Battery pack for cordless power tools
A battery pack which includes a battery pack electronic control circuit adapted to control an attached power tool and/or an attached charger. The battery pack includes additional protection circuits, methodologies and devices to protect against fault conditions within the pack, as the pack is operatively attached to and providing power to the power tool, and/or as they pack is operatively attached to and being charged by the charger.
1. An electronics module of a battery pack for powering a cordless power tool, the pack including a plurality of lithium-ion battery cells therein, the module comprising:
an integrated circuit which includes a first voltage monitoring unit for monitoring individual lithium-ion cell voltages and total stack voltage of the lithium cells during charge and discharge operations;
a microcontroller external to and in connection with the integrated circuit;
a discharge FET for controlling one of current and power output from the battery pack to control a motor of the tool, wherein the microcontroller selectively controls the discharge FET so as to control current to the tool motor;
a second voltage monitoring circuit distinct from the first voltage monitoring unit that monitors individual cell voltages and, without interfacing with the battery electronic control unit, generates a disable signal in a charge operably coupled to the battery pack when any cell reaches an over-voltage condition during a charging operation; and
a fuse in a charge return line to the module.
2. The claim module of claim 1 wherein
the microcontroller provides pulse width modulation (PWM) control of the discharge FET so as to control tool motor current, and
the integrated circuit includes current limit processing circuitry for evaluating pack current during each switching period of the discharge FET and potentially limiting power out of the pack based on the evaluation.
3. The module of claim 1 , wherein
the current limit processing circuitry sets a reference voltage level representative of a current limit for the pack, and during each switching period of the discharge FET, compares a shunt voltage representing measured instantaneous pack current to the reference voltage level, and
if shunt voltage qual or exceeds the reference voltage level in a given switching period, the current limiting processing circuitry generates an output signal to the microcontroller to turn off the discharge FET for the remainder of the switching period to reduce power out of the pack.
4. The module of claim 1 , wherein
the microcontroller provides pulse width modulation (PWM) control of the discharge FET so as to control motor current, and
the integrated circuit further includes average current limit processing circuitry for feeding back average current information to the microcontroller so as to PWM control the discharge FET.
5. The module of claim 1 wherein the second voltage monitoring circuit includes a fuse in a serial data path connecting the second voltage monitoring circuit to a disable circuit in the charger, wherein the fuse creates an open circuit in the data path when any cell reaches an over-voltage condition during a charging operation.
6. The module of claim 1 wherein the disable circuit includes a transistor having a control terminal connected to the data path and operable to generate the disable signal when the data path having an open circuit.
7. A secondary circuit for providing over-voltage protection for battery cells in a battery pack, the battery pack having a first voltage monitoring circuit that monitors individual cell voltages of battery cells residing in the battery pack, the secondary circuit comprising:
a secondary voltage monitoring circuit in the battery pack, distinct from the first voltage monitoring circuit, that monitors individual cell voltages and sends a disable signal to a battery charger operably coupled to the battery pack upon detecting any cell reaching an over-voltage condition; and
a second circuit in the battery charger configured to receive the disable signal and interrupt charge current from the charger in response to the disable signal.
8. The secondary circuit of claim 7 further comprises a fuse in a serial data path connecting the second voltage monitoring circuit to a disable circuit in the charger, wherein the fuse creates an open circuit in the data path when any cell reaches an over-voltage condition during a charging operation.
9. The secondary circuit of claim 8 wherein the disable circuit includes a transistor having a control terminal connected to the data path and operable to generate the disable signal when the data path having an open circuit.
10. The secondary circuit of claim 7 wherein the first voltage monitoring circuit resides in one of the battery pack or the battery charger.
11. A cordless power tool system having a battery pack that operably couples to a battery charger, the system includes a first voltage monitoring unit that monitors individual cell voltages of battery cells residing in the battery pack and a charge control unit that controls delivery of a charge current to the battery pack during charging, the battery pack comprising:
a housing;
a plurality of battery cells within the housing; and
a secondary voltage monitoring circuit separate from the first monitoring unit that monitors the plurality of battery cells individually to detect when any cell reaches an over-voltage condition and provides a disable signal to the battery charger upon detecting a battery cell having an over-voltage condition, wherein the battery charger interrupts the charge current in response to receiving the disable signal.
12. The power tool system of claim 1 , wherein the first voltage monitoring unit provides a signal representing a measured individual cell voltage to the charge control unit during charging, and the charge control unit controls balancing of cell voltages during a charge based on signals received from the first voltage monitoring unit.
13. The power tool system of claim 11 , further comprising:
a fuse in a charge return line within the battery pack acting as additional protection in a case where the charge control unit becomes inoperative and current exceeds normal levels during charging.
14. The power tool system of claim 11 wherein the charge control unit resides in the battery pack.
15. The power tool system of claim 11 wherein the charge control unit resides in the battery charger.
16. The secondary circuit of claim 11 wherein the first voltage monitoring circuit resides in one of the battery pack or the battery charger.
17. The power tool system of claim 11 wherein the second voltage monitoring circuit includes a fuse in a serial data path connecting the second voltage monitoring circuit to a disable circuit in the charger, wherein the fuse creates an open circuit in the data path when any cell reaches an over-voltage condition during a charging operation.
18. The power tool system of claim 17 wherein the disable circuit includes a transistor having a control terminal connected to the data path and operable to generate the disable signal when the data path having an open circuit.