Battery charger

• US 5,396,163 A
• Filed: 09/11/1992
• Issued: 03/07/1995
• Est. Priority Date: 03/13/1991
• Status: Expired due to Term

• Current Assignee: Ecotality Incorporated (Blink Charging Co.)
• Original Assignee: Inco Limited (Caixa de Previdência Dos Funcionários Do Banco Do Brasil), Norvik Technologies Incorporated
• Inventors: Soltys, Josef V., Nor, Jiri K., Ettel, Victor A.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US07/943,798
• Time in Patent Office: 907 Days
• Field of Search: 320/20, 320/21, 320/23, 320/32, 320/35, 320/39, 320/40, 320/52
• US Class Current: 320/159
• CPC Class Codes: H02J 7/007182 in response to battery voltage

Abstract

A charger for rechargeable cells or batteries utilizes a mechanism whereby resistance-free voltage is continually monitored during periodic current-off intervals in the charging process and compared to an independent reference voltage to prevent overcharge. After a certain degree of charge has been obtained, the current is gradually reduced to a finishing charge. Several means are provided for terminating the finishing charge while avoiding overcharge. Another embodiment of a charger provides for measurement of the resistance-free voltage during the current-off period after sufficient time is allowed for the recombination of any oxygen which may have been produced during charging, thus taking into account inherent variations in cells of the same type.

Claims

1. A method of recharging rechargeable batteries and cells, comprising the steps of:

(a) providing an electrical charging current from a source thereof to an output across which a rechargeable battery or cell may be connected;

(b) periodically interrupting the flow of electrical charging current to said output and determining the resistance free terminal voltage of the rechargeable battery or cell being recharged during the interval when said flow of electrical charging current has been interrupted, and comparing the sensed resistance free voltage with a reference voltage independent of the rechargeable battery or cell being recharged;

(c) wherein for a first fixed and predetermined period of time, said electrical charging current is delivered to said output at the lesser of either a predetermined maximum current value or a current which said rechargeable battery or cell can accept without any substantial rise in its internal temperature;

and wherein following said first fixed period of time said electrical charging current continues to be delivered to said output at said maximum value for a second variable time period which exists for so long as said sensed resistance free voltage of the rechargeable battery or cell being recharged is less than said independent reference voltage, whereby said second variable time period is terminated at the first instance when said sensed resistance free voltage reaches the same value as said independent reference voltage, and said electrical charging current is permitted to reduce in such a manner that the sensed resistance free voltage does not exceed said independent reference voltage;

(d) operating a timer from the beginning of the charge cycle so that (1) following a third predetermined period of time from the beginning of the charge cycle, the electrical charging current is reduced to a predetermined value of from zero to a predetermined low charging current in the event that the charge current is still at said maximum value; and

(2) at the end of a fourth predetermined period of time which follows the instant when the electrical charging current begins to be reduced, the electrical charging current is forcibly altered to a predetermined value of finishing charge current of from zero to a predetermined low charging current which is below said predetermined maximum current value; and

(e) operating a means for terminating the finishing charge;

wherein the means of step (e) comprises a means for measuring the value of total charge delivered to the battery or cell, and wherein the finishing charge is terminated when a predetermined value of total charge delivered has been reached.

2. The method of claim 1, wherein the means of step (e) comprises a timing means, and wherein the finishing charge is terminated at the end of a fifth predetermined period of time measured from the beginning of the fourth period of time, the fifth period of time being a function of the difference between the end of the second period of time and the beginning of the fourth period of time.

3. The method of claim 2, wherein the finishing charge current is about 20% of the value of the electrical charging current in step (a), and the fifth period of time is approximately equal to the difference between the end of the second period of time and the beginning of the fourth period of time.

4. The method of claim 1, wherein the value of total charge delivered is measured from the beginning of the first period of time.

5. The method of claim 1, wherein the value of charge delivered is measured from the beginning of the fourth period of time.

6. The method of claim 1, wherein the means of step (e) comprises a means for detecting changes in the resistance free voltage with respect to time during step (d) (1), and wherein the finishing charge is terminated when said means detects a change in the resistance free voltage which is characteristic of the onset of overcharge.

7. The method of claim 6, wherein the finishing charge is terminated when either of a voltage peak or a voltage plateau in said finishing charge is detected.

8. The method of claim 6, wherein the finishing charge is terminated when a second inflection point in said finishing charge is detected.

9. The method of claim 8, further comprising operating a processing means, wherein said processing means compiles data for values of resistance free voltage with respect to time, and locates said second inflection point by computing the maximum of the first derivative of resistance free voltage with respect to time.

10. The method of claim 8, further comprising operating a means for measuring the value of total charge delivered to the battery or cell, wherein the finishing charge is terminated when a predetermined value of charge delivered has been reached, and wherein said predetermined value of charge being measured is measured from when said second inflection point has been detected.

11. A charger for recharging rechargeable batteries and cells, comprising:

(a) means for providing an electrical charging current from a source thereof to an output across which a rechargeable battery or cell may be connected;

(b) means for periodically interrupting the flow of electrical charging current to said output and determining the resistance free terminal voltage of the rechargeable battery or cell being recharged during the interval when said flow of electrical charging current has been interrupted, and comparing the sensed resistance free voltage with a reference voltage independent of the rechargeable battery or cell being recharged;

(c) wherein for a first fixed and predetermined period of time, said electrical charging current is delivered to said output at the lesser of either a predetermined maximum current value or a current which said rechargeable battery or cell can accept without any substantial rise in its internal temperature;

and wherein following said first fixed period of time said electrical charging current continues to be delivered to said output at said maximum value for a second variable time period which exists for so long as said sensed resistance free voltage of the rechargeable battery or cell being recharged is less than said independent reference voltage, whereby said second variable time period is terminated at the first instance when said sensed resistance free voltage reaches the same value as said independent reference voltage, and said electrical charging current is permitted to reduce in such a manner that the sensed resistance free voltage does not exceed said independent reference voltage;

(d) a timing means which operates from the beginning of the charge cycle so that (1) following a third predetermined period of time from the beginning of the charge cycle, the electrical charging current is reduced to a predetermined value of from zero to a predetermined low charging current in the event that the charge current is still at said maximum value; and

(2) at the end of a fourth predetermined period of time which follows the instant when the electrical charging current begins to be reduced, the electrical charging current is forcibly altered to a predetermined value of finishing charge current of from zero to a predetermined low charging current which is below said predetermined maximum current value; and

(e) a means for terminating the finishing charge;

wherein the means for terminating the finishing charge comprises a means for measuring the value of total charge delivered to the battery or cell, and means for terminating the finishing charge when a predetermined value of total charge delivered has been reached.

12. The charger of claim 11, wherein the means for terminating the finishing charge comprises a timing means, whereby the finishing charge may be terminated at the end of a fifth predetermined period of time measured from the beginning of the fourth period of time, the fifth period of time being a function of the difference between the end of the second period of time and the beginning of the fourth period of time.

13. The charger of claim 12, wherein the finishing charge current is about 20% of the value of the electrical charging current provided from the source thereof, and the fifth period of time is approximately equal to the difference between the end of the second period of time and the beginning of the fourth period of time.

14. The charger of claim 11, comprising means for measuring the value of total charge delivered from the beginning of the first period of time.

15. The charger of claim 11, comprising means for measuring the total charge value from the beginning of the fourth period of time.

16. The charger of claim 11, wherein the means for terminating the finishing charge comprises detecting means for detecting changes in the resistance free voltage with respect to time during step (d) (1), and further comprising means for terminating the finishing charge when said detecting means detects a change in the resistance free voltage which is characteristic of the onset of overcharge.

17. The charger of claim 16, wherein the means for terminating the finishing charge comprises means for detecting when either a voltage peak or a voltage plateau in said finishing charge is detected.

18. The charger of claim 16, wherein the means for terminating the finishing charge comprises means for detecting when a second inflection point in said finishing charge is detected.

19. The charger of claim 18, further comprising a processing means, wherein said processing means compiles data for values of resistance free voltage with respect to time, and locates said second inflection point by computing the maximum of the first derivative of resistance free voltage with respect to time.

20. The charger of claim 18, further comprising a means for measuring total charge delivered to the battery or cell, and further comprising means for terminating the finishing charge when a predetermined value of charge delivered has been reached, wherein said value of charge is measured from when said second inflection point has been detected.