Battery parameter measurement

• US 6,167,349 A
• Filed: 04/02/1998
• Issued: 12/26/2000
• Est. Priority Date: 04/02/1998
• Status: Expired due to Fees

• Current Assignee: Btech, Inc.
• Original Assignee: Btech, Inc.
• Inventors: Alvarez, Jose A.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): BARBEE, MANUEL L
• Application Number:
  US09/053,906
• Time in Patent Office: 999 Days
• Field of Search: 702/63, 702/64, 702/FOR 103-105, 320/126, 320/132, 320/134, 320/136, 324/425-427, 324/429, 324/430, 324/432, 324/434, 324/444
• US Class Current: 702/63
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery

Abstract

A method and system for evaluating lead-acid battery jars in a battery backup or standby system applies, in a stepwise manner, a current load across a group of adjacent jars. Voltage measurements are taken across each jar in the group at various times during the application of the current load. These measurements are utilized to calculate the ohmic resistance, the charge transfer resistance and the double layer capacitance of each jar.

Claims

1. A method for evaluating a battery jar, comprising the steps of:

a) applying a measured current load to said battery jar in a stepwise manner;

b) measuring the voltage across said battery jar before said current load is applied;

c) measuring the voltage across said battery jar at least once during the application of said current load;

d) determining, from the at least one voltage measurement from the step c), the voltage across said battery jar immediately after said current load is applied;

e) calculating, from the measured voltage from the step b) and the determined voltage from the step d), the ohmic resistance of said battery jar;

f) measuring the voltage across said battery jar at least once more during the application of said current load if the step c) provided only one measurement;

g) determining, from at least the second voltage measurement from the steps c) and f), the steady state voltage across said battery jar in response to said current load; and

h) calculating, from the determined steady state voltage from the step g) and the determined voltage from the step d), the charge transfer resistance of said battery jar;

wherein the step a) of applying a measured current load includes the steps of;

a1) providing a first series of pulses of said measured current and each of a first duration; and

a2) providing a second series of pulses of said measured current and each of a second duration;

wherein the step e) of calculating the ohmic resistance utilizes measurements taken during said first series of pulses;

wherein the step h) of calculating the charge transfer resistance utilizes measurements taken during said second series of pulses; and

wherein said second duration is greater than said first duration.

2. The method according to claim 1 wherein:

said first duration is in the range from about 0.5 ms to about 10 ms; and

said second duration is in the range from about 1 ms to about 50 ms.

3. The method according to claim 1 wherein the step e) of calculating the ohmic resistance includes the step of:

e1) calculating the voltage difference between the measured voltage from the step b) and the determined voltage from the step d).

4. The method according to claim 3 further including the steps of:

i) measuring the current applied to said battery jar during the step a); and

the step e) of calculating the ohmic resistance further includes the step of;

e2) dividing the voltage difference from the step el) by the measured current from the step i).

5. The method according to claim 1 wherein the step h) of calculating the charge transfer resistance includes the step of:

h1) calculating the voltage difference between the determined voltage from the step g) and the determined voltage from the step d).

6. The method according to claim 5 further including the step of:

i) measuring the current applied to said battery jar during the step a); and

the step h) of calculating the charge transfer resistance further includes the step of;

h2) dividing the voltage difference from the step h1) by the measured current from the step i).

7. The method according to claim 1 further comprising the steps of:

i) utilizing a curve fitting technique to determine, from the at least two voltage measurements from the steps c) and f), the time constant of the voltage response of said battery jar to the stepwise application of the current load; and

j) calculating, from the determined time constant from the step i) and the calculated charge transfer resistance from the step h), the double layer capacitance of said battery jar.

8. The method according to claim 7 wherein the step j) of calculating the double layer capacitance includes the step of:

j1) dividing the time constant from the step i) by the charge transfer resistance from the step h).

9. A system for evaluating each of a plurality of rechargeable battery jars arranged in at least one string of serially connected jars, the strings being connected in parallel when there are at least two such strings, the jars of each string being divided into at least two groups, the system comprising:

a switchable current load;

a first controllable switch bank associated with each of the strings and controllable for selectively coupling in a stepwise manner the current load across a selected group of adjacent jars in said each string;

a bus system;

a voltage measurement module coupled to the bus system and associated with each group of adjacent jars in each string, the voltage measurement module including a pair of voltage measurement terminals and a second controllable switch bank associated with the jars of said each group and controllable for selectively coupling one jar of said each group at a time across said pair of terminals, the voltage measurement module being effective to collect data indicative of the voltage across said pair of terminals;

a current measurement system coupled to the bus system and coupled to the switchable current load to collect data indicative of load current;

a controller coupled to the bus system and effective to control the operation of the current load and the first controllable switch bank, the controller being further effective to transmit control signals over the bus system to actuate in turn each voltage measurement module to control the second controllable switch bank and collect voltage data from the jars of the associated said each group of jars, the controller further collecting load current data over the bus system from the current measurement system; and

a computer coupled to the controller and effective to cause the controller to control the current load, the first controllable switch bank, each voltage measurement module and the current measurement system so that a current load is applied in a stepwise manner to said each group of adjacent jars one at a time, the voltage measurement module associated with that group collects voltage data from each jar during the stepwise application of load current to that group, and the current measurement system collects current measurement data, the computer being further effective to collect all of the voltage and current measurement data and to utilize the collected data to calculate at least one of the ohmic resistance, the charge transfer resistance and the double layer capacitance for each of the jars;

wherein the voltage measurement module includes;

a plurality of low pass filters;

a first plurality of switches each connected between one of said pair of voltage measurement terminals and a respective one of said low pass filters;

an analog to digital converter;

a second plurality of switches each connected between a respective one of said low pass filters and said analog to digital converter;

a connection between the other of said pair of voltage measurement terminals and said analog to digital converter; and

a switch controller arranged so that said first plurality of switches are all initially closed and said second plurality of switches are all initially open, said first plurality of switches are sequentially opened to cause a time-related sequence of voltage measurements to be held in said plurality of low pass filters, and said second plurality of switches are sequentially closed to transfer the time-related sequence of voltage measurements to the analog to digital converter.

10. The system according to claim 9 wherein the controller includes an internal real time clock and is effective to autonomously initiate voltage and current data measurement by the voltage measurement modules and the current measurement system at predetermined specific time intervals at predetermined specific times for subsequent collection by the computer.

11. A system for evaluating each of a plurality of rechargeable battery jars arranged in at least one string of serially connected jars, the strings being connected in parallel when there are at least two such strings, the jars of each string being divided into at least two groups, the system comprising:

a switchable current load;

a first controllable switch bank associated with each of the strings and controllable for selectively coupling in a stepwise manner the current load across a selected group of adjacent jars in said each string;

a bus system;

a voltage measurement module coupled to the bus system and associated with each group of adjacent jars in each string, the voltage measurement module including a pair of voltage measurement terminals and a second controllable switch bank associated with the jars of said each group and controllable for selectively coupling one jar of said each group at a time across said pair of terminals, the voltage measurement module being effective to collect data indicative of the voltage across said pair of terminals;

a current measurement system coupled to the bus system and coupled to the switchable current load to collect data indicative of load current;

a controller coupled to the bus system and effective to control the operation of the current load and the first controllable switch bank, the controller being further effective to transmit control signals over the bus system to actuate in turn each voltage measurement module to control the second controllable switch bank and collect voltage data from the jars of the associated said each group of jars, the controller further collecting load current data over the bus system from the current measurement system; and

a computer coupled to the controller and effective to cause the controller to control the current load, the first controllable switch bank, each voltage measurement module and the current measurement system so that a current load is applied in a stepwise manner to said each group of adjacent jars one at a time, the voltage measurement module associated with that group collects voltage data from each jar during the stepwise application of load current to that group, and the current measurement system collects current measurement data, the computer being further effective to collect all of the voltage and current measurement data and to utilize the collected data to calculate at least one of the ohmic resistance, the charge transfer resistance and the double layer capacitance for each of the jars;

wherein the switchable current load includes a sensing resistance, and the current measurement system includes;

a plurality of low pass filters;

a first plurality of switches each connected between a first side of said sensing resistance and a respective one of said low pass filters;

an analog to digital converter;

a second plurality of switches each connected between a respective one of said low pass filters and said analog to digital converter;

a connection between the other side of said sensing resistance and said analog to digital converter; and

a switch controller arranged so that said first plurality of switches are all initially closed and said second plurality of switches are all initially open, said first plurality of switches are sequentially opened to cause a time-related sequence of voltage measurements to be held in said plurality of low pass filters, and said second plurality of switches are sequentially closed to transfer the time-related sequence of voltage measurements to the analog to digital converter.

12. The system according to claim 11 wherein the controller includes an internal real time clock and is effective to autonomously initiate voltage and current data measurement by the voltage measurement modules and the current measurement system at predetermined specific time intervals at predetermined specific times for subsequent collection by the computer.