STAND ALONE SOLAR BATTERY CHARGER

• US 20110199040A1
• Filed: 02/12/2010
• Published: 08/18/2011
• Est. Priority Date: 02/12/2010
• Status: Active Grant

• Current Assignee: Knobbe Martens Olson & Bear LLP
• Original Assignee: Suncore, Inc.
• Inventors: Brimmer, Steven R., Sanett, Richard E., English, Peter
• Granted Patent: US 8,319,470 B2
• Time in Patent Office: Days
• US Class Current: 320/101
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02S 40/38 Energy storage means, e.g. batteries, structurally associated with PV modules
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 70/30 Systems combining energy storage with energy generation of non-fossil origin

Abstract

A portable solar battery charger comprises a photovoltaic array, a power regulator, a controller, and a battery. In one embodiment, the controller is configured to increase the charging current provided by the power regulator to the battery over time using discrete current levels. A comparator can compare the voltage of the photovoltaic array to a threshold, and provide the result to the controller. The controller can be configured to decrease the current to a previously selected level when the comparator indicates the voltage of the photovoltaic array is below a threshold, thereby improving the efficiency of the current delivery to the battery.

Claims

1. An apparatus for charging a battery, the apparatus comprising:

a photovoltaic array for generating power from electromagnetic radiation;

a monitoring circuit configured to compare the voltage at the photovoltaic array to a threshold voltage and to generate a comparison signal based on the comparison;

a charging circuit configured to draw a charging current from the photovoltaic array and to make the charging current available to the battery; and

a control circuit configured to receive the comparison signal and to control the charging circuit, wherein the control circuit is configured to direct the charging circuit to generate a charging current of a first amplitude at a first time, and wherein the control circuit is configured to direct the charging circuit to increase the charging current from the first amplitude to a second amplitude at a second time, and wherein the control circuit is configured to direct the charging circuit to decrease the charging current from the second amplitude to the first amplitude at a third time if the comparison signal indicates that the voltage at the photovoltaic array is less than that threshold voltage at the third time,

wherein the threshold voltage is selected such that when the comparison signal indicates that the voltage at the photovoltaic array is less than that threshold voltage at the third time, the first amplitude is equal to about the amplitude of a current at maximum power of the photovoltaic array at the third time.

2. The apparatus of claim 1, wherein the control circuit is further configured to direct the charging circuit to increase the charging current from the second amplitude to a third amplitude at a fourth time, if the comparison signal indicates that the voltage at the photovoltaic array is not less than that threshold voltage at the third time.

3. The apparatus of claim 1, further comprising a lithium based battery.

4. The apparatus of claim 3, wherein the threshold voltage is selected to be in the range of about 3.30 V and 3.80 V.

5. The apparatus of claim 3, wherein the difference between the first and second times is selected to be in the range of about 50 ms to 200 ms.

6. The apparatus of claim 3, wherein the difference between the second and third times is selected to be in the range of about 1 ms and 10 ms.

7. The apparatus of claim 1, further comprising an interface adapted to receive a user device and configured to provide the user device a current from the battery.

8. The apparatus of claim 7, wherein the interface is a USB interface.

9. The apparatus of claim 7, further comprising a boost converter adapted to regulate the voltage at the interface.

10. The apparatus of claim 1, further comprising a memory, and wherein the control circuit is further configured to direct the charging circuit to increase the charging current from the first amplitude to the second amplitude by an amount equal to a current step size stored in the memory.

11. The apparatus of claim 1, wherein the control circuit and the charging circuit are configured to communicate using an I²C interface.

12. The apparatus of claim 1, wherein the charging circuit is a switching regulator configured to charge the battery using a constant-current/constant-voltage algorithm.

13. A method of charging a battery, the method comprising:

generating power from electromagnetic radiation using a photovoltaic cell;

drawing a charging current having a first amplitude from the photovoltaic cell;

increasing the amplitude of the charging current from the first amplitude to a second amplitude;

comparing the voltage at the photovoltaic cell to a threshold voltage;

decreasing the charging current from the second amplitude to the first amplitude if the voltage at the photovoltaic cell is less than the threshold voltage; and

making the charging current available to the battery,

wherein drawing the charging current having the first amplitude, increasing the amplitude of the charging current, comparing the voltage at the photovoltaic cell, decreasing the charging current, and making the charging current available to the battery are performed during a first window of time.

14. The method of claim 13, wherein drawing the charging current having the first amplitude, increasing the amplitude of the charging current, comparing the voltage at the photovoltaic cell, decreasing the charging current, and making the charging current available to the battery are repeated during a second window of time, and wherein the first window of time and the second window of time are non-overlapping.

15. The method of claim 13, further comprising increasing the amplitude of the charging current from the second amplitude to a third amplitude if the voltage at the photovoltaic cell is not less than the threshold voltage.

16. The method of claim 13, further comprising displaying information indicative of the amplitude of the charging current on a display.

17. The apparatus of claim 16, further comprising determining the level of charge stored on the battery, and displaying information indicative of the level of charge on the display.

18. An apparatus for charging a battery to a target voltage, the apparatus comprising:

a photovoltaic array for generating power from electromagnetic radiation;

a monitoring circuit configured to compare the voltage at the photovoltaic array to a threshold voltage and to generate a comparison signal based on the comparison;

a charging circuit configured to draw a charging current from the photovoltaic array and to make the charging current available to the battery; and

a control circuit configured to receive the comparison signal and to calibrate the amplitude of the charging circuit, wherein the control circuit is configured to calibrate the amplitude of the charging current to a first amplitude at a first time using the comparison signal, and wherein the first amplitude is equal to about the amplitude of a current at maximum power of the photovoltaic array at the first time, and wherein the control circuit is configured to periodically calibrate the amplitude of the charging current until the voltage of the battery is equal to about the target voltage.

19. The apparatus of claim 18, wherein the apparatus is configured to calibrate the amplitude of the charging current after the voltage of the battery is equal to about the target voltage, if the comparison signal indicates that the voltage at the photovoltaic array is less than the threshold voltage.

20. The apparatus of claim 18, wherein the control circuit is configured to periodically calibrate the amplitude of the charging current at least about every 35 s.

21. A method of charging a battery to a target voltage, the method comprising:

generating power from electromagnetic radiation using a photovoltaic cell;

drawing a charging current from the photovoltaic cell;

making the charging current available to the battery,

comparing the voltage at the photovoltaic cell to a threshold voltage to generate a comparison signal; and

calibrating the charging current to an amplitude equal to about the amplitude of a current at maximum power of the photovoltaic array using the comparison signal,

wherein calibrating the charging current is repeated periodically until the voltage of the battery is equal to about the target voltage.

22. The method of claim 21, further comprising regulating the battery voltage during a voltage regulation phase to equal the target voltage until the charging current reaches a termination current level.

23. The method of claim 22, further comprising calibrating the charging during the voltage regulation phase.

24. A computer-readable storage media comprising instructions, which when executed by a processor, operate to charge a battery, the computer-readable storage media comprising:

instructions for drawing a charging current from a photovoltaic cell;

instructions for comparing the voltage at the photovoltaic cell to a threshold voltage and to generate a comparison signal; and

instructions for periodically calibrating the amplitude of the charging circuit at a multitude of times using the comparison signal, wherein the amplitude at each time is equal to about the amplitude of a current at maximum power of the photovoltaic array at each time.

25. A battery charger comprising:

a photovoltaic array having a first face adapted to receive light and a second face opposite the first face;

a first body portion having an opening therethrough, wherein the opening is configured to allow light to reach the first face of the photovoltaic array;

a second body portion, wherein the second body portion is mateable with the first body portion along a parting plane running substantially parallel to a plane containing the mouth of the opening;

a redistribution layer configured to electrically connect to the second face of the photovoltaic array;

a battery;

a heat sink positioned between the battery and the photovoltaic array, wherein the heat sink is configured to absorb thermal energy emanating from the photovoltaic array;

a printed circuit board having at least one integrated circuit, wherein the printed circuit board is configured to electrically connect to the battery and the redistribution layer; and

a display, wherein the display is configured to be visible through the opening of the first body portion,

wherein when the first and second body portions are assembled, the first and second body portions define a cavity containing the PV array, the redistribution layer, the battery, the heat sink, the printed circuit board, and the display.

26. A battery charger for efficiently charging a multitude of user devices over a plurality of lighting conditions, the battery charger comprising:

a battery;

a photovoltaic array for generating power from electromagnetic radiation;

a charging circuit configured to draw a charging current from the photovoltaic array and to make the charging current available to the battery;

an interface for providing charge from the battery to at least one of the multitude of user devices; and

a microcontroller configured to select the amplitude of the charging current,

wherein the microcontroller is configured to periodically calibrate the amplitude of the charging current to an amplitude which is equal to about the amplitude of a current at maximum power of the photovoltaic array, thereby efficiently charging the multitude of user devices over the plurality of lighting conditions.