METHOD AND APPARATUS FOR DETERMINING BATTERY PERFORMANCE AT ONE TEMPERATURE WHEN BATTERY IS AT ANOTHER TEMPERATURE

• US 3,781,658 A
• Filed: 01/14/1972
• Issued: 12/25/1973
• Est. Priority Date: 01/14/1972
• Status: Expired due to Term

• Current Assignee: James B. Godshalk
• Original Assignee: James B. Godshalk
• Inventors: Godshalk, James B.
• Primary Examiner(s): Corcoran, Robert J.
• Application Number:
  US05/217,760
• Time in Patent Office: 711 Days
• Field of Search: 324/29.5 320/48 340/249
• US Class Current: 324/431
• CPC Class Codes: G01R 31/005 Testing of electric installations on transport means
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/385 Arrangements for measuring battery or accumulator variables for monitoring G01R31/382
• CPC Class Codes: G01R 31/386 using test-loads
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Both a method and apparatus are disclosed for testing lead-acid storage batteries to determine the cranking amperes which the battery can supply at a predetermined low temperature, typically 0*F., when the battery is in fact at a different temperature. The invention derives from the battery, after a short discharge at substantially its cranking ampere rating, an electrical quantity representative of the actual terminal voltage of the battery at the end of the discharge, and converts this electrical quantity into an observable indication representing the terminal voltage which the battery would exhibit if similarly tested at the predetermined low temperature. The invention is based on the discovery that the terminal voltage of a lead-acid storage battery under load changes predictably with changes in temperature of the battery.

Claims

1. The method for testing a lead-acid storage battery to determine, with accuracies at least adequate for automotive service station battery testing purposes, whether the battery is capable of delivering a stated cranking current at a predetermined temperature when the battery is in fact at a different temperature, comprising discharging the battery substantially at said stated current for a short period of time;

deriving from the battery while it is still being so discharged an electrical quantity representative of the actual terminal voltage of the battery at the end of said period of time;

determining the actual temperature of the battery;

converting said electrical quantity into an observable indication which differs from that which would accurately indicate the actual terminal voltage of the battery by an amount corresponding to the value obtained by determining, from a curve falling within area A, FIG. 3, and representing terminal cell voltage versus battery temperature substantially at rated constant discharge current, the difference between the voltage values of the curve at the predetermined actual temperature of the battery and at said predetermined temperature; and

comparing said indication with that which should be exhibited by the battery if capable of supplying said stated current when at said predetermined temperature.

2. The method according to claim 1, wherein the predetermined temperature is 0* F.;

the test is carried out with the battery at a temperature greater than 0* F.; and

said electrical quantity is the terminal voltage of the battery in volts per cell; and

said step of converting said electrical quantity into an observable indication comprises changing said electrical quantity by an amount Tp/M volts per cell, where T the actual temperature of the battery, in degrees Fahrenheit, at the time of testing, p 0.5, and M a value selected from the range 26-36 to provide a desired test accuracy.

3. The method according to claim 1, wherein said curve is one of a family of curves which includes a first curve comprising a series of straight line segments including a first segment commencing at 0.97 volts at -20* F. and extending to 0* F. with a slope of 0.0015 volts per *F., a second segment commencing at 0* F. at the end of said first segment and extending to 20* F. with a slope of 0.007 volts per *F., a third segment commencing at 20* F. at the end of said second segment and extending to 40* F. with a slope of 0.0035 volts per *F., a fourth segment commencing at 40* F. at the end of said third segment and extending to 60* F. with a slope of 0.0025 volts per *F., and a fifth segment commencing at 60* F. at the end of said fourth segment and extending to 120* F. with a slope of 0.0015;

and the like curves defined by voltage values within + or - 10 percent of the voltage values of said first curve.

4. The method according to claim 1 adapted to be practiced in automotive service station battery testing, wherein said predetermined temperature is 0*F., and said curve is a straight line with a slope of 0.0026-0.0032 volts per +F.

5. The method according to claim 1 adapted to be practiced in automotive service station battery testing, wherein said predetermined temperature is 0* F., and said curve is established by the equation E A + KT, wherein E is the battery cell voltage, A is a value selected from the range 1.08-1.32 volts, K is a value selected from the range 0.002-0.004 volts per cell per *F.

6. The method for testing lead-acid storage batteries to determine, with accuracies at least adequate for automotive service station battery testing purposes, the cranking amperes which the battery can supply at a predetermined low temperature when the battery is in fact at a different temperature, comprising:

discharging the battery for a short period of time at a rate at least substantially equal to the cranking ampere rating of the battery;

determining the actual temperature of the battery;

deriving from the battery an electrical quantity representative of the actual terminal voltage of the battery at the end of said period of time;

converting said electrical quantity into an observable indication;

modifying the observable indication in accordance with the temperature of the Battery so that, regardless of the actual temperature of the battery, the indication is equal within + or - 10 percent to that indication which would represent the electrical quantity which would have been derived from the same battery at said predetermined low temperature; and

comparing said indication with that which should be exhibited by the same battery, if capable of providing its rated cranking amperes, at said predetermined low temperature.

7. The method according to claim 6, wherein said predetermined low temperature is 0* F., and the indication which should be provided by the same battery, if capable of providing its rated cranking amperes at 0* F. corresponds to 1.2 volts per cell.

8. The method for determining whether a lead-acid storage battery, installed in an automotive vehicle powered by an internal combustion engine and having a starting motor driven by the battery, will provide adequate power to start the engine if the battery is at 0* F. when the battery is in fact at a temperature higher than 0* F., comprising:

discharging the battery for a short period of time at a predetermined ampere rate substantially equal to the cranking amperes required to start the engine;

determining the actual temperature of the battery;

measuring the terminal voltage of the battery at the end of said short period of time while the battery is still being discharged at said rate;

converting the measured terminal voltage into an observable indication corresponding to what the terminal voltage would have been were the battery at 0* F. by effectively subtracting therefrom a value substantially equal to TP/M volts per cell, where T is the actual temperature of the battery in *F. p 0.5, and M is a value selected from the range 26-36; and

comparing that indication with one which corresponds to 1.2 volts.

9. In an apparatus for testing a lead-acid storage battery to determine, with accuracies at least adequate for automotive service station battery testing purposes, whether the battery is capable of delivering a stated cranking current at a predetermined temperature when the batter is in fact at a different temperature, the combination of:

discharge circuit means comprising means for discharging the battery for a short period of time at a rate at least substantially equal to the stated cranking current; and

test circuit means connectable to the battery and comprising;

thermally responsive means for sensing the actual temperature of the battery, means for deriving from the battery an electrical quantity representative of the actual terminal voltage of the battery while still being discharged at said rate at the end of said short period of time, electro-responsive indicating means connected to respond to said electrical quantity, calibrating means for modifying the indication displayed on said indicating means in accordance with the characteristics normally expected of the battery being tested; and

means including said thermally responsive means for further calibrating said indicating means so that, when the battery is capable of delivering said stated cranking amperes and said indicating means therefore would provide a predetermined indication with the battery at said predetermined temperature, said indicating means provides substantially the same predetermined indication in response to the electrical quantity derived from the battery when the battery is at any other actual temperature in the range of from -20* F. to 120* F.

10. The combination defined in claim 9, wherein said discharge means comprises at least four load resistors, and means for connecting said load resistors selectively to the battery to provide any of a plurality of discharge rates each matching a different stated cranking current.

11. The combination defined in claim 9, wherein said thermally responsive means comprises a thermally responsive impedance, and means whereby said impedance can be associated with the battery to sense the temperature thereof.

12. The combination defined in claim 11, wherein said indicating means is a voltmeter, and said calibrating means constitutes means for decreasing the sensitivity of said voltmeter by a value in the range of 0.002-0.004 volts per cell for each *F. by which the actual temperature of the battery exceeds said predetermined temperature.

13. The combination defined in claim 9, wherein said calibrating means constitutes means for providing a calibrating electrical quantity of one polarity when the actual temperature of the battery is above said predetermined temperature and of the opposite polarity when the temperature of the battery is below said predetermined temperature.

14. The combination defined in claim 13, wherein said discharge circuit means comprises a load resistor of continuously adjustable resistance value.

15. The combination defined in claim 9, wherein said predetermined temperature is 0* F., said indicating means is a voltmeter, said electrical quantity corresponds to terminal voltage of the battery, and said calibrating means constitutes means for providing a change in the indication of said voltmeter amounting to T.5/M volts per cell, where T is the actual temperature in *F., and M is a value selected from the range of 26-36.

16. The combination defined in claim 9, adapted to determine the cranking current capability of the battery at two different temperatures, wherein said indicating means comprises a first voltmeter for providing indications corrected to one of said predetermined temperatures, and a second voltmeter for providing indications corrected to the others of said prdetermined temperatures.

17. The method for testing a lead-acid storage battery to determine, with accuracies at least adequate for automotive service station battery testing purposes, whether the battery is capable of delivering a predetermined current at a predetermined temperature when the battery is in fact at a different temperature, comprising discharging the battery substantially at the predetermined current for a short period of time;

deriving from the battery while it is still being so discharged an electrical quantity representative of the actual terminal voltage ofthe battery at the end of said period of time;

sensing the actual temperature of the battery;

determining the relationship between battery temperature and cell voltage for the type of battery under test over a temperature range which includes both the predetermined temperature and the temperature sensed by said sensing step;

converting said electrical quantity into an observable indication which differs from that which would accurately indicate the actual terminal voltage of the battery by an amount corresponding to the value obtained by the difference between the cell voltage obtained by said determining step for the actual temperature sensed by said sensing step and the cell voltage obtained by said determining step for the predetermined temperature; and

comparing said indication with that which should be exhibited by the battery if capable of supplying the predetermined current at the predetermined temperature.