Method For Charging Rechargeable Lithium Accumulators

• US 20090096425A1
• Filed: 10/14/2008
• Published: 04/16/2009
• Est. Priority Date: 10/16/2007
• Status: Active Grant

• Current Assignee: C.&E. Fein GmbH
• Original Assignee: C.&E. Fein GmbH
• Inventors: Barza, Radu, Schreiber, Alfred
• Granted Patent: US 8,378,639 B2
• Time in Patent Office: Days
• US Class Current: 320/156
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient
• CPC Class Codes: H02J 7/007188 the charge cycle being controlled or terminated in response to non-electric parameters

Abstract

A method and a charging device serve for charging rechargeable lithium accumulators. A charging current is injected into the accumulator, and the voltage is monitored on the accumulator during the injection process. Additionally, the variation in time of at least one state variable characteristic of the accumulator is monitored and injection of the charging current into the accumulator is continued until the variation in time of the state variable exceeds a predefined limit value.

Claims

1. A method for charging a rechargeable lithium accumulator, comprising the steps of:

injecting a charging current into the accumulator;

monitoring a voltage of the accumulator during the injection process;

monitoring a variation in time of at least one state variable characteristic of the accumulator;

continuing the injection of the charging current into the accumulator until a variation in time of said state variable exceeds a predefined threshold value.

2. The method of claim 1, wherein said charging current is controlled along a predefined time characteristic.

3. The method of claim 2, wherein said charging current is kept constant over time.

4. The method of claim 2, wherein said charging current is periodically shaped.

5. The method of claim 4, wherein said charging current is pulsed.

6. The method of claim 1, wherein said variation in time of said state variable that is monitored is selected from the group consisting of a variation in time of a voltage (dU/dt), a variation in time of a temperature (dT/dt), and a variation in time of an internal resistance (dR_i/dt) of said accumulator.

7. The method of claim 1, wherein at least two state variables of said accumulator are monitored at the same time, and wherein injection of the charging current into the accumulator is continued until one of the variations in time of the at least two state variables exceeds the respective associated predefined threshold value.

8. The method of claim 1, wherein a rise in time of said state variable is monitored.

9. The method of claim 8, wherein said variation in time of said state variable that is monitored is selected from the group consisting of a rise in time of said voltage, a rise in time of said temperature, and a rise in time of said inner resistance of said accumulator.

10. The method of claim 1, wherein the charging current is switched off when the variation in time of the state variable exceeds the predefined threshold value.

11. The method of claim 1, wherein the charging current is gradually reduced to zero when the variation in time of the state variable exceeds the predefined threshold value.

12. The method of claim 1, wherein a lithium iron phosphate accumulator is charged.

13. The method of claim 1, wherein the accumulator is configured for powering an electric power tool.

14. The method of claim 9, wherein the charging current is switched off when the variation in time of the state variable exceeds said predefined threshold value.

15. A charging device for charging a rechargeable lithium accumulator having first means for injecting a charging current into the accumulator and second means for monitoring the voltage on the accumulator during the injection process, wherein third means are provided for additionally monitoring the variation in time of at least one state variable characteristic of the accumulator, and wherein means are provided for continuing injection of the charging current into the accumulator until the variation in time of said state variable exceeds a predetermined limit value.

16. The charging device of claim 15, wherein means are provided for switching off the charging current when the variation in time of the state variable exceeds the predefined limit value.

17. The charging device of claim 16, wherein means are provided for gradually reducing the charging current to zero when the variation in time of the state variable exceeds the predefined limit value.

18. A lithium accumulator comprising:

first means for connecting the accumulator to a charging device;

second means for monitoring the voltage on the accumulator during injection of said charging current;

third means for additionally monitoring a variation in time of at least one state variable characteristic of the accumulator;

wherein said third means are configured for generating a signal to said charging device to continue injection of the charging current into the accumulator until the variation in time of said state variable exceeds a predetermined limit value.

19. The lithium ion accumulator of claim 18, wherein at least one of said second and third means is arranged at least partially in said charging device.