Battery state-of-charge indicator

• US 4,234,840 A
• Filed: 04/13/1979
• Issued: 11/18/1980
• Est. Priority Date: 04/13/1979
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Konrad, Charles E., Davis, Richard K.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US06/029,941
• Time in Patent Office: 585 Days
• Field of Search: 320/39, 320/40, 320/48, 340/636, 324/433, 324/465
• US Class Current: 320/127
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3646 for indicating electrical conditions or variables, e.g. visual or audible indicators
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A circuit for indicating the charge state of a battery supplying discharge current to its load circuit under actual load operation during which battery discharge current is subject to magnitude variations and interruptions, having means for storing a stored signal whose value is representative of battery state-of-charge, means for rapidly increasing the value of the stored signal to the scaled value of the battery terminal voltage when its scaled value is below that of the battery terminal voltage, first means for decreasing the value of the stored signal at a slow rate preestablished such that the stored signal decreases from a first value representative of a fully charged battery to a second value representative of a discharged battery in a time period approximating the average time required during normal operation of the load circuit for the fully charged battery to become discharged, and second means, operative only during intervals when the battery supplies no discharge current to the load, for decreasing the value of the stored signal at a rate intermediate said slow and fast rates and related to the difference between the scaled values of the battery terminal voltage and the stored signal.

Claims

1. A circuit for monitoring the charge state of a battery supplying discharge current to its normal load circuit under actual load operation during which battery discharge current is subject to magnitude variations and interruptions comprising:

(a) battery terminal voltage sensing means adapted to provide a scaled battery voltage signal representative of actual battery terminal voltage;

(b) storage means for storing a stored signal whose value is indicative of the state-of-charge of said battery, said stored signal having predetermined first and second values representative of battery terminal voltage under no-load conditions, said first and said second values being representative, respectively, of the fully charged and discharged battery;

(c) means for coupling said sensing means and storage means solely to increase the value of said stored signal at a rapid first rate to the scaled value of said battery voltage signal during intervals when the scaled value of said battery voltage signal exceeds the value of said stored signal;

(d) means for continuously decreasing the value of said stored signal at a slow second rate, said second rate being pre-established to provide for variation of said stored signal from said first value to said second value in a time period approximating the average time required for the fully charged battery to become discharged during normal operation of the load circuit; and

(e) means responsive to the value of said stored signal for providing an indication of battery state-of-charge, whereby said circuit is operative under conditions of variable battery discharge current and without sensing the magnitude of battery discharge current.

2. The circuit of claim 1, wherein the means for decreasing the stored signal has a pre-established rate providing for variation from said first to said second value in a time period exceeding 30 minutes.

3. The circuit of claim 1, wherein said means for coupling said sensing means and storage means comprises comparison means for comparing the scaled values of said battery voltage and stored signals and means, responsive to said battery voltage signal exceeding said stored signal for increasing the value of said stored signal to the scaled value of said battery voltage signal.

4. The circuit of claim 2 wherein said storage means comprises capacitance means, coupled to be charged by the output of said comparison means.

5. The circuit of claim 4 wherein said means for continuously decreasing the value of said stored signal comprises constant current discharge means coupled in circuit with said capacitance means.

6. The circuit of claim 5 wherein said constant current discharge means comprises resistance means coupled in parallel circuit with said capacitance means, and means for establishing a constant potential across at least a portion of said resistance means to establish a discharge current of predetermined amplitude.

7. The circuit of claim 1 comprising additional means for decreasing the value of said stored signal at a third rate intermediate said first and second rates solely during intervals during which the battery provides no discharge current to the load circuit.

8. The circuit of claim 7 comprising means detecting the presence of battery discharge current for inhibiting said additional means during intervals of battery discharge current.

9. The circuit of claim 8 wherein said third rate is selected such that upon cessation of discharge current, the time interval required for the stored signal to attain the scaled value of said battery voltage signal approximates the time interval required for the battery terminal voltage to attain its no-load value.

10. A circuit adapted for monitoring the charge state of a battery supplying discharge current to its normal load circuit under actual load operation during which the battery discharge current is subject to magnitude variation and interruption, comprising:

(a) a battery terminal voltage sensing means adapted to provide a scaled battery voltage signal;

(b) storage means for storing a stored signal whose value is indicative of the state-of-charge of said battery;

(c) first means for increasing the value of said stored signal to the scaled value of said battery voltage signal at a rapid first rate;

(d) second means for decreasing the value of said stored signal at a slow second rate during intervals of battery discharge current;

(e) third means for decreasing the value of said stored signal at a third rate intermediate said first and second rates during intervals when battery discharge current is interrupted; and

(f) means for utilizing said stored signal to provide an indication representative of the charge state of the battery.

11. The circuit of claim 10, wherein said first means are connected to increase the value of said stored signal solely during intervals when the scaled value of said battery voltage signal exceeds the value of said stored signal.

12. The circuit of claim 11, comprising fourth means for inhibiting operation of said third means during intervals when there is battery discharge current.

13. The circuit of claim 12 for use with an electric motor load circuit, wherein said fourth means comprises means for detection of voltage ripple signals resulting from operation of an electric motor load, and means responsive to detection of such ripple signals for inhibiting operation of said third means.

14. The circuit of claim 10, wherein said second means is constructed to decrease the value of said stored signal at a predetermined rate established such that said stored signal is decreased from a first value representative of the no-load voltage of a fully charged battery to a second voltage representative of no-load voltage of a discharged battery in a time period approximating the average time required for the fully charged battery to become discharged during normal operation of the load circuit.

15. The circuit of claim 14, wherein said third means is constructed such that the value of said stored signal is decreased at a third rate selected such that upon cessation of discharge current the time interval for the stored signal to attain the scaled value of said battery voltage approximates the time interval required for the battery terminal voltage to attain its no-load value.

16. A circuit adapted for monitoring the charge state of a battery supplying discharge current to its normal load under actual load operation during which the battery discharge current is subject to magnitude variation and interruption, comprising:

(a) means for sensing battery terminal voltage to provide a scaled battery voltage signal;

(b) capacitance means for storing a stored signal whose value is indicative of the state-of-charge of said battery;

(c) comparison means for comparing the scaled values of said battery voltage signal and said stored signal, said comparison means comprising an output coupled via unilaterally conducting means to said capacitance means for increasing the value of said stored signal to the scaled value of said battery voltage during intervals when the scaled value of said battery voltage signal exceeds the value of said stored signal;

(d) constant current discharge means coupled in circuit with said capacitance means for continuously decreasing the value of said stored signal at a predetermined slow rate;

(e) additional discharge means coupled in circuit with said capacitance means for decreasing the value of said stored signal at a rate faster than said predetermined slow rate; and

(f) means for sensing the presence of battery discharge current and responsive thereto inhibiting operation of said additional discharge means.