Method for rapid charge control in lithium batteries
This invention includes a method for charging lithium-based batteries. Battery type is identified by a charger by way of a third terminal. For nickel-based cells, the third terminal is coupled to a thermistor for sensing temperature. For lithium-based cells, the third terminal is coupled to the rechargeable cell disposed within the battery pack. If a nickel cell is identified, the cell is charged by conventional means. If a lithium cell is identified, the charger applies a full current until any serial elements disposed between the battery pack terminals and the cell reach a high impedance state. The charger then reduces the charging current to a low level for a predetermined time. After this time has elapsed, the charger then reapplies a high current. If the voltage across the serial elements remains low, charging continues. However, if the voltage across the serial elements exceeds a predetermined threshold, the charger then decrements the current by a predetermined amount.
1. A method of charging a battery, the method comprising the steps of:
a. providing a battery having at least three terminals: a first terminal for receiving a charging current, a return terminal, and a third terminal coupled to a cathode of a rechargeable cell disposed within the battery;
b. applying a charging current having a first magnitude;
c. sensing a difference in voltage between the first terminal and the third terminal; and
d. reducing the charging current to a second magnitude when the difference in voltage between the first terminal and the third terminal exceeds a predetermined threshold.
2. The method of claim 1 , further comprising the step of holding the charging current at the second magnitude for a first predetermined time.
3. The method of claim 2 , further comprising the step of applying a charging current of the first magnitude for a second predetermined time after the first predetermined time has elapsed.
4. The method of claim 3 , further comprising the step of decrementing the current by a predetermined amount if the voltage between the first terminal and the third terminal exceeds the predetermined threshold during the second predetermined time.
5. The method of claim 4 , further comprising the step of actuating an annunciator when the current has been decremented to a predetermined current level.
6. The method of claim 5 , further comprising the step of terminating charging current when the voltage between the second and third terminals reaches a predetermined termination voltage.
7. The method of claim 6 , further comprising the step of applying a minimum current when the voltage between the second and third terminals is below a predetermined minimum voltage.