Charging device

A charging device has a charging unit and a control unit. The charging unit charges a battery pack the battery pack being either a first type or a second type of battery pack. The first type of battery pack includes a single battery cell or a first plurality of battery cells connected in series. The second type of battery pack includes a single battery unit or a second plurality of battery units connected in series. Each battery unit includes at least two battery cells connected in parallel. The control unit controls the charging unit to control at least one of a charging current flowing through the battery pack and a charging voltage applied across the battery pack, depending on the battery pack to be charged.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2007-277042 filed Oct. 25, 2007. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a charging device for charging a secondary battery such as a lithium ion secondary battery.

BACKGROUND

In general, a cordless electric tool uses a secondary battery pack that is rechargeable with a charging device as a power supply. A lithium ion (Li-ion) battery cell is commonly used to form the secondary battery pack. A charging device for a Li-ion type battery pack generally charges the battery pack with a constant charging current and at a constant charging voltage. In particular, in order to avoid reverse charging for each battery cell, the charging device charges the battery pack with the constant charging current until the battery voltage reaches a predetermined value, and then charges at the constant charging voltage until the current passing through the battery pack reduces under a predetermined value due to full charging.

There are two types of battery pack to be charged by the charging device: a first type of battery pack and a second type of battery pack. The first type of battery pack is a 4S1P type of battery pack having a nominal voltage of 14.4 V, in which four battery cells are connected in series. The second type of battery pack is a 4S2P type of battery pack having a nominal voltage of 14.4 V, in which a pair of battery cells is connected in parallel and four pairs of parallel-connected battery cells are connected in series.

If one charging device selectively charges the above two different types of battery packs and flows the same amount of charging current through each battery pack, the amount of current passing through each cell of the 4S1P type is twice as much as the amount of current passing through each cell of the 4S2P type. This phenomenon may result in shortening the lifespan of the 4S1P type, compared with the lifespan of the 4S2P type.

The charging voltage also influences the lifespan of the battery pack. If each battery cell is charged at a lower charging voltage, the lifespan of the battery pack is expected to be extended.

Further, an amount of discharging current from each cell of the 4S1P type is generally more than an amount of discharging current from each cell of the 4S2P type. Even if each type of battery pack is charged at the same voltage, the lifespan of the 4S1P type is shorter than the lifespan of the 4S2P type because of an amount of discharging current per cell.

An object of the present invention is to provide a charging device which charges a battery pack with a proper current and at a proper voltage depending on the type of battery pack to avoid affecting the lifespan of the battery pack.

SUMMARY

The present invention provides a charging device having a charging unit and a control unit. The charging unit charges a battery pack the battery pack being either a first type or a second type of battery pack. The first type of battery pack includes a single battery cell or a first plurality of battery cells connected in series. The second type of battery pack includes a single battery unit or a second plurality of battery units connected in series. Each battery unit includes at least two battery cells connected in parallel. The control unit controls the charging unit to control at least one of a charging current flowing through the battery pack and a charging voltage applied across the battery pack, depending on the battery pack to be charged.

DETAILED DESCRIPTION

The next description will explain a charging device200according to an embodiment of the present invention, referring toFIGS. 1 and 2.FIG. 1shows a circuit diagram of the charging device200for charging a battery pack2with power supplied from an alternating-current power supply P.

The charging device200charges any one of different types of battery packs2. In this embodiment, the charging device200charges a first type of battery pack2and a second type of battery pack2, which has a different configuration of battery cells2a. In this embodiment, the configuration of battery cells2ameans the number of battery cells and a connection manner of the battery cells in the battery pack: series-connection or parallel-connection, how many cells are connected in series, and how many cells are connected in parallel. Each of the first and second types of battery cells2aincludes a single battery cell2aor a plurality of battery cells2aand has a positive terminal and a negative terminal. The battery cells2ais made from a lithium ion (Li-ion) secondary cell.

The first type of battery pack, as illustrated inFIGS. 1 and 2, includes a single battery cell2aor a plurality of battery cells2aconnected in series in a single row, so called, a 1P type of battery pack. One example is a 4S1P battery pack having a nominal voltage of 14.4 V. The 4S1P battery pack includes four battery cells2aconnected in series.

The second type of battery pack, as illustrated inFIG. 7, includes a single battery unit or a plurality of battery units connected in series in a single row, each battery unit including at least two battery cells2aconnected in parallel. The second type of battery pack is so called a 2P type of battery pack. One example is a 4S2P battery pack having has a nominal voltage of 14.4 V and having eight battery cells2a, in which two battery cells2aare connected in parallel to form one battery unit and four battery unit are connected in series. The second type of battery pack2may have more than two battery cells2aconnected in parallel in each battery unit. Described above, the second type of battery pack includes a plural-P type of battery pack (plural being an integer more than 1). For example, a 4S3P battery pack has twelve battery cells2ain which three battery cells2aare connected in parallel to form one battery unit and four battery units are connected in series.

The battery pack2further includes an identifier7and a thermosensor8. The identifier7represents a configuration of the battery cells2ain the battery pack2. In particular, the identifier7represents the number of battery cells2aand their connecting configuration such as series-connection and/or parallel connection in the battery pack2. The identifier7includes a battery identifying resistor7having a resistance value depending on the configuration of the battery cells2ain the battery pack2. For example, a 2S2P battery pack includes a resistor having a value of Ra. A 2S1P, 3S2P, 3S1P, 4S2P, 4S1P, 5S2P, and 5S1P battery pack includes a resistor having a resistance value of Rb, Rc, Rd, Re, Rf, Rg, and Rh, respectively.

The thermosensor8is a thermistor provided close to or on the battery cell2ato detect a temperature in the battery pack2.

The charging device1is provided with a current detection unit3, a charging control signal transmission unit4, a charging current signal transmission unit5, a rectification smoothing circuit6, a second battery type determination resistor9, a rectification smoothing circuit10, a switching circuit20, a rectification smoothing circuit30, a power supply40, a microcomputer50, a charging current control circuit60, a charging current setting unit70, a battery temperature detection unit80, a battery voltage detection unit90, a charging voltage control unit100, and a display unit130.

The current detection unit3is a resistor, and detects a voltage applied across the resistor in order to obtain a charging current flowing through the battery pack2.

The rectification smoothing circuit10includes a full-wave rectifier circuit11and a smoothing capacitor12. The full-wave rectifier circuit11rectifies the alternating-current supplied from the alternating-current power supply P, and the smoothing capacitor12smoothes the direct-current outputted from the full-wave rectifier circuit11.

The switching circuit20includes a high-frequency transformer21having a primary winding and a secondary winding, a MOSFET (switching element)22connected with the primary winding in series, and the PWM control IC (switching control IC)23.

A driving power for the PWM control IC23is supplied from the rectification smoothing circuit (direct current power source)6. The rectification smoothing circuit6includes a transformer6a, a rectifier diode6b, and a smoothing capacitor6c, and passes the power from the power supply40to the PWM control IC23. The PWM control IC23receives a charging voltage control signal and a charging current control signal through the charging current signal transmission unit5, which is a photocoupler, from the charging current control circuit60. The PWM control IC23receives a start signal and a stop signal for controlling start and stop of charging the battery pack2through the charging control signal transmission unit4, which is a photocoupler, from the microcomputer50. The PWM control IC23changes the drive pulse width applied to the gate of the MOSFET22in order to adjust an output voltage outputted to the rectification smoothing circuit30and a charging current passing through the battery pack2.

The rectification smoothing circuit30includes a diode31connected with the secondary winding of the transformer21, a smoothing capacitor32, and a discharging resistor33. The diode31rectifies the alternating-current supplied from the switching circuit20, and the smoothing capacitor32smoothes the direct-current outputted from the diode31.

The determination resistor9divides a reference voltage (stabilized direct voltage) Vcc together with the identifier7. The divided voltage is outputted as cell configuration information indicating the number of the battery cells2aand their configuration in the battery pack2.

The power supply40includes transformers41ato41c, a switching element42, a control element43, a rectifier diode44, a three-terminal regulator46, a smoothing capacitor45connected to an input terminal of the regulator46, a smoothing capacitor47connected to an output terminal of the regulator46, and the reset IC48, and supplies power to the microcomputer50and the rectification smoothing circuit6. The reset IC48outputs a reset signal to the microcomputer50through the reset port53when the commercial power source P supplies power to the charging device200.

The microcomputer50includes output ports51aand51b, an A/D input port52, and a reset port53. The microcomputer50further includes a central processing unit (CPU)51, a read-only-memory (ROM) for storing control programs for the CPU51and data associated with the types of battery packs2, a random-access memory (RAM) used for a working area for the CPU51and a temporary storage area for the data, and a timer. The cell configuration information outputted from the determination resistor9, the battery temperature information outputted from the battery temperature detection unit80, the battery voltage information outputted from the battery voltage detection unit90, and the voltage detected by the current detection unit3are inputted into the A/D port52. Accordingly, the microcomputer50determines the battery temperature and the battery voltage. The microcomputer50generates control signals to the power supply40and the charging current control circuit60, and outputs control signals to the charging control signal transmission unit4and the display unit130, and a charging state signal from the output port51a.

the microcomputer50determinates the configuration and the number of the series-connected cells of the battery pack2based on the cell configuration information, and outputs a charging voltage control signal corresponding to the number of the series-connected cells from the output port51bto the charging voltage control unit100. The microcomputer50outputs a charging current control signal based on the cell configuration information to the charging current setting unit70. The reset port53receives a reset signal from the reset IC48.

The charging current control circuit60includes an operational amplifier circuit having operational amplifiers (op-amps)61and65, input resistors62and64and feedback resistors63and66for the op-amps61and65, a diode68, and current limiting resistor67. An inverting terminal of the op-amp61is connected to the current detection unit3. A non-inverting terminal of the op-amp65is connected to the charging current setting unit70. An output terminal of the charging current control circuit60is connected to the PWM control IC23through the charging current signal transmission unit5. The charging current control circuit60outputs the current control signal based on both the charging current (the voltage) detected by the current detection unit3and the reference value outputted from the charging current setting unit70. An output terminal of the op-amp61is connected to the A/D converter52in order to monitor the charging current, so that the microcomputer50determines a reduction of the charging current when the battery pack2is fully charged.

The charging current setting unit70sets an amount of charging current passing through the battery pack2, depending on the type of the battery pack2. The charging current setting unit70includes resistors71and72connected in series between the reference voltage Vcc and a ground. The charging current setting unit70further includes a resistor73which may be connected with the resistor72in parallel. The reference voltage Vcc is divided by the resistors71and72, and the divided voltage is outputted as a reference value for setting the charging current. The resistor73is connected with the with the resistor72in parallel, depending on the type of the battery pack2, so that the charging current setting unit7changes the amount of charging current.

For example, if the microcomputer50controls that the resistor73is selected as being connected to the resistor72in parallel and the resistor71is connected with the parallel-connected resistors72and73, the microcomputer50sets a first charging current I1passing through the battery pack2. If the microcomputer50controls that only the resistor72is selected as being connected with the resistor71in series, the microcomputer50sets a second charging current I2passing through the battery pack2. In this case, the microcomputer50sets the amount of the first charging current less than the amount of the second charging current.

In the charging current control circuit60, the resistors62and63and the op-amp61invert and amplify the voltage across the current detection unit3. The op-amp65amplifies the difference between the output of the op-amp61and the setting voltage corresponding to the charging current value set by charging current setting unit70. The output of the charging current control circuit60is supplied to the PWM control IC23through the charging current signal transmission unit5to control the switching operation of the MOSFET22. In other words, the current detection unit3, the charging current control circuit60, the charging current signal transmission unit5, the switching circuit20, and the rectification smoothing circuit30adjust the actual charging current passing through the battery pack2to the charging current set by the charging current setting unit70.

The battery temperature detection unit80includes resistors81and82connected in series between the reference voltage Vcc and the ground (voltage divider circuit). The reference voltage Vcc is divided by the thermosensor8and the resistors81and82. The divided voltage representing a temperature change in the resistance of the thermosensor8is outputted as battery temperature information to an A/D convertor52of the microcomputer50.

The battery voltage detection unit90includes resistors91and92, and is connected with the positive terminal of the battery pack2. The battery voltage is divided by the resistors91and92, and the divided voltage is outputted as battery voltage information to the A/D convertor52of the microcomputer50.

The charging voltage control unit100controls the charging voltage applied to the battery pack2, and includes a shunt regulator122, a first resistance setting circuit R1, and a second resistance setting circuit R2. The shunt regulator122is a well-known type of shunt regulator and has an anode terminal a, a cathode terminal k, and a reference terminal r. The first resistance setting circuit R1and the second resistance setting circuit R2are connected to the reference terminal r of the shunt regulator122.FIG. 2shows an equivalent circuit of the shunt regulator122having an operational amplifier (voltage comparator) Op, a current path transistor Tr, and a reference voltage source Vref including as a zener diode.

The first resistance setting circuit R1is connected between the positive terminal of the battery pack2and the reference terminal (comparison input terminal) r of the shunt regulator122, and includes resistors101,102, and103. The second resistance setting circuit R2is connected between the negative terminal of the battery pack2and the reference terminal r of the shunt regulator122, and includes resistors107,108,109, and110. The cathode terminal k of the shunt regulator122is connected with a current limiting resistor120and a diode121which are connected in series. A series-connected phase compensation resistor104and capacitor105is connected between the reference terminal r and the cathode terminal k of the shunt regulator122.

Provided that the first combined resistance of the first resistance setting circuit R1is r1, the second combined resistance of the second resistance setting circuit R2is r2, and an internal reference voltage of the shunt regulator122is Vref, for example, 2.5V, the output charging voltage Vo adjusted by the shunt regulator122becomes approximately Vref*(1+r1/r2). Accordingly, a mode for the charging voltage Vo can be changed if a divided ratio r1/r2is changed.

In this embodiment, the mode for the charging voltage Vo is switched by changing the first combined resistance r1. If the first combined resistance r1is changed, at least two charging voltage modes: a first voltage charging mode in which the charging voltage is relatively higher, and a second charging voltage mode in which the charging voltage is lower than that of the first charging voltage mode are s selectable.

In order to switch the above charging voltage modes, the resistor102is connected to a switching element (p-channel MOSFET)106in series. The resistor102is electrically connected with the resistor101in parallel when the switching element106is turned on. With this structure, if the first charging voltage mode is selected to generate the charging voltage Vo, the switching element106is turned off, and only the resistor101is selected as the combined resistance r1. If the second charging voltage mode is selected, the switching element106is turned on, so that the resistor102is electrically connected with the resistor101in parallel to provide the combined resistance r1. In this embodiment, the first charging voltage mode is selected for the 2P type of battery pack, and the second charging voltage mode is selected for the 1P type of battery pack. For example, the charging voltage of 4.15 V/cell is set for the 2P type of battery pack in the first charging voltage mode, and the charging voltage of 4.10 V/cell is set for the 1P type of battery pack in the second charging voltage mode.

The second combined resistance r2is changed in order to adjust the charging voltage depending on the number of series-connected battery cells2aof the battery pack2to be charged. If the number of series-connected battery cells is plural and the total charging voltage applied across the battery pack2is set higher, the series-connected resistor108and switching element (n-channel MOSFET)111is connected with the resistor107in parallel. Similarly, the series-connected resistor109and switching element (n-channel MOSFET)112is connected with the resistor107in parallel. The series-connected resistor110and switching element (n-channel MOSFET)113is connected with the resistor107in parallel. The gates of the switching elements111,112, and113are connected to the output port51bthrough the resistors115,117, and119, respectively. The biasing resistors114,116, and118are connected between the corresponding gate of the switching elements111,112, and113and the ground, respectively.

Each of switching elements111,112, and113is selectively controlled by the control signal from the microcomputer50, depending on the number of series-connected battery cells2ain the battery pack2to be charged. In this embodiment, the number of series-connected battery cells2ameans the number of series-connected battery cells in the 1P type of battery pack, and the number of series-connected battery units in the plural-P type of battery pack.

When the microcomputer50determines that the number of series-connected battery cells are two, the microcomputer50does not output the charging voltage control signal from the output port51bto any of the gate terminals of the FETs111,112and113to turn on the FETs111,112and113. Thus, a voltage divided by a series resistance of the first combined resistance r1and the resistor107is inputted into the reference terminal r of the potentiometer103to set a charging voltage corresponding to the two cells connected in series.

When the microcomputer50determines that the number of series-connected battery cells are three, the microcomputer50outputs the charging voltage control signal from the output port51bto turn on the FET111, and then the combined resistance r2is provided with the parallel-connected resistors108and107. Thus, a voltage divided by the series resistance of first combined resistance r1and the parallel-connected resistance of the resistors107and108is inputted into the reference terminal r to set a charging voltage corresponding to the three cells connected in series.

When the microcomputer50determines that the number of series-connected battery cells are four, the microcomputer50outputs the charging voltage control signal from the output port51bto turn on the FET112, and the combined resistance r2is provided with the parallel-connected resistors109and107. Thus, a voltage divided by the series resistance of the first combined resistance r1and a parallel-connected resistance of the resistors107and109is inputted into the reference terminal r to set a charging voltage corresponding to the four cells connected in series.

When the microcomputer50determines that the number of series-connected battery cells are five, the microcomputer50outputs the charging voltage control signal from the output port51bto turn on the FET113, and the combined resistance r2is provided with the parallel-connected resistors110and107. Thus, a voltage divided by the series resistance of the first combined resistance r1and a parallel-connected resistance of the resistor107and110is inputted into the reference terminal r to set a charging voltage corresponding to the five cells.

If the battery pack2includes a single battery cell2aor at least two battery cells connected in parallel, the second resistance setting circuit R2may have the corresponding combined resistance r2by changing the resistance of the resistor107without operationally connecting any other resistors108,109, or110into the second resistance setting circuit R2.

The display unit130indicates the charging state of the battery pack2, and includes an LED131, resistors132and133. The LED131includes a green diode G and a red diode R. When the charging state signal outputted from the output port51ais inputted into the red diode R via the resistor132, the red diode R lights up with red color, and indicates that the battery pack2is prior to charging. When the charging state signal is inputted into the green diode G via the resistor133, the green diode G lights up with green color, and indicates that the charging battery pack2is completed. Furthermore, when the charging state signal are inputted into both the green diode G via the resistor133and the red diode R via the resistor132concurrently, the LED131lights up with orange color, and indicates that the battery pack2is in a process for charging. In this embodiment, the LED131lights up with the red color before charging, with the orange color during charging, and with the green color after charging.

The next description will be made for explaining charging the charging device200.FIG. 2shows a flowchart illustrating a control for charging the battery pack2.

Generally, the charging device200(the microcomputer50) charges the battery back2with a constant charging current until the battery voltage reaches a predetermined voltage, and at a constant charging voltage after the battery voltage has reached the predetermined voltage.

Before the battery pack2is attached to the charging device200, the microcomputer50outputs a high signal (the reference voltage Vcc) as the charging state signal from the output port51ato the LED131via the resistor132so that the LED121lights up with the red color (step200).

Next, the microcomputer50determines whether or not the battery pack2is attached to the charging device200in response to the input from the battery temperature detection unit80, the determination resistor9, and the battery voltage detection unit90(step201).

If the battery pack2is attached (step201: YES), the microcomputer50determines the configuration of cells based on the cell configuration information inputted by the determination resistor9(step202). First, the microcomputer50determines the number of battery cells2aconnected in series in the battery pack2, according to the resistance of the battery identifying resistor7in step202. The microcomputer50then sets a charging voltage corresponding to the configuration of the cells determined in step202(step203).

In this embodiment, the charging device200charges the Li-ion battery pack including the number of series-connected battery cells2awhich is any one of two, three, four, and five. In other words, if the number of series-connected battery cells2ais three, the switching elements111is turned on and the charging voltage for three battery cells connected in series in the battery pack2is set. If the number of series-connected battery cells2ais four, the switching elements112is turned on and the charging voltage for four battery cells connected in series in the battery pack2is set. If the number of series-connected battery cells2ais five, the switching elements113is turned on and the charging voltage for five battery cells connected in series in the battery pack2is set. If the number of series-connected battery cells2ais two, all the switching elements111,112, and113are turned off and the charging voltage for two battery cells connected in series in the battery pack2is set.

Next, in step204, the microcomputer50determines whether the battery pack2is a 1P type of battery pack2or a 2P type of battery pack2. If the microcomputer50determines that the battery pack2is the 1P type (step204: YES), the microcomputer50outputs a low signal from the output port51bto the charging current setting unit70to operationally and electrically connect the resistor73with the resistor72in parallel. The charging current I1is then set based on the divided voltage of the reference voltage Vcc with the combined resistance of the resistors71,72, and73(step205). And, the microcomputer50goes to step206. In step206, the microcomputer50turns on the switching element106to set a charging voltage for each battery cell to 4.10 V and goes to step209.

If the microcomputer50determines that the battery pack2is the 2P type (step204: NO), the microcomputer50does not output the low signal to the charging current setting unit70and the resistor73remains without being connected to the resistor72. The charging current I2is then set based on the divided voltage of the reference voltage Vcc with the combined resistance of the resistors71and72(step207). Accordingly, the amount of charging current I2passing through the 2P type of battery pack2can be set larger than the amount of the charging current I1passing through the 1P type. And, the microcomputer50goes to step208. In step208, the microcomputer50turns off the switching element106to set the charging voltage for each battery cell to 4.15 V, which is slightly higher than the charging voltage for each battery cell in the 1P type. The microcomputer50then goes to step209.

In step209, the microcomputer50outputs a low signal as the start signal from the output port51ato the photocoupler4to set the PWM control IC23in an operation state and start charging the battery pack2. In the start of the charging, as is generally known, the microcomputer50charges the battery pack2with a constant charging current. The microcomputer50outputs high signals as the charging state signal from the output port51ato the display unit130during charging so that the LED131lights up with the orange color, indicating that the battery pack2is in a charging process.

After the charging is started, the microcomputer50monitors the charging current based on the voltage inputted from the current detection unit3into the A/D port52in step209. As the charging goes, the battery voltage increases gradually. When the battery voltage has reached a predetermined value, the microcomputer50changes the charging method from the constant current charging to the constant voltage charging. When the battery pack2is charged at the constant charging voltage, the charging current reduces gradually.

The microcomputer50determines whether the charging current (the voltage) has reached a predetermined current (step210). If the charging current has reached the predetermined current (step210: YES), the microcomputer50determines that the battery2is fully charged and outputs a high signal as the stop signal from the output port51ato the photocoupler4to set the PWM control IC23in the stop state (step211). After stopping the charging, the microcomputer50outputs a high signal as the charging state signal from the output port51ato the display unit130, causing the LED131to light up with the green color, indicating that the charging the battery pack2is finished.

Then, the microcomputer50determines whether the battery pack2is detached from the charging device200(step212). If the battery pack2is detached from the charging device1(step212: YES), the processing returns to step200.

In the above embodiment, when the microcomputer50determines that the battery pack2is a 1P type, both of the charging current and the charging voltage are set less than those for a 2P type. Generally, the lifespan of the battery pack2depends on the charging voltage, and one battery cell in the battery pack2is usually charged at the charging voltage of 4.20 V. If the charging voltage per cell is set at 4.10 V less than 4.20V, the lifespan of the battery pack2tends to extend. Further, the allowable current of 1P type is a half of allowable current of the 2P type. Considering that the battery pack2is used for a cordless power tool which needs a large amount of current, the charging at the lower charging voltage can contribute to extending the lifespan of the battery pack2, in addition to the charging with the less amount of charging current.

Alternatively, the amount of charging current I1for the 1P type can be set equal to or approximated to amount of the charging current I2for the 2P type (I1≦I2). The charging voltage per cell in the 1P type can be equal to the charging voltage per cell in the 2P type.

FIGS. 4,5, and6shows other embodiments.FIG. 4shows another embodiment in which the charging current for the 2P type is set as 10.0 A, which is twice as much as the charging current for the 1P type, 5.0 A. Accordingly, the charging current passing through each cell in the 1P type is the same as the charging current passing through each cell in the 2P type, and the charging voltage across each cell in the 1P type is equal to the charging voltage across each cell in the 2P type. In this case, the 1P and 2P types of battery pack2can have the substantially same length of the lifespan.

FIG. 5shows further embodiment in which the charging current for the 2P type is set as 10.0 A, which is twice as much as the charging current for the 1P type, 5.0 A. Accordingly, the charging current passing through each cell in the 1P type is the same as the charging current passing through each cell in the 2P type. Further, the charging voltage to each cell in the 1P pack is set as 4.10 V, which is less than the charging voltage to each cell in the 2P pack, i.e., 4.15 V. In this case, the lifespan of the 1P pack can be extended, because the charging voltage to each cell in the 1P pack is less than the charging voltage to each cell in the 2P pack.

FIG. 6shows further embodiment in which the charging current passing through the 1P type is set equally to the charging current passing through the 2P type, i.e., 5.0 A, and the charging voltage to each cell in the 1P type is set to 4.10 V, which is lower than the charging voltage to each cell in the 2P type, i.e., 4.15 V. In this case, the charging current passing through each cell in the 2P type is reduced to 2.5 A, which is a half of the charging current passing through each cell in the 1P type, i.e., 5.0 A. Accordingly, the lifespan of the 2P type of battery pack2can be extended.

As described above, in the charging device200according to the present invention, the proper charging current and the charging voltage for the Li-ion battery pack2can be changed, depending on the configuration of battery cells2ain the battery pack2. Accordingly, the charging device200can charge the battery pack2without affecting the length of lifespan and/or charging cycles of the battery pack2. Additionally, the number of charging cycles for each type of battery pack can be increased.

In the above embodiment, the charging device200charges the 1P and 2P types. However, the charging device200can be applied for charging the plural-P type of battery pack (plural being equal to or more than 3).

While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. In the above embodiment, the battery pack2is made from the Li-ion secondary cells. The present invention is applicable for charging nickel-cadmium battery pack and nickel-hydride battery pack. The charging device is used for only constant-current charging method. Any mechanical or electrical identifying mechanism for identifying the configuration of the battery pack2can be used as the identifier7in addition to the battery identifying resistor7. For example, the battery pack2may have a projection corresponding to a configuration of battery cells2ain the battery pack2. The charging device200has a detector for detecting the projection of the battery pack2. If the 1P type of battery pack2is attached, an elastic projection formed in the battery pack accommodating portion in the charging device is retracted so that the charging device200detects that the 1P type of battery pack is attached. If the 2P type if battery pack2is attached, the elastic projection maintains projecting so that the charging device200detects that the 2P type of battery pack2is attached.