Rechargeable battery module and battery charging method
An embodiment of the invention provides a rechargeable battery module including a battery bank having serial connected battery units, a charging transistor providing a charging current to the battery bank, a balancing circuit for detecting and balancing voltage values of battery units and battery bank and a control chip. When a first voltage value of a first battery unit reaches a charge-off voltage, the control chip estimates a first unbalanced voltage difference between the first voltage and the minimal voltage among battery units. The control chip disables the charging transistor and estimates a second unbalanced voltage difference between voltages of the first battery unit and the battery unit having a minimal voltage. The control chip enables the balancing circuit to balance the first battery unit. When the voltage of the first battery is dropped by a calibration target, the charging transistor is enabled.
1. A rechargeable battery module, comprising:
a battery bank having serial connected battery units;
a charging transistor providing a charging current to the battery bank;
a balance circuit coupled to the battery to detect and to balance voltage values of the battery units and the battery bank; and
a control chip receiving the voltage values of the battery bank and the battery units, when a first voltage value of a first battery unit among the battery units reaches a charge-off voltage value, the control chip estimating a first unbalanced voltage difference and then disabling the charging transistor to stop providing the charging current,
wherein when the charging transistor is disabled, the control chip estimates a second unbalanced voltage difference, and then enables the balance circuit to balance the voltage value of the first battery unit, and when the voltage value of the first battery unit is balanced for a calibration target, the control chip enables the charging transistor,
wherein the first unbalanced voltage difference is between the first voltage value and a first minimum voltage value among the voltage values of the battery units before the charging transistor is disabled, and wherein the second unbalanced voltage difference is between a second voltage value of the first battery unit and a second minimum voltage value among the voltage values of the battery units after the charging transistor is disabled, and the calibration target relates to the first unbalanced voltage difference and the second unbalanced voltage difference.
2. The module as claimed in claim 1 , wherein when the first unbalanced voltage difference exceeds a balance threshold, the control chip enables the balance circuit to balance the voltage value of the first battery unit.
3. The module as claimed in claim 1 , wherein the control chip calculates a voltage difference between the first unbalanced voltage difference and the second unbalanced voltage difference, and the calibration target is a sum of the second unbalanced voltage difference and a product of the voltage difference and a ratio, wherein the ratio is less than 1.
4. The module as claimed in claim 3 , wherein the ratio is 0.5.
5. The module as claimed in claim 1 , wherein when the charging transistor is enabled, the control chip determines whether a state of the battery bank meets a charging mode switch condition, and the battery bank is charged by a constant voltage charging mode when the state of the battery bank has met the charging mode switch condition.
6. The module as claimed in claim 5 , wherein when the voltage value of the battery bank is a fully charged voltage value, the control chip determines that the state of the battery bank meets the charging mode switch condition.
7. The module as claimed in claim 1 , wherein when a first voltage difference between the voltage value of the first battery unit and the voltage value of any battery unit of the battery bank is larger than a balance threshold, the control chip enables the balance circuit to adjust a first charging rate of the first battery unit to be less than a second charging rate of a second battery unit among the battery units, wherein the voltage value of the second battery unit is the minimum voltage value among voltage values of the battery units.
8. A battery charging method for a battery bank having serial connected battery units, comprising:
charging the battery bank with a charging current;
detecting voltage values of each battery unit;
when a first voltage value of a first battery unit among the battery units reaches a charge-off voltage value, estimating a first unbalanced voltage;
stopping providing the charging current;
estimating a second unbalanced voltage difference; and
balancing the voltage of the first battery unit and providing the charging current again when the voltage value of the first battery unit is balanced for a calibration target,
wherein the first unbalanced voltage difference is between the first voltage value and a first minimum voltage value among the voltage values of the battery units before the charging transistor is disabled, and wherein the second unbalanced voltage difference is between a second voltage value of the first battery unit and a second minimum voltage value among the voltage values of the battery units after the charging transistor is disabled, and the calibration target relates to the first unbalanced voltage difference and the second unbalanced voltage difference.
9. The method as claimed in claim 8 , wherein when the first unbalanced voltage difference exceeds a balance threshold, the step of balancing the voltage of the first battery unit is executed.
10. The method as claimed in claim 8 , further comprising:
estimating a voltage difference between the first unbalanced voltage difference and the second unbalanced voltage difference; and
multiplying the voltage difference by a ration, and then adding the second unbalanced voltage difference to generate the calibration target, wherein the ratio is less than 1.
11. The method as claimed in claim 10 , wherein the ratio is 0.5.
12. The method as claimed in claim 8 , further comprising:
determining whether a state of the battery bank meets a charging mode switch condition after providing the charging current again, and charging the battery bank by a constant voltage when the state of the battery bank meets the charging mode switch condition.
13. The method as claimed in claim 12 , wherein when a voltage value of the battery bank is a fully charged voltage value, the control chip determines that the state of the battery bank has met the charging mode switch condition.
14. The method as claimed in claim 8 , wherein when a first voltage difference between the voltage value of the first battery unit and the voltage value of any battery unit of the battery bank is larger than a balance threshold, the voltage of the first battery unit is balanced to adjust a first charging rate of the first battery unit to be less than a second charging rate of a second battery unit, and the voltage value of the second battery is the minimum voltage value among voltage values of the battery units of the battery bank.