JP2008283786A - Secondary battery charging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery charging system that prevents the secondary battery from being overdischarged state by monitoring a state of a secondary battery and performing shutdown and resetting of a control device when necessary. <P>SOLUTION: This secondary battery charging system comprises a cordless apparatus 30 having the secondary battery 34 and a charger 50, which is freely mountable to and detachable from the cordless apparatus 30, for charging the secondary battery 34. The cordless apparatus 30 comprises a voltage detection circuit 38, which detects a voltage of the secondary battery 34, a CPU 32, to which electric power can be supplied from the secondary battery 34 and the charger 50, and a control power supply switch 46, which is controlled by the CPU 32 to turn on and off the power supply from the secondary battery 34 to the CPU 32. The CPU 32 turns off the control power supply switch 46 to shut down the power supply from the secondary battery 34 to the CPU 32 when a voltage detected by the voltage detection circuit 38 is lower than a first predetermined voltage. The charger 50 supplies electric power to the CPU 32 when connected to the cordless apparatus 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a secondary battery charging system including a cordless device having a secondary battery and a charger.

  Secondary batteries are widely used in mobile devices such as mobile phones and notebook computers as power sources that can be charged and discharged. It is also attracting attention as a power source for cordless devices such as cordless cleaners, electric tools, and electric bicycles, and the field of use is expanding. Recently, a secondary battery pack in which a microcomputer (microcomputer) is mounted has been used. This microcomputer has a function of monitoring the state of the secondary battery and transmitting information to a tool, a charger or the like.

  In the case of a secondary battery pack equipped with a microcomputer, the power of the microcomputer is generally supplied from the secondary battery pack itself. Therefore, if the microcomputer continues to operate, the secondary battery pack may continue to consume electric capacity, leading to overdischarge. Various methods have been proposed to avoid this.

  For example, Patent Literature 1 describes a battery pack that reduces power consumption by shifting a microcomputer to a low power consumption mode when a device is not used. FIG. 3 is a diagram illustrating a configuration example of a circuit of the battery pack described in Patent Document 1. The secondary battery 11 in the battery pack 1 supplies electric power to the electric tool 2 that is a cordless device from the plus side charge / discharge terminal 12 and the minus side charge / discharge terminal 15. The current flowing through the power supply is measured by the current sensor 18. Further, the voltage of the secondary battery 11 is taken in and measured by the microcomputer 17 which is a calculation means through the voltage detection line 16. The microcomputer 17 receives the ON information of the operation switch 21 transmitted from the operation switch information communication unit 22 of the electric tool 2 at the operation switch information terminal 13. Further, when the remaining capacity of the secondary battery decreases to a specified value of the allowable lower limit, the microcomputer 17 requests the electric power tool 2 to stop discharging through the discharge stop request communication terminal 14. Thereafter, the load control device 24 of the power tool 2 receives the signal from the discharge stop request receiving terminal 25 and performs the stationary control of the motor 26.

  In the battery pack 1 and the electric tool 2 having the above-described configuration, when a trigger that is an operation switch of the electric tool 2 is accidentally entered by other surrounding tools or members during transportation or temporary storage, The operation switch information communication unit 22 transmits operation switch ON information to the battery pack 2 via the operation switch information terminal 23. In the battery pack 1, the microcomputer 17 receives the information from the operation switch information terminal 13 and recognizes that the power tool 2 is in an operating state. Further, the microcomputer 17 calculates the remaining capacity of the secondary battery 11 from at least one piece of information among the current measured by the current sensor 18 or the voltage of the secondary battery 11 measured via the voltage detection line 16.

  If the operation switch 21 of the electric tool 2 continues to be turned on, the remaining capacity of the secondary battery 11 decreases due to the power consumption of the motor 26 and reaches the discharge lower limit capacity. When the secondary battery 11 reaches the specified value of the discharge lower limit, the microcomputer 17 requests the electric power tool 2 to stop discharging via the discharge stop request communication terminal 14. In the electric tool 2, the load control device 24 stops the operation of the motor 26 within a predetermined time based on the discharge stop request received at the discharge stop request receiving terminal 25, and stops the discharge of the secondary battery 11.

  In a normal use state, the user recognizes that the remaining capacity of the secondary battery 11 has become equal to or lower than the discharge lower limit capacity because the motor 26 is stopped, and turns off the operation switch 21. However, when the operation switch 21 is erroneously turned ON, the operation switch 21 maintains the ON state even though the motor operation is stopped. In this case, the microcomputer 17 determines that the power tool 2 is operating and continues to operate. Therefore, the secondary battery 11 continues to be discharged with the power consumption by the microcomputer 17 even after the power consumption by the motor 26 is stopped, and the secondary battery 11 is overdischarged. Therefore, the microcomputer 17 in the battery pack 1 is not in a normal use state when the operation switch 21 is turned on even after the predetermined time has elapsed after the discharge stop request is transmitted, that is, the operation switch 21 is erroneously turned on. It is determined that it has been switched to the low power consumption mode.

Therefore, according to the battery pack 1, even when a trigger that is an operation switch of the electric tool 2 (cordless device) is accidentally turned on by other tools or members in the surroundings during transportation or temporary storage, Thus, overdischarge of the secondary battery 11 due to power consumption of the microcomputer 17 in the battery pack 1 can be prevented without increasing the cost such as adding hardware.
JP 2006-228862 A

  However, the microcomputer 17 in the battery pack 1 as described above consumes a small amount of power even when operating in the low power consumption mode. Therefore, the secondary battery 11 reaches an overdischarged state when left without being charged for a long time. Therefore, the secondary battery 11 may be in an overdischarge state when left after use or when the period from product shipment to first use is long.

  If the microcomputer 17 is turned off, the secondary battery 11 is charged and cannot know whether there is sufficient remaining capacity to turn on the microcomputer 17, so the microcomputer 17 is turned on again. There is a problem that can not be. Furthermore, if charging is performed while the microcomputer 17 is not operating, the secondary battery 11 may be in an overcharged state, so the microcomputer 17 needs to be operating even in the low power consumption mode. There is.

  The present invention solves the above-described problems of the prior art, and monitors the state of the secondary battery and shuts down and returns the control unit when necessary to prevent the secondary battery from being overdischarged. It is an object to provide a secondary battery charging system.

  In order to solve the above problems, a secondary battery charging system according to the present invention includes a cordless device having a secondary battery, and a cordless device that is detachable from the cordless device and charges the secondary battery. The cordless device is supplied with power from any one of the secondary battery and the charger, a voltage detection unit that detects the voltage of the secondary battery, and the secondary battery charging system. And a first switch that is controlled by the control unit and that turns on / off power supply from the secondary battery to the control unit, and the control unit is detected by the voltage detection unit. When the voltage is less than a first predetermined voltage value, the first switch is turned off to cut off power supply from the secondary battery to the control unit, and the charger is connected to the cordless device. The control unit And supplying the power.

  According to the first aspect of the present invention, the operation of the control unit can be stopped in a state where an overdischarge state is assumed, and the secondary battery can be prevented from being overdischarged. Can be restored.

  Hereinafter, embodiments of the secondary battery charging system of the present invention will be described in detail with reference to the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a secondary battery charging system according to a first embodiment of the present invention. First, the configuration of the present embodiment will be described. As shown in FIG. 1, the secondary battery charging system of the present embodiment includes a cordless device 30 having a secondary battery 34, and a charger 50 that is detachable from the cordless device 30 and charges the secondary battery 34. Have

  The cordless device 30 includes a CPU 32, a secondary battery 34, a device control unit 36, a voltage detection circuit 38, a DC / DC converter 40, a discharge control switch 42, a charge control switch 44, and a control power switch 46. In the present embodiment, it is assumed that the cordless device 30 is a cordless cleaner.

  The charger 50 includes an AC / DC converter 52, a DC / DC converter 54, and a charger charging switch 56. Although the secondary battery 34 can be charged by connecting the charger 50 to the cordless device 30, it is assumed that the charger 50 is not connected to the cordless device 30 in this embodiment.

  The CPU 32 corresponds to the control unit of the present invention, is connected to the secondary battery 34 via the DC / DC converter 40 and the control power switch 46, and supplies power from both the secondary battery 34 and the charger 50. Is possible.

  The device control unit 36 is connected to the secondary battery 34 via the discharge control switch 42 and operates an actual device. When the cordless device 30 is a cordless cleaner as in the present embodiment, the device control unit 36 is a motor control unit.

  The voltage detection circuit 38 corresponds to the voltage detection unit of the present invention, is connected to the secondary battery 34 and the CPU 32, and detects the voltage of the secondary battery 34.

  The DC / DC converter 40 converts the discharge voltage from the secondary battery 34 into a control power supply voltage and outputs it to the CPU 32 via the control power switch 46.

  The control power switch 46 corresponds to the first switch of the present invention and is controlled by the CPU 32 to turn on / off the power supply from the secondary battery 34 to the CPU 32. When the voltage detected by the voltage detection circuit 38 is less than the shutdown voltage value, the CPU 32 turns off the control power switch 46 to cut off the power supply from the secondary battery 34 to the CPU 32. Here, the shutdown voltage value corresponds to the first predetermined voltage value of the present invention, and is a voltage value that is considered highly likely to cause the secondary battery 34 to be over-discharged when the CPU 32 operates further.

  Further, the charger 50 supplies power to the CPU 32 when connected to the cordless device 30.

  The discharge control switch 42 corresponds to the fourth switch of the present invention, and is controlled by the CPU 32 to turn on / off the supply of power for operating the cordless device 30 performed from the secondary battery 34 to the device control unit 36. .

  When the voltage detected by the voltage detection circuit 38 is less than the overdischarge protection voltage value, the CPU 32 turns off the discharge control switch 42 and cuts off the supply of power for operating the cordless device 30. Here, the overdischarge protection voltage value corresponds to the third predetermined voltage value of the present invention, and is for the device control unit 36 that is performed to operate the cordless device 30 in order to protect the secondary battery 34 from overdischarge. This is a reference voltage value for shutting off the power supply, and is a value equal to or higher than the shutdown voltage value.

  The charge control switch 44 corresponds to the third switch of the present invention, and is controlled by the CPU 32 to turn on / off the power supply from the charger 50 to the secondary battery 34.

  The CPU 32 turns off the charging control switch 44 when the voltage detected by the voltage detection circuit 38 is equal to or higher than the overcharge protection voltage value, and the cordless device 30 is connected to the charger 50 and detected by the voltage detection circuit 38. When the detected voltage is less than the overcharge protection voltage value, the charge control switch 44 is turned on. Here, the overcharge protection voltage value corresponds to the second predetermined voltage value of the present invention, and is a voltage value that is considered highly likely to be overcharged when the secondary battery 34 is further charged. . Naturally, the overdischarge protection voltage value and the shutdown voltage value are values less than the overcharge protection voltage value.

  Note that the discharge control switch 42, the charge control switch 44, and the control power switch 46 are off when power is not supplied from the secondary battery 34 and the charger 50 to the CPU 32.

  Further, in the present embodiment, the charger 50 is not connected to the cordless device 30, but by connecting the charger 50 to the cordless device 30, each power line and signal line are connected. For example, by connecting the charging terminal 48 included in the cordless device 30 and the charging terminal 58 included in the charger 50, a charging current flows from the charger 50 to the secondary battery 34 inside the cordless device 30.

  The charger power switch 56 corresponds to the second switch of the present invention. When the charger 50 is connected to the cordless device 30, the charger 32 is controlled by the CPU 32 to turn on / off the power supply from the charger 50 to the secondary battery 34. When the charger 50 is not connected to the cordless device 30, it is off.

  The secondary battery charging system can also include a shutdown button (not shown) outside the cordless device 30. This shutdown button corresponds to the external input unit of the present invention, and turns on / off the control power switch 46 based on an external input by the operator.

  Next, the operation of the present embodiment configured as described above will be described. Basically, the CPU 32 monitors the voltage of the secondary battery 34 detected by the voltage detection circuit 38 and performs overcharge protection and overdischarge protection. Therefore, the CPU 32 turns off the charging control switch 44 when the cordless device 30 is not connected to the charger 50. Even when the cordless device 30 is connected to the charger 50, the CPU 32 turns off the charge control switch 44 when the voltage detected by the voltage detection circuit 38 is equal to or higher than the overcharge protection voltage value.

  In addition, when the voltage detected by the voltage detection circuit 38 is less than the overdischarge protection voltage value, the CPU 32 turns off the discharge control switch 42 to cut off the power supply to the device control unit 36 and the voltage detection circuit 38. When the detected voltage is less than the shutdown voltage value, the control power switch 46 is turned off to cut off the power supply to the CPU 32.

  First, consider a case where the remaining capacity of the secondary battery 34 is a sufficiently large value. In this case, since the voltage of the secondary battery 34 detected by the voltage detection circuit 38 is equal to or higher than the overdischarge protection voltage value, the CPU 32 controls the discharge control switch 42 and the control power switch 46 to be turned on. Therefore, the secondary battery 34 supplies power to the CPU 32 via the DC / DC converter 40 and the control power switch 46. At this time, the DC / DC converter 40 converts the discharge voltage (DC voltage) from the secondary battery 34 into a control power supply voltage (DC voltage). Since the charger 50 is not connected to the cordless device 30, the CPU 32 controls the charging control switch 44 to be turned off.

  In this state, the cordless cleaner operates when the operator turns on, for example, an external power switch (not shown). At that time, the secondary battery 34 supplies power to the device control unit 36 via the discharge control switch 42.

  When the power of the secondary battery 34 is gradually consumed and the remaining capacity of the secondary battery 34 decreases, the voltage of the secondary battery 34 decreases. When the voltage of the secondary battery 34 falls below the overdischarge protection voltage value, the CPU 32 turns off the discharge control switch 42 and cuts off the supply of power for operating the cordless device 30. In this state, the operator cannot operate the cordless cleaner unless the secondary battery 34 is charged. However, when the voltage of the secondary battery 34 is equal to or higher than the shutdown voltage value, the CPU 32 keeps the control power switch 46 on. Therefore, the power of the secondary battery 34 is continuously consumed by the CPU 32.

  Further, when the power of the secondary battery 34 is consumed, the remaining capacity of the secondary battery 34 decreases, and the voltage of the secondary battery 34 falls below the shutdown voltage value, the CPU 32 turns off the control power switch 46 and turns on the secondary battery. The power supply from the battery 34 to the CPU 32 is cut off. After that, unless the charger 50 is connected to the cordless device 30, the power of the secondary battery 34 is almost consumed (only a negligible amount). Therefore, this secondary battery charging system can prevent the secondary battery 34 from being overdischarged.

  Even when the voltage of the secondary battery 34 is not less than the shutdown voltage value, the operator can turn off the control power switch 46 by operating a shutdown button provided outside the cordless device 30. Thereby, when the inventory period from product shipment to the first use is long, the power consumption of the secondary battery 34 at the time of transportation can be suppressed.

  Further, the charger power switch 56 is off when the charger 50 is not connected to the cordless device. Therefore, even when AC input (AC input) is applied to the charger 50, when the charger 50 is not connected to the cordless device 30, the output of the charging terminal 58 is 0V, which improves safety. To do.

  As described above, according to the secondary battery charging system according to the first embodiment of the present invention, when the voltage of the secondary battery 34 becomes less than the overdischarge protection voltage value, the CPU 32 turns off the discharge control switch 42 to Since the power consumption of the secondary battery 34 is suppressed, the secondary battery 34 can be prevented from reaching an overdischarged state. Further, when the voltage of the secondary battery 34 becomes less than the shutdown voltage value, the CPU 32 turns off the control power switch 46 and stops the operation of the CPU 32. Therefore, the power of the secondary battery 34 is not consumed and the battery is left for a long time. Regardless, the secondary battery 34 can be prevented from reaching an overdischarged state.

  Further, when the charger 50 is connected to the cordless device 30, it supplies power to the CPU 32, so that the shut down CPU 32 can be easily restored. Therefore, the cordless cleaner can be supplied in a state where the CPU 32 is shut down until it is used in a general household, and even if the period from shipment to use by the consumer becomes long, the secondary battery 34 is excessive. It can prevent reaching a discharge state.

  Further, since an external input unit such as a shutdown button is provided, the CPU 32 can be forcibly shut down to a stopped state even in a state where overdischarge protection is not performed (a state where the voltage of the secondary battery 34 is equal to or higher than the shutdown voltage value). This can reduce power consumption during transportation.

  Furthermore, even when the charger 50 is AC-input, if the charger 50 is not connected to the cordless device 30, the output of the charging terminal 58 can be set to 0V, thus improving safety. To do.

  FIG. 2 is a block diagram showing the configuration of the secondary battery charging system according to the second embodiment of the present invention. The difference from the first embodiment is that the cordless device 30 is connected to the charger 50. The CPU 32 turns on the charger power switch 56 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is less than the overcharge protection voltage value. Further, as described above, the CPU 32 turns on the charge control switch 44 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is less than the overcharge protection voltage value. Therefore, the secondary battery 34 is charged by the electric power supplied from the charger 50.

  Further, the CPU 32 turns off the charger power switch 56 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is equal to or higher than the overcharge protection voltage value.

  Other configurations are the same as those of the first embodiment, and redundant description is omitted.

  Next, the operation of the present embodiment configured as described above will be described. First, it is assumed that the CPU 32 is in a shutdown state immediately before the charger 50 is connected to the cordless device 30. Therefore, since no power is supplied to the CPU 32 from either the secondary battery 34 or the charger 50, the discharge control switch 42, the charge control switch 44, and the control power switch 46 are off.

  When the cordless device 30 is connected to the charger 50, the charger 50 supplies power to the CPU 32. Specifically, the AC input power to the charger 50 is converted from an AC power source to a DC power source for charging by the AC / DC converter 52, converted to a control power source voltage by the DC / DC converter 54, and Input to the CPU 32.

  When power is input from the charger 50 to the CPU 32, the CPU 32 starts up. The CPU 32 turns on the charger power switch 56 and turns on the charging control switch 44 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is less than the overcharge protection voltage value. Let Therefore, the secondary battery 34 is charged by the electric power supplied from the charger 50.

  In addition, when the voltage detected by the voltage detection circuit 38 is equal to or higher than the shutdown voltage value when the CPU 32 is activated, the CPU 32 turns on the control power switch 46. If the voltage detected by the voltage detection circuit 38 is less than the shutdown voltage value when the CPU 32 is activated, the CPU 32 keeps the control power switch 46 turned off, and then the voltage detection circuit 38 detects the voltage. When the applied voltage becomes equal to or higher than the shutdown voltage value, the control power switch 46 is turned on.

  When the control power switch 46 is on, the secondary battery 34 supplies power to the CPU 32 via the DC / DC converter 40 and the control power switch 46.

  Even if the voltage detected by the voltage detection circuit 38 is less than the shutdown voltage value, if the charger power switch 56 and the charge control switch 44 are on, the CPU 32 turns on the control power switch 46. It may be configured.

  Further, when the voltage detected by the voltage detection circuit 38 is equal to or higher than the overdischarge protection voltage value, the CPU 32 turns on the discharge control switch 42. If the voltage detected by the voltage detection circuit 38 is less than the overdischarge protection voltage value, the CPU 32 keeps the discharge control switch 42 turned off, and then the voltage detected by the voltage detection circuit 38 is excessive. When the discharge protection voltage value is exceeded, the discharge control switch 42 is turned on. When the discharge control switch 42 is turned on, the operator can actually use the cordless cleaner by operating it.

  The CPU 32 may be configured to always turn off the discharge control switch 42 when the charger 50 is connected to the cordless device 30. That is, the cordless cleaner does not operate during charging. In that case, the operator can actually use the cordless cleaner by removing the charger 50 from the cordless device 30.

  During operation, the CPU 32 monitors the voltage of the secondary battery 34 using the voltage detection circuit 38. When the voltage is less than the overdischarge protection voltage value, the CPU 32 turns off the discharge control switch 42 to discharge the device control unit 36. Is stopped, and when it becomes less than the shutdown voltage value, the shutdown process is performed, and the control power switch 46 is turned off.

  In addition, when the secondary battery 34 is charged by the charger 50 and the voltage detected by the voltage detection circuit 38 is equal to or higher than the overcharge protection voltage value, the CPU 32 turns off the charge control switch 44. Further, the CPU 32 turns off the charger power switch 56 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is equal to or higher than the overcharge protection voltage value.

  Thereafter, the CPU 32 monitors the voltage of the secondary battery 34 using the voltage detection circuit 38 during operation, and the voltage detected by the voltage detection circuit 38 when the cordless device 30 is connected to the charger 50 is the overcharge protection voltage. When it becomes less than the value, the charging control switch 44 is turned on. Further, the CPU 32 turns on the charger power switch 56 when the cordless device 30 is connected to the charger 50 and the voltage detected by the voltage detection circuit 38 is less than the overcharge protection voltage value.

  When the power is not supplied to the CPU 32, the charge control switch 44 is turned off, and the secondary battery 34 is not charged. Further, when the cordless device 30 (cordless cleaner) is disconnected from the charger 50, the charger charging switch 56 is turned off. Therefore, the output of the charging terminal 58 shown in FIG.

  As described above, according to the secondary battery charging system according to the second embodiment of the present invention, when the CPU 32 is shut down, the discharge control switch 42 and the control power switch 46 are off and the CPU 32 is restored. In addition, the discharge control switch 42 and the control power switch 46 are turned on only when the voltage of the secondary battery 34 is equal to or higher than a predetermined voltage. Therefore, even when the charger 50 is connected to the cordless device 30 and the secondary battery 34 is charged, the secondary battery 34 is charged in a state protected from power consumption and prevents overdischarge. it can. Further, since the CPU 32 is automatically supplied with electric power from the charger 50 when the charger 50 is connected to the cordless device 30, a switch for returning from shutdown is not necessary.

  Further, even when the charger 50 is AC-input, when the charger 50 is not connected to the cordless device 30, such as when the cordless device 30 (cordless cleaner) is disconnected from the charger 50, etc. Since the output of the charging terminal 58 can be 0 V, safety is improved.

  Further, even when the charger 50 is connected to the cordless device 30 and the CPU 32 is activated, the CPU 32 charges only when the voltage detected by the voltage detection circuit 38 is less than the overcharge protection voltage value. Since the power supply switch 56 and the charging control switch 44 are turned on, the secondary battery 34 can be prevented from reaching an overcharged state.

  The secondary battery charging system according to the present invention can be used in a secondary battery charging system having a cordless device such as a cordless cleaner having a secondary battery and a charger detachably attached to the cordless device.

It is a block diagram which shows the structure of the secondary battery charging system of the form of Example 1 of this invention. It is a block diagram which shows the structure of the secondary battery charging system of the form of Example 2 of this invention. It is a block diagram which shows the structure of the conventional battery pack and electric tool.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery pack 2 Electric tool 11 Secondary battery 12 Positive side charge / discharge terminal 13 Operation switch information terminal 14 Discharge stop request | requirement communication terminal 15 Negative side charge / discharge terminal 16 Voltage detection line 17 Microcomputer 18 Current sensor 19 Temperature sensor 21 Operation switch 22 Operation Switch information communication unit 23 Operation switch information terminal 24 Load control device 25 Discharge stop request receiving terminal 26 Motor 30 Cordless device 32 CPU
34 Secondary Battery 36 Device Control Unit 38 Voltage Detection Circuit 40 DC / DC Converter 42 Discharge Control Switch 44 Charge Control Switch 46 Control Power Switch 48 Charging Terminal 50 Charger 52 AC / DC Converter 54 DC / DC Converter 56 Charging Charger switch 58 charging terminal

Claims (5)

A secondary battery charging system comprising: a cordless device having a secondary battery; and a charger that is detachable from the cordless device and charges the secondary battery,
The cordless device is
A voltage detector for detecting the voltage of the secondary battery;
A control unit capable of supplying power from both the secondary battery and the charger;
A first switch controlled by the control unit and configured to turn on / off power supply from the secondary battery to the control unit;
The controller turns off the first switch to cut off the power supply from the secondary battery to the controller when the voltage detected by the voltage detector is less than a first predetermined voltage value;
The secondary battery charging system according to claim 1, wherein the charger supplies power to the control unit when connected to the cordless device. The charger is
When the charger is connected to the cordless device, it is controlled by the control unit to turn on / off the power supply from the charger to the secondary battery, and the charger is connected to the cordless device. A second switch that is off if not,
When the cordless device is connected to the charger and the voltage detected by the voltage detection unit is less than a second predetermined voltage value that is greater than or equal to the first predetermined voltage value, the control unit The switch is turned on, and the second switch is turned off when the cordless device is connected to the charger and the voltage detected by the voltage detector is equal to or higher than the second predetermined voltage value. The secondary battery charging system according to claim 1. The cordless device includes a third switch that is controlled by the control unit and that turns on / off power supply from the charger to the secondary battery,
The control unit turns off the third switch when the voltage detected by the voltage detection unit is equal to or higher than the second predetermined voltage value, and the cordless device is connected to the charger and the voltage detection unit 3. The secondary battery charging system according to claim 2, wherein the third switch is turned on when the voltage detected by the step is less than the second predetermined voltage value. 4. The cordless device includes a fourth switch that is controlled by the control unit and that turns on / off power supply for operating the cordless device from the secondary battery,
When the voltage detected by the voltage detection unit is not less than a third predetermined voltage value that is not less than the first predetermined voltage value and less than the second predetermined voltage value, the control unit may The secondary battery charging system according to any one of claims 1 to 3, wherein a power supply for operating the cordless device is cut off by turning off a switch.   5. The secondary battery charging system according to claim 1, wherein the cordless device includes an external input unit that turns on and off the first switch based on an external input. 6.

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