the connector in pounds

S=the specific heat of the connector in B.T.U. per pound--Fahrenheit degree

If the time period t is permitted to become sufficiently large, the value of the exponential terms in the equation above for T.sub.B (t) become sufficiently small that they may be neglected, so that the equation becomes:

The electrolyte temperature may then be calculated as follows:

There is disclosed in the remaining figures of the drawing apparatus for measuring the electrolyte temperature of a lead-acid, automotive, starting, lighting a and ignition battery making use of the above relationship. FIG. 3 is a block diagram of an automatic battery analyzer apparatus incorporating this invention and FIGS. 4 and 5 are schematic diagrams of particular circuits of the apparatus of FIG. 3. The apparatus of FIGS. 3-5 as actually constructed included provisions for analyzing portions of an automobile other than the battery. As those other provisions form no part of the present invention, they are not included in the following description to the extent feasible to avoid obscuring the present invention.

The automatic battery analyzer disclosed in FIG. 3 includes a microprocessor controller circuit 100, first, second, and third peripheral interface adapters (PIA's) 102, 104, and 106, respectively, for interfacing various input and output circuits to the microprocessor 100, and two programmable read only member circuits 108 and 110 for storage of the program used to control the operation of the microprocessor 100. The microprocessor 100 is an MC6802 and each of the PIA's is an MC6821 available from Motorola Semiconductor Products Inc., Austin, Texas; extensive information concerning the interconnections, use, and programming of these devices is available from Motorola Semiconductor Products Inc. Equivalent devices manufactured by others could be used and corresponding information concerning such devices is available from their respective manufacturers. The memories 108 and 110 are known by the industry standard designation 2716 and are each 8 bits by 2048 words; they are commercially available from a number of different manufacturers. Only the interconnections of the address bus (a sixteen line bus indicated as A0-A15 in FIG. 4), the data bus (an eight line bus indicated as D0-D7), and the reset line between the microprocessor, the PIA's, and the memories are indicated in FIG. 3 as the remainder of the necessary interconnections will be apparent to those familiar with the published information concerning these devices. Further detail is unnecessary and would unnecessarily complicate this description and perhaps obscure the invention. Simlarly, only the connections between the PIA input/output data lines and control lines and the various input and output devices are shown in FIG. 3.

Each of the PIA's 102, 104, and 106 includes A and B side eight bit, input/output data registers (PA0-PA7 and PB0-PB7), and A and B side two bit control registers (CA1, CA2, CB1, and CB2). Address lines A0 and A1 are connected to register select inputs of each of the three PIA's 102, 104, and 106, and a PIA select circuit 112 has inputs coupled to address lines A2, A3, A7, and A15 and outputs coupled to device select inputs of the three PIA's 102, 104, and 106 such that decoding of the address lines occurs placing the PIA registers at the addresses shown in Table 1 hereinafter. Address lines A0-A10 are connected to address inputs of the memories 108 and 110 and a memory select circuit 114 has inputs coupled to address lines A13, A14, and A15 and outputs coupled to device select inputs of memories 108 and 110 such that decoding of the address lines occurs placing the memories at hexadecimal addresses FOOO-FFFF.

The input information to the automatic battery analyzer of FIG. 3 is supplied through the first PIA 102. The battery under test 114 has its negative terminal coupled through connector 12 and through a low resistance current shunt 116 to one terminal of a variable resistance load bank 118. The positive terminal of battery 114 is coupled to a second terminal of load bank 118. The variable resistance load bank 118 is connected to an operated by a set of load bank relays 120 and is effective to place a variable resistance load across the battery under test. The magnitude of that load is determined by which one or ones of the load bank relays 120 are closed. A differential amplifier circuit 122 is provided having its inputs coupled across the battery under test 114 and its output coupled to one signal input of an analog switch 124. A differential amplifier circuit 126 has its inputs coupled across the current shunt 116 and has its output coupled to another signal input of analog switch 124. The signals at the outputs of amplifier circuits 122 and 126 are responsive to the voltage across and the current through the battery under test, respectively, at any instant of time. A temperature sensing circuit 128 includes a thermocouple 130 physicially located in the connector 12 coupled to the negative terminal of the battery under test; the circuit 128 will also be described in further detail hereinafter. An output of circuit 128 is responsive to the temperature of thermocouple 130 and is coupled to a third signal input of analog switch 124. The series connection of two variable resistances 132 and 134 and a potentiometer 138 is connected between a positive supply source +V and circuit ground with the tap on potentiometer 136 being coupled to a fourth signal input of analog switch 124. Potentiometer 136 is calibrated so that the user may adjust it to a position corresponding to the cold cranking rating of the battery under test whereas variable resistors 132 and 134 are used for calibration. The analog switch 124 is effective to develop at an output a signal responsive to that present at a selected one of its signal inputs and has input select inputs coupled to data lines PA0-PA2 of the A side of the third PIA 106. The output of analog switch 124 is coupled to the input of a three and one-half digit analog-to-digital converter 138. The data lines PB4-PB7 of the first PIA 102 are coupled to the digit select lines of analog-to-digital converter 138, the outputs of analog-to-digital converter 138 are coupled to the data lines PB0-PB3 of the first PIA 102, and the data update terminal and the end of conversion terminal of the analog-to-digital converter 138 are coupled to the control line CB2 and CB1, respectively, of the first PIA 102. A voltage reference source 139 is also coupled to the analog-to-digital converter 138. Thus, signals representing separate digits of the battery current and voltage and connector temperature are applied to the microprocessor data bus by the first PIA 102 in response to the generation of proper signals by the first and third PIA's 102 and 106. Analog switch 124 and analog-to-digital converter 138 may comprise, respectively, MC14051 and MC14433 units available from Motorola Semiconductor Products, Inc. with appropriate associated circuitry.

A power up and reset circuit 140 is provided for resetting the microprocessor 100 and PIA's 102, 104, and 106 when power is initially applied to the battery analyzer. The circuit has an output providing a signal to the reset inputs of the microprocessor 100 and each of the PIA's 102, 104, and 106 of proper magnitude and duration to cause resetting of these units to their initial condition. A "Stop" switch 142 is coupled to the circuit 140 for manual actuation so that an operator may stop a test in progress by closing the switch and resetting the microprocessor and the PIA's. Two manually operated switches 144 and 146 labelled "Test" and "Retest" are coupled to a switch encoder circuit 148. Manual operation of these switches indicates either that the operator desires to perform an initial test on the battery or that he wishes to retest a battery previously tested for reasons which will be discussed subsequently. Encoder circuit 148 is effective to apply an appropriate code to data lines PA0-PA3 of first PIA 102 in response to the status of switches 144 and 146.

Three forms of output devices are driven by the second and third PIA's 104 and 106, the variable resistance load bank 118 previously described, a light emitting diode display matrix 160, and a three-and-one-half digit display 162. The data lines PA0-PA7 and control line CB2 of the second PIA 104 are each individually coupled through one of a set of optically coupled isolators and drivers 164 to a relay in a set of load bank relays 120 such that the signals on those lines are each operative to control the operation of one of the relays. The relays controlled by data lines PA0-PA6 determine the magnitude of a variable resistance load placed across the battery under test with each controlling the current flow through one of a set of seven resistances connected in parallel. A schematic drawing of the load bank 118 with the associated relay contacts of the load bank relays 120 as well as the shunt 116 is shown in FIG. 5. The positive terminal of the battery under test is coupled to one contact of each of eight normally open pairs of contacts 300, 302, 304, 306, 308, 310, 312, and 314. The other contacts of each of those pairs is connected to one terminal of a resistor 318, 320, 322, 324, 326, 328, 330, and 332, respectively, the other terminal of those resistors being connected together to the shunt 116. The relative magnitudes of the six resistors 318-328 are in binary increments with resistor 328 having the least resistance, and the magnitudes of the three resistors 328-332 are equal. A relay coil 334 is coupled across resistor 330 and operates a normally open contact pair 336 coupled in parallel with the contact pair 314. The relays 300-312 are operated in response to the signals on data lines PA0-PA6 of the second PIA 104, respectively, whereas relay 314 is operated in response to the signal on control line CB2 of that same PIA. Relays 300-312 and their associated resistors are effective to place a variable resistance load across the battery under test, but relay 314 is effective to place a fixed resistance load across the battery.

The light emitting diode matrix 160 includes 8 separate series combinations of a resistor and a light emitting diode, the light emitting diodes 170, 172, 174, 176, 178, 180, 182, and 184 being labelled to indicate "Testing" or test in progress, "Recharge/Retest", "Good/Recharge", "Bad", "Good", "Load Test On", "Low Voltage", and "Polarity Reversed", respectively. Control lines CA2 and CB2 of the third PIA 106 are coupled to a decoder/driver circuit 186 to enable one of the vertical matrix lines of the matrix 160, only one such vertical matrix line actually being shown in the apparatus of FIG. 3. Data lines PB0-PB7 of the third PIA 106 are individually coupled through one of a set of drivers 188 to the light emitting diode/resistor series combinations of the matrix 160 in order to appropriately select a particular one of the diodes for energization.

The digit display 162 would normally not be used with the battery analyzer of FIG. 3, but may be used when it is desired to know the value of the voltage appearing at the output of the analog switch 124 at any particular time. A manually operated switch, not shown, is coupled to data line PA3 of the third PIA 106 for coupling that line to circuit ground when no such display is desired and to a positive potential when such a display is desired. The data lines PB0-PB7 are individually coupled through one of a set of drivers 190 of PIA 106 to the segment and decimal point select lines of the display 162 and the data lines PA4-PA7 are individually coupled through one of a set of drivers 192 to the digit select lines of the display 162.

FIG. 4 is a detailed schematic diagram of the temperature sensing circuit 128 used to develop a signal responsive to the temperature of thermocouple 130. The thermocouple 130 is comprised of a copper/constantan junction. The copper side of that junction is coupled through copper lines 200, 202, and 203, and through a resistor 204 to the inverting input of a differential amplifier 206. The constantan side of that junction is coupled through constantan lines 208 and 209 to another copper/constantan junction 210 and then through copper lines 212 and 214 and through a resistor 216 to the noninverting input of amplifier 206, that input also being coupled to ground through a resistor 218. Feedback is provided through a resistor 220 coupled from the output of differential amplifier 206 to its inverting input. Differential amplifier 206 is coupled to positive and negative supply voltages +V1 and -V1, respectively, and a capacitor 222 is coupled from the positive power supply for the differential amplifier to the frequency compensation input thereof. The output of differential amplifier 206 is coupled through a resistor 224 to the inverting input of another differential amplifier 226.

A temperature compensating network 228 is also coupled to the inverting input of differential amplifier 226. Network 228 includes a temperature transducer 230 having its power supply terminals coupled to circuit ground and through a resistor 232 to the negative supply voltage -V1. The output of the transducer is coupled through a resistor 234 to the inverting input of differential amplifier 226. The copper/constantan junction 210 is placed in physical contact with the temperature transducer 230 so that the transducer is responsive to the temperature of that junction. A reference diode with built-in heat source 236 (e.g., an LM 399Z) is included having its anode coupled to circuit ground, its supply input for the heat source coupled to the positive voltage supply +V1, and its cathode coupled to the positive supply +V1 through a resistor 238 and to the inverting input of amplifier 226 through the series combination of a variable resistor 240 and a fixed resistor 242.

The output of differential amplifier 226 is coupled both to the inverting input thereof through the series combination of two resistors 244 and 246 to provide feedback and to an output terminal point 248 through a resistor 250. The output terminal point 248 is coupled to one input of the analog switch 124. A protection circuit 252 is also coupled to output circuit point 248 to limit the magnitude of the potential at that circuit point and protect the input to analog switch 124 from excess potential. That network includes first and second diodes 254 and 256 having their cathode and anode terminals, respectively coupled to output circuit point 248 and their other terminals coupled to circuit points 258 and 260, respectively. Those latter two circuit points are each coupled to ground through resistor 262 and 264 with circuit point 258 being also coupled to the anode of a diode 266 having its cathode coupled to a second negative voltage supply -V2 of greater voltage (i.e., less negative) than the first negative voltage supply -V1 and circuit point 260 also being coupled to the cathode of a diode 268 having its anode coupled to a second positive voltage supply +V2 of lesser voltage than the first positive voltage supply +V1. The temperature sensing circuit 128 provides an output of approximately 20 millivolts per .degree.F. The solid state temperature transducer 230 compensates for changes in temperature of the reference junction 210. The reference diode 236 and associated resistors provide a constant, temperature stable, offset voltage.

The thermocouple 130 is physically located within a connector 400 attached to the negative post of the battery under test. The connector 400 is disclosed in FIGS. 6a-6c. The connector includes a connector block 402 having a circular portion 403 and a shank portion 405. A receptacle opening 404 on one side of circular portion 403 extends partway through the connector block for receiving the negative post or terminal of the battery under test. Receptacle opening 404 may be tapered so that the connector block 402 may easily be fit snugly onto the negative post of the battery under test. A thumbscrew 406 is provided which screws into a threaded opening 408 in the connector block 402. Opening 408 is disposed so that as thumbscrew 406 is advanced into it, a portion of the thumbscrew extends into the receptacle opening 404 so as to firmly attach the connector 402 to the battery negative post. An opening 410 is provided in circular portion 403 on the other side of receptacle opening 404 and extending through the connector block into communication with the receptacle opening. When the battery analyzing apparatus is connected to a battery having a threaded opening in the top of the negative post, such as are typical on side post automotive batteries, the thumbscrew 406 may be placed through opening 410 and advanced into the threaded opening on the battery post to secure the connector block 402 to the battery post.

The connector block shank portion 403 additionally has three openings 412, 414, and 416 at the base thereof and extending lengthwise through it. Opening 412 is sufficiently large to receive the electrical conductor which is coupled to the current shunt 16, whereas opening 414 need only be sufficiently large to receive the conductor coupled to the inputs of amplifier circuits 122 and 126. Opening 416 is of sufficient diameter to receive thermocouple 130 and its connecting wires 200 and 208 and retain the thermocouple 130 in thermal contact with the connector block 402. Opening 416 extends through the shank portion 405 into the circular portion 403 to permit the thermocouple 130 to be in thermal contact with the connector block 402 at a position relatively close to the receptacle opening 404. Threaded openings 418, 420, and 422 are provided in the connector block 404 and each is in communication with one of openings 412, 414, and 416, respectively, for receiving set screws to retain the associated conductors in the openings 412, 414, and 416. In an apparatus constructed in accord with this invention, the connector block had an overall length of 2.50 inches, a width of 1.00 inches, and the circular portion 403 and the shank portion 405 had thicknesses of 0.79 and 0.70 inches, respectively. In that apparatus, the time constant t of the connector block was approximately 30 seconds and thus was in the presently preferred range of approximately 25 to 35 seconds.

A flow chart disclosing the operation of the automatic battery analyzer of FIGS. 3-6 is shown in FIGS. 7a-7e, the presence of the same reference letters on different lines of those FIGS. 7a-7e indicating that those lines are connected together. As soon as the automatic battery analyzer is turned on by applying power thereto, a loop 500 is entered which successively measures and stores the temperature of the connector block 402, scans the pushbutton switches 144 and 146 to see if either one has been closed, and measures the potential across the battery connectors. As long as the voltage across the battery connectors is within the range of plus or minus 2.0 volts, it is assumed that the battery analyzer has not yet been connected to the battery under test and that the measured temperature of the connector block, T.sub.A, is the ambient temperature. When the measured voltage across the battery connector is outside the plus or minus 2.0 volt range, a second loop 502 is entered which skips the temperature measurement and storage steps of loop 500 since the connector block is no longer at ambient temperature but is at some temperature between the ambient temperature and the battery post temperature. Thus, after the connector is attached to the battery under test, the stored value of T.sub.A is temperature of the connector measured at the most recent time prior to connection of the connector to the battery.

When either of switches 144 or 146 is closed, a lamp test procedure 504 is performed by which all of the light emitting diodes 170-184 are simultaneously illuminated for a period of five seconds so that the operator may verify that each of them is functional. Another loop 506 is then entered which reads the battery voltage and, if that voltage is negative, turns on the light emitting diode 184 indicating to the operator that he has incorrectly connected the battery analyzer to the tester and that the positive and negative connectors should be reversed. If this occurs, the analyzer returns to the loop 500 when it is disconnected from the battery under test. After loop 506, the light emitting diode 170 is turned on to indicate that a test is in progress, the appropriate registers are set to zero, and the battery voltage is again read. If the battery voltage is less than 10.8 volts (for a nominal 12 volt battery) at the commencement of the test with no load applied to it, the battery is assumed to be unacceptable, light emitting diode 176 is turned on indicating that the battery under test is unacceptable, light emitting diode 182 is turned on indicating that the battery terminal voltage is excessively low, light emitting diode 170 is turned off indicating the test has terminated, and the analyzer returned to loop 502 and, after the bad battery is disconnected from the analyzer, to loop 500, in readiness for the next test.

If the battery voltage at the beginning of the test is greater than 10.8 volts, a battery temperature calculation procedure 508 is performed to determine the temperature of the battery under test. First a fifty-five second time delay is introduced which, when added to the five second period of the lamp test routine 504, yields a total time delay of sixty seconds from the time the switch 144 or 146 was closed. At the end of that sixty second period the temperature of the connector block, T.sub.B, is measured. In the disclosed apparatus, two possible routines are used to determine battery temperature, T.sub.E, depending upon whether the difference between T.sub.A and T.sub.B is greater than 2.degree. F. If that difference is greater than 2.degree. F., the battery temperature is calculated as follows:

If the difference not greater than 2.degree. F., the battery temperature is calculated as follows:

After the battery temperature is determined, that temperature is used as an input to the testing procedure carried out. One example of such test procedures are those disclosed in the aforementioned application Ser. No. 863,925 wherein tests were run on the performance of the battery under load, its bounce back voltage, and on an internal impedance of the battery. In the analyzer of FIGS. 3-7, load and bounce back tests similar to those used in Ser. No. 863,925 are used, but the third test used is one which detects the presence of a bad cell within the battery under test and is more fully described and discussed in the copending application of T. J. Dougherty, C. J. Frailing and R. T. Johnson entitled "Automatic Battery Analyzer Including Apparatus for Determining the Presence of a Single Bad Cell", and being filed contemporaneously herewith. As the first step in performing the load and bounce back voltage tests, the load and bounce back reference voltages are determined from the determined battery temperatures and stored in memory. The calculated reference voltages are referred to as ERFTMP and EBBTMP in FIG. 7 and Table 1. The relationships between the two reference voltages and battery temperature are shown in FIGS. 4a and 4b of said application Ser. No. 863,925. At the initiation of the load test, light emitting diode 180 is illuminated to indicate that the load test is in progress and the cold cranking rating of the battery is read from the potentiometer 136 previously adjusted by the operator to correspond to the cold cranking rating of the battery under test. That rating is a value in amperes and is the current the battery is intended to be able to deliver for a period of thirty seconds at zero degrees Fahrenheit without the battery terminal voltage falling below 7.2 volts for a conventional, six-cell, twelve volt lead-acid storage battery. The relays in the load bank relays 120 are then closed to place the corresponding resistances across the battery under test and load it to deliver a current of approximately one-half its cold cranking rating. The battery current is monitored by measurement of the voltage across the shunt 116 and if the difference between the actual current and one-half the cold cranking rating is greater than approximately 9 amperes, the load is altered to bring the current closer to one-half of the cold cranking rating. The battery terminal voltage is measured during the load test. If at the end of twenty seconds that voltage exceeds the previously determined ERFTMP the battery under test is assumed to be acceptable, the load is removed from the battery, light emitting diodes 180 and 170 are extinguished, light emitting diode 178 is energized to indicate that the battery under test has been determined to be acceptable, and the tester returns to loops 500 and 502 in preparation for the next test. If the battery terminal voltage falls below ERFTMP at any time during the load test, the battery is assumed to have failed the load test, light emitting diode 180 is extinguished, and the load is removed from the battery. In the event that load test failure occured while the battery under test is being retested and is known to have been fully charged (i.e., the test sequence was initiated by closure of pushbutton switch 146), the battery is then known to be unacceptable. Light emitting diodes 176 and 170 are illuminated and extinguished, respectively, and the analyzer is returned to loops 501 and 502 in preparation for the next test. If the load test failure occurred during an initial test of the battery, the voltage bounce back test is performed by measuring the battery voltage fifteen seconds after termination of the load test. If that measured voltage exceeds EBBTMP, the battery has passed the bounce back voltage test but is assumed to be unacceptable, light emitting diodes 176 and 170 are illuminated and extinguished, respectively, and the analyzer is returned to loops 500 and 502 in preparation for the next test. If that measured voltage is less than EBBTMP, the condition of the battery is still undertermined and the test to determine the presence of a bad cell is performed.

The first step in the bad cell detection test is to clear a register labelled BATVL. A temperature corrected standard voltage, BATVTC, is then calculated as follows:

A fixed resistance load of 0.1 ohm then placed across the battery by closing the contact pair 314. After a five second delay, a loop procedure 520 is executed during which the voltage across the battery terminals is measured each second and the result of each voltage measurement is compared with the voltage measurement made the previous second.

In the case of a normally operating battery, the voltage supplied to a fixed resistance load is a monotonically decreasing function of time after an initial period of discharge. Here the initial period is taken as five seconds. After that initial period and while the constant resistance load is placed across the battery terminals the terminal voltage measured at any time exceeds the voltage measured in the preceeding second, it is known that the terminal voltage is increasing. The first time the measured battery voltage exceeds the voltage measured the previous second, the previously measured voltage is stored in the BATVL register. That stored voltage is assumed to be the minimum battery voltage. If while the constant resistance load is across the battery terminals, the measured battery terminal voltage exceeds the minimum battery terminal voltage by 0.17 volts, the battery is assumed to have a bad cell and thus to be unacceptable, light emitting diode 176 is illuminated, the relay contacts 314 are opened to remove the load from the battery, light emitting diode 170 is extinguished, and the tester returns to loops 500 and 502 in preparation for the next test.

Loop 520 is also exited after a ten second time period at point 524. If at that time the battery terminal voltage measured during the proceeding second exceeds the previously determined BATVTC, the battery is assumed to be acceptable but in need of a recharge before being returned to service; in this case light emitting diode 174 is illuminated to make the proper indication to the operator, relay contacts 316 are opened to remove the load from the battery, light emitting diode 170 is extinguished, and the tester returns to loops 500 and 502 in preparation for the next test. If at that same time the battery terminal voltage measured during the proceeding second does not exceed the previously determined BATVTC, a loop 526 is entered which is quite similar to the loop 520 and carries out the constant resistance load test for another five seconds while continuing to look for increases in the battery terminal voltage. If the battery terminal voltage should increase during that additional five second period and if the battery terminal voltage should exceed by 0.17 volts the minimum value thereof obtained during either that period or the previous 10 second period, the battery is again assumed to have a bad cell and to be unacceptable, light emitting diode 176 and 170 are illuminated and extinguished, respectively, the load is removed from the battery, and the tester returns to loops 500 and 502 in preparation for the next test. If during that additional five second period the battery is not thus determined to be unacceptable, then it is assumed that insufficient information concerning the battery is available to determine its condition and the battery must be recharged and retested to determine its acceptability. In this case, light emitting diode 172 is illuminated to give the proper indication, the load is removed from the battery, light emitting diode 170 is extinguished, and the tester returned to loops 500 and 520 in preparation for the next test.

A program for the 6802 microprocessor in assembly language to execute the program of the flow charts of FIGS. 7a-7e is at Table I as follows: ##SPC1## ##SPC2## ##SPC3##

It will thus be seen that a completely automatic battery temperature measuring circuit has been provided which requires no activities to be performed by the user as well as a battery analyzing apparatus making use of the battery temperature measuring circuit. The battery temperature measuring circuit is effective to measure the temperature of a connector attached to the battery post at a time just prior to attachment of the connector to the battery under test and at the end of a time period following attachment of the connector to the battery under test. Thus, the measured temperature is relatively uneffected by such things as the heat of the operator's hand which might tend to warm the battery connector as the operator secured the connector to the battery post. It has been found in practice that the battery temperature measuring circuit of this invention gives considerably greater accuracy than apparatus of the prior art which, for instance, attempted to measure the temperature of the battery post rather than the temperature of the battery connector and utilized the temperature of the battery post at a time immediately following attachment of the connector to the battery post thus completely ignoring any information available concerning the ambient temperature. Further, the temperature measuring apparatus disclosed requires no access whatsoever to the interior of the battery under test and may make use of a battery connector which is relatively small and may be used with a wide variety of battery types. Finally, the temperature measuring apparatus does not require an excessively long time to determine the battery temperature. There has further been provided a battery analyzing apparatus including such a temperature measuring circuit which is effective to alter the tests performed on the battery in response to the battery temperature.

While a particular embodiment of this invention has been described, it will be understood, of course, that the invention is not to be limited thereto since modification may be made by those skilled in the art, particularly in light of the foregoing teachings. As an example, the second measurement of the connector block temperature might be made at the end of the fixed time period following attachment of the battery testing apparatus to the battery under test rather than at the end of a fixed time period following initiation of the battery test procedure by the operator. As a further example, the second measurement of the connector block temperature might be at the end of a time period of variable length so that, for example, the period required to measure the battery temperature could be considerably shortened where the battery temperature is relatively close to the ambient temperature. As a still further example, the ambient temperature could be measured using a second temperature sensor placed at a physical location other than the connector block so that any effect of handling of the connector block by the operator on the determined battery temperature could be further reduced. And as a last example, since the determined battery temperature is only used to determine the magnitude of other reference voltages for use by the battery analyzer, it is also possible that the intermediate step of determining the battery temperature could be eliminated and the reference voltages determined directly from the measured ambient and connector block temperatures. It is contemplated by the appended claim to cover any such modifications as full within the true spirit and scope of this invention: