JP3190160B2 - Rechargeable battery capacity display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery capacity display device for calculating and displaying a remaining capacity from a charge / discharge current of a secondary battery.

[0002]

2. Description of the Related Art Hitherto, various types of capacity display devices for detecting and displaying the remaining capacity of a secondary battery have been known, one of which is described in JP-A-4-325834. In this capacity display device, a voltage generated at both ends of a low resistance inserted in a battery charging / discharging circuit is input to a microcontroller via an amplifier, and is converted into a digital value by an A / D converter. From the charge current detection circuit or the discharge current detection circuit, the charge current value or the discharge current value is obtained, and from the charge current value or the discharge current value, the remaining capacity of the secondary battery is obtained by the remaining capacity calculation circuit. The value is displayed on a display circuit.

[0003]

However, in the prior art, an amplifier for amplifying a voltage generated between both ends of a low resistance inserted in a charging / discharging circuit, and an A / A converter for converting an output signal of the amplifier into a digital value. There is a problem that a detection error of the charge / discharge current value is caused by the offset voltage of the / D converter, and an error is also caused in the remaining capacity obtained based on the error.

In order to reduce this error, (1) an offset adjustment circuit is provided, and the variable resistance of the offset adjustment circuit is adjusted for each battery pack so that the output of the amplifier becomes 0 when the charge / discharge current is 0. Conventionally, a method and (2) a method of using an IC-based operational amplifier or a chopper-type operational amplifier adjusted so as to reduce an offset voltage in a production process as the amplifier have been adopted.

[0005] However, the method (1) is not efficient because the adjustment must be performed for each battery pack.
The method (2) is not practical because the operational amplifier adjusted to reduce the offset voltage is expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an amplifier and an A / D converter can be used without complicated adjustment and use of an expensive operational amplifier having a small offset voltage. It is an object of the present invention to provide a secondary battery remaining capacity display device capable of reducing an error due to the offset voltage of the secondary battery.

[0007]

To solve the above problems BRIEF SUMMARY OF THE INVENTION remaining capacity display device for a secondary battery according to the present invention, first
A current detecting resistor connected in series with the secondary battery between a terminal and a second terminal; first amplifying means for amplifying a voltage generated in the current detecting resistor during charging; Second amplifying means for amplifying a voltage generated in the resistor;
A / D conversion means for converting output signals of the first amplification means and the second amplification means into digital values, first amplification means for amplifying a voltage generated in the current detection resistor during charging, Second amplifying means for amplifying a voltage generated in the current detecting resistor at the time of discharging, A / D converting means for converting output signals of the first amplifying means and the second amplifying means into digital values, The secondary battery is connected to the charger
An idle state detecting means for detecting that the secondary battery is in an idle state which is neither a charged state nor a discharged state connected to a load ; an output of the A / D conversion means; Remaining capacity calculating means for calculating the remaining capacity of the secondary battery from the output of the state detecting means; and digital signals corresponding to the output signals of the first and second amplifying means when the unused state detecting means detects the unused state. Values Ico and Ido are stored, and a value obtained by subtracting Ico from a digital value corresponding to the output signal of the first amplifying means at the time of charging is set as a value corresponding to the charging current;
A value obtained by subtracting Ido from a digital value corresponding to the output signal of the second amplifying means at the time of discharging is set as a value corresponding to the discharging current, and a value corresponding to the charging current and discharging current is used for the secondary battery. It is characterized by comprising remaining capacity calculating means for calculating the remaining capacity by calculation, and display means for displaying the remaining capacity calculated by the remaining capacity calculating means. The leaving state detecting means includes, for example, the second terminal
An impedance element connected between the third terminals;
At the time of charging, the third terminal is between the first and second terminals.
Is fixed to the first potential via the resistor inside the charger connected to the
At the time of discharging, the third terminal is connected to the first and second terminals.
The second power supply is connected via a load internal resistor connected between the
The secondary battery is connected to the charger
Connected state of charge and the secondary battery is connected to the load
The battery is left in any of the discharged states
A state is detected as a potential change of the third terminal.
It is constructed. Further, as the impedance element,
It is also possible to use a thermistor that also detects the temperature of the secondary battery.
No.

Further, according to the secondary battery capacity display device according to a more preferred aspect of the present invention, the remaining capacity calculating means includes an output of the first amplifying means when the idle state detecting means detects an idle state. A value Ico obtained by subtracting the current consumption of the capacitance display device from the digital value corresponding to the signal, and a value Ido obtained by adding the current consumption Icc of the capacitance display device to the digital value corresponding to the output signal of the second amplifying means. A value obtained by subtracting Ico from a digital value corresponding to the output signal of the first amplifying means at the time of charging is set as a value corresponding to the charging current, and corresponding to the output signal of the second amplifying means at the time of discharging. A value obtained by subtracting Ido from the digital value is defined as a value corresponding to the discharge current, and the remaining capacity of the secondary battery is obtained by calculation using the values corresponding to the charge current and the discharge current.

[0009]

In the secondary battery capacity display device according to the present invention, the digital value corresponding to the offset voltage of the amplifier and the A / D converter is stored in the A / D converter during charging and discharging. By subtracting from the output digital value, the error can be reduced. That is, digital values Ico and Ido obtained by A / D converting the outputs of the first and second amplifying means in a state where the battery is left are stored, and the output of the first amplifying means is A / D converted during charging. The value obtained by subtracting Ico from the digital value.
From the digital value obtained by A / D conversion of the output of
By calculating the remaining capacity as a value corresponding to the charging current or the discharging current using the value obtained by subtracting do, an error in calculating the remaining capacity due to the offset voltage is reduced.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of a battery pack provided with a secondary battery capacity display device according to the present invention.
This battery pack includes a microcontroller 1, a current detection resistor 2, first and second amplifiers 3, 4, a display circuit 5, a standing state detection circuit 6, and a secondary battery 7 (hereinafter simply referred to as a battery). The idle state detection circuit 6 is a circuit that detects that the battery 7 is in an idle state. In this example, the idle state detection circuit 6 includes a thermistor Th and also functions as a temperature detection circuit of the battery 7.

The microcontroller 1 is an A / D converter 1
1. It has a charge current detection circuit 12, a discharge current detection circuit 13, and a remaining capacity calculation circuit 14, and outputs the contents of the remaining capacity calculation circuit 14 to the display circuit 5.

The battery pack is configured to be detachable from a charger or a device to be used, such as a load. When terminals 8 to 10 are connected to the charger, a charging current flows to the battery 7 and terminals 8 to 1
When a load is connected to 0, a discharge current flows from the battery 7. Here, the terminals 8 and 9 are connected to a charging terminal of the charger or a power input terminal of the load, and the terminal 10 is connected to a terminal other than the charging terminal of the charger or a terminal other than the power input terminal of the load. Terminal 10
The thermistor Th constituting the idle state detection circuit 6 is connected to the potential V through the resistor Rc inside the charger during charging.
, And is connected to the terminal 8 via the resistor Rd inside the load during discharge.

Therefore, while the battery 7 is being charged or discharged, a potential is always generated at the terminal 10, but when neither the charged state nor the discharged state, that is, when the battery 7 is in the idle state, the terminal 1
Since the potential of 0 becomes 0, it is possible to determine whether or not the battery 7 is in an idle state by checking the potential of the terminal 10 with the remaining capacity calculation circuit 14.

The first and second amplifiers 3 and 4 are circuits for amplifying an inter-terminal voltage generated in the current detecting resistor 2 when the battery 7 is charged and discharged, respectively, and its output is A / D.
After being converted into a digital value by the converter 11, the digital value is input to the charging current detecting circuit 12 and the discharging current detecting circuit 13.

The charge current detection circuit 12 and the discharge current detection circuit 13 determine the charge current Ic and the discharge current Id of the battery 7 from the output digital value of the A / D converter 11 and output them to the remaining capacity calculation circuit 14. It is.

The remaining capacity calculation circuit 14 calculates the charge amount and the discharge amount of the battery 7 based on the values of the charge current Ic and the discharge current Id obtained by the charge current detection circuit 12 and the discharge current detection circuit 13, respectively. These are added to or subtracted from the remaining capacity value of the battery 7 already stored and output to the display circuit 5. The display circuit 5 includes an LED, an LCD, or the like, and displays the remaining capacity of the battery 7 calculated by the remaining capacity calculation circuit 14. Next, the operation of the capacitance display device of FIG. 1 will be described with reference to the flowchart of FIG.

When the microcontroller 1 starts operating, the offset voltage during charging (digital value corresponding to the output signal of the amplifier 3 during charging) Ico and the offset voltage during discharging (corresponding to the output signal of the amplifier 4 during discharging). Digital value) Ido and the remaining capacity C are set to 0 (step S1). Thereafter, when the time Δt has elapsed (step S
2 and YES), the outputs of the amplifiers 3 and 4 are sequentially taken into the A / D converter 11 and converted into digital values (step S3).

Next, if the output of the idle state detection circuit 6 is 0, that is, if the battery 7 is in an idle state (YE in step S4)
S), Ico = Ic, Ido = Id (step S5), and then store the self-discharge current IH from the remaining capacity value C.
, The remaining capacity value C is obtained by the following equation (1). C = C-IH × Δt (1)

If C ≧ 0 (N in step S7)
O), the remaining capacity value C is displayed on the display circuit 5 (step S9). If the idle state advances and the result of step S7 becomes YES, then C = 0 (step S8). Next, when the battery 7 is in the charged state (NO in step S4, YES in step S10), the remaining capacity value C is obtained by the following equation (2) (step S11). C = C + (Ic−Ico) × Δt (2)

The remaining capacity value C is compared with a predetermined value (for example, the rated capacity of the battery 7) Cn. When C ≦ Cn (NO in step S12), the remaining capacity value C is obtained by the equation (2). The remaining capacity value C is displayed on the display circuit 5 (step S9), and the process returns to step S2.

When charging proceeds and the remaining capacity value C increases, and eventually C> Cn (YES in step S12), C = C
n (step S13), and the value of C does not increase even if the subsequent charging is continued. Next, when the battery 7 is in the discharged state (NO in step S4, NO in step S10), the remaining capacity value C is obtained by the following equation (3) (step S1).
4). C = C− (Ic−Ico) × Δt (3)

If C ≧ 0 (N in step S7)
O), the remaining capacity value C is displayed on the display circuit 5 (step S9). If the discharge state advances and the result of step S7 is YES, then C = 0 (step S8).

As described above, in the present embodiment, the digital values Ico and Ido obtained by A / D converting the output signals of the amplifiers 3 and 4 when the battery 7 is not stored are stored, and the amplifier 3 is charged during charging.
A value obtained by subtracting Ico from a digital value obtained by A / D conversion of the output signal of the amplifier 4 and a value obtained by subtracting Ido from a digital value obtained by A / D conversion of the output signal of the amplifier 4 at the time of discharging are values corresponding to a charging current or a discharging current. By calculating the remaining capacity C, the error due to the offset voltage of the amplifiers 3 and 4 and the A / D converter 11 can be reduced, and the calculation of the remaining capacity value C can be performed accurately. The present invention is not limited to the above embodiments, but can be implemented with various modifications as follows.

(1) In the embodiment, Ic and Id when the battery is left unattended are read as Ico and Ido, but if the current consumption Icc of the capacity display device is known in advance, Ic-Icc, Ido
d + Icc may be read as Ico and Ido. In this way, the remaining capacity value C can be accurately calculated even when the consumption current Icc of the capacity display device cannot be ignored compared to the self-discharge current.

(2) In the embodiment, the idle state detection circuit 6 is constituted by the thermistor Th. However, it may be constituted by a mechanical switch, and the idle state is detected when Ic and Id are equal to or less than predetermined values. Such a configuration may be used. In addition, the present invention can be variously modified and implemented without departing from the gist.

[0027]

As described above, according to the capacitance display device of the present invention, even if the offset voltage of the amplifier or the A / D converter is large, the remaining value of the battery can be obtained by subtracting the offset value from the measured value. The calculation error of the capacity can be reduced.

That is, in the present invention, digital values obtained by A / D conversion of the output signals of the first and second amplifiers when the battery is left unattended, or values obtained by subtracting the current consumption Icc of the capacitance display device from these digital values. To Ico, Ido
A value obtained by subtracting Ico from a digital value obtained by A / D conversion of the output signal of the first amplifier during charging;
At the time of discharging, complicated adjustment is required by calculating the remaining capacity by setting the value obtained by subtracting Ido from the digital value obtained by A / D converting the output signal of the second amplifier as the value corresponding to the charging current or discharging discharge, respectively. Without using an expensive operational amplifier having a small offset voltage, the error due to the offset voltage of the first and second amplifiers and the A / D converter can be reduced, so that the remaining capacity can be accurately displayed. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a secondary battery capacity display device according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microcontroller 2 ... Current detection resistor 3 ... First amplifier 4 ... Second amplifier 5 ... Display circuit 6 ... Leaving state detection circuit 7 ... Secondary battery 11 ... A / D converter 12 ... Charging current detection circuit 13: discharge current detection circuit 14: remaining capacity calculation circuit

Continuation of the front page (56) References JP-A-4-42075 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 31/36

Claims (4)

(57) [Claims] 1. A current detecting resistor connected in series with a secondary battery between a first terminal and a second terminal, and first amplifying means for amplifying a voltage generated in the current detecting resistor during charging. Second amplification means for amplifying a voltage generated in the current detection resistor at the time of discharging; and A / D conversion means for converting output signals of the first and second amplification means into digital values. When the connected state of charge and said secondary battery in the charger
Leaving state detecting means for detecting that the secondary battery is in a leaving state other than any of the discharging states connected to the load; and the first and second amplification when the leaving state detecting means detects the leaving state Digital values Ico and Ido corresponding to the output signal of the first amplifying means are stored, and a value obtained by subtracting Ico from the digital value corresponding to the output signal of the first amplifying means at the time of charging is set as a value corresponding to the charging current. The value obtained by subtracting Ido from the digital value corresponding to the output signal of the second amplifier means as a value corresponding to the discharge current, and using the values corresponding to the charge current and the discharge current, the remaining capacity of the secondary battery And a display means for displaying the remaining capacity calculated by the remaining capacity calculation means. 2. A current detecting resistor connected in series with a secondary battery between a first terminal and a second terminal, and first amplifying means for amplifying a voltage generated in the current detecting resistor during charging. Second amplification means for amplifying a voltage generated in the current detection resistor at the time of discharging; and A / D conversion means for converting output signals of the first and second amplification means into digital values. When the connected state of charge and said secondary battery in the charger
Leaving state detecting means for detecting that the secondary battery is in a leaving state other than any of the discharging states connected to the load; and an output of the first amplifying means when the leaving state detecting means detects the leaving state A value Ico obtained by subtracting the current consumption of the capacitance display device from the digital value corresponding to the signal;
And a value Ido obtained by adding the current consumption Icc of the capacitance display device to the digital value corresponding to the output signal of the amplifying means, and subtracting Ico from the digital value corresponding to the output signal of the first amplifying means during charging. The value corresponding to the charging current,
A value obtained by subtracting Ido from a digital value corresponding to the output signal of the second amplifying means at the time of discharging is set as a value corresponding to the discharging current, and a value corresponding to the charging current and discharging current is used for the secondary battery. A capacity display device for a secondary battery, comprising: a remaining capacity calculating means for calculating a remaining capacity by calculation; and a display means for displaying the remaining capacity calculated by the remaining capacity calculating means. 3. The apparatus according to claim 2, wherein said idle state detecting means comprises a second terminal.
And an impedance element connected between the third terminal
During charging, the third terminal is connected to the first and second terminals.
The first constant current through a resistor inside the charger connected between
And the third terminal is connected to the first and second terminals during discharging.
Via the internal resistance of the load connected between
2 to charge the secondary battery
State of charge connected to the battery and the secondary battery
When the battery is left unattended, which is not one of the continuous discharge states
The left state is detected as a potential change of the third terminal.
The container according to claim 1 or 2, wherein:
Quantity display. 4. The secondary battery according to claim 2, wherein the impedance element is
Uses a thermistor that also detects battery temperature
4. The secondary battery capacity display device according to claim 3, wherein: