Apparatus and method for managing a backup power supply for an aircraft cockpit voice recorder

1. A method for operating a backup power supply which has a capacitor and which provides electrical power to a consuming device when electrical power from a primary source is unavailable, said method comprising:

defining a target energy level for the capacitor;

commencing to charge the capacitor;

measuring a first amount of energy that is stored in the capacitor during charging of the capacitor;

terminating charging the capacitor when the first amount of energy stored in the capacitor reaches the target energy level;

upon electrical power from the primary source becoming unavailable, discharging the capacitor into the consuming device;

measuring an amount of time during which the discharging occurs; and

adjusting the target energy level in response to the amount of time.

2. The method as recited in claim 1 wherein measuring an amount of time occurs from commencement of the discharging until a voltage provided by the backup power supply decreases to a predefined level.

3. The method as recited in claim 1 wherein measuring an amount of time occurs from commencement of the discharging until the consuming device ceases acceptable operation.

4. The method as recited in claim 1 wherein measuring a first amount of energy comprises:

periodically sensing voltage across the capacitor and electric current used to charge the capacitor, thereby producing a voltage value and an electric current value;

deriving a power value from the voltage value and the electric current value; and

employing the power value to derive a measurement of the first amount of energy.

5. The method as recited in claim 1 wherein adjusting the target energy level is in response to deviation of the amount of time from a reference value.

6. The method as recited in claim 5 wherein the reference value corresponds to an amount of time that operation of the consuming device is desired to continue after electrical power from the primary source becomes unavailable.

7. The method as recited in claim 1 further comprising measuring a second amount of energy that is discharged from the capacitor into the consuming device which thereby produces a discharge energy value; and wherein adjusting the target energy level comprises deriving a new value for the target energy level in response to the discharge energy value and deviation of the amount of time from a reference value.

8. The method as recited in claim 7 wherein the new value for the target energy level is derived by altering the discharge energy value in proportion to the deviation of the amount of time from the reference value.

9. The method as recited in claim 1 further comprising after terminating charging the capacitor:

occasionally sensing voltage across the capacitor, and

if that sensed voltage is less than a given voltage level, recharging the capacitor until voltage across the capacitor reaches the given voltage level.

10. The method as recited in claim 9 wherein the given voltage level is determined by sensing voltage across the capacitor when the first amount of energy stored in the capacitor reaches the target energy level.

11. The method as recited in claim 1 further comprising:

sensing a temperature proximate to the backup power supply; and

when the temperature exceeds a given threshold:

(a) defining a desired energy level as a function of the target energy level and the temperature, and

(b) terminating charging the capacitor when the amount of energy stored in the capacitor reaches the desired energy level.

12. The method as recited in claim 11 wherein the desired energy level is related to the target energy level inversely to a relationship between the temperature and the given threshold.

13. A method for operating a backup power supply which has a capacitor and which provides electrical power to a recorder in an aircraft when power from a primary source is unavailable, said method comprising:

commencing to charge the capacitor;

measuring a first amount of energy that is stored in the capacitor during charging of the capacitor;

discontinuing to charge the capacitor when the first amount of energy reaches a threshold energy level;

upon electrical power from the primary source becoming unavailable, conveying electrical current from the capacitor to the recorder, thereby discharging energy from the capacitor;

measuring a second amount of energy that is discharged from the capacitor;

measuring an amount of time during which discharging occurs; and

altering the threshold energy level in response to deviation of the amount of time from a reference value.

14. The method as recited in claim 13 wherein measuring a first amount of energy comprises:

periodically sensing voltage across the capacitor and electric current used to charge the capacitor, thereby producing a plurality of voltage values and a plurality of electric current values;

deriving at least one power value from the plurality of voltage values and the plurality of electric current values; and

employing each power value to derive a measurement of the first amount of energy.

15. The method as recited in claim 13 wherein measuring an amount of time occurs from commencement of the discharging until a voltage provided by the backup power supply decreases to a predefined level.

16. The method as recited in claim 13 wherein the reference value is an amount of time that operation of the recorder is desired to continue after electrical power from the primary source becomes unavailable.

17. The method as recited in claim 13 further comprising:

sensing a temperature proximate to the backup power supply; and

defining the threshold energy level in response to an amount that the temperature exceeds a defined threshold.

18. The method as recited in claim 17 wherein the threshold energy level is decreased in proportion to amount that the temperature exceeds a defined threshold.

19. A method for operating a backup power supply which has a capacitor and which provides electrical power to a consuming device when electrical power from a primary source is unavailable, said method comprising:

charging the capacitor;

discharging the capacitor into the consuming device;

measuring an amount of time during which the discharging occurs;

measuring a first amount of energy that was discharged from the capacitor;

defining a target energy level in response to the amount of time and the first amount of energy;

thereafter, commencing to charge the capacitor;

measuring a second amount of energy that is stored in the capacitor during charging of the capacitor;

terminating charging the capacitor when the second amount of energy reaches the target energy level.

20. The method as recited in claim 19 wherein measuring an amount of time occurs from commencement of the discharging until a voltage provided by the backup power supply decreases to a predefined level.

21. The method as recited in claim 19 wherein measuring a first amount of energy comprises:

periodically sensing voltage across the capacitor and electric current used to charge the capacitor, thereby producing a voltage value and an electric current value;

deriving a power value from each pair of a voltage value and an electric current value; and

employing a plurality of the power values to derive a measurement of the first amount of energy.

22. The method as recited in claim 19 wherein the target energy level is defined as a function of deviation of the amount of time from a reference value.

23. The method as recited in claim 19 wherein the target energy level is defined by altering the first amount of energy based on how much the amount of time deviates from a reference value.

24. The method as recited in claim 19 further comprising:

sensing a temperature proximate to the backup power supply; and

when the temperature exceeds a defined threshold:

(a) defining a desired energy level as a function of the target energy level and the temperature, and

(b) terminating charging the capacitor when the amount of energy stored in the capacitor reaches the desired energy level.

25. The method as recited in claim 24 wherein the desired energy level is related to the target energy level inversely to a relationship between the temperature and the defined threshold.