JPH06109819A - Residual capacity display device of battery - Google Patents

Abstract

PURPOSE:To correct the fluctuations of the discharge efficiency of a battery corresponding to the magnitude of a discharge current value by simple constitution. CONSTITUTION:The discharge current of a battery 1 is detected by a current detection resistor 2, a discharge current amplifying circuit 6 and an A/D converter circuit 8. The time integrated value of the detected discharge current is subtracted by a residual capacity operation circuit 9 to calculate the residual capacity of the battery 1 and the residual capacity is displayed on a display circuit 10. Herein, the current detection resistor 2 is constituted of a resistor having a temp. characteristic correcting the variation of the discharge efficiency of the battery 1 corresponding to the magnitude of the discharge current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for displaying the remaining capacity of a chargeable / dischargeable battery such as a Ni-Cd battery.

[0002]

2. Description of the Related Art A chargeable / dischargeable battery is used by being mounted on a portable battery-applied device or the like, removed from the device every time the battery capacity runs out, charged by a charger, and then re-installed on the device. By repeating the above-mentioned work, it can be used many times.

It is known that the remaining capacity of the battery is calculated and displayed in order to prompt the user to charge the battery. The remaining capacity of the battery is calculated by detecting the discharge current value with a resistance for current detection or the like and sequentially subtracting the discharge current amount per unit time from the initial capacity of the battery using a microcomputer or the like.

FIG. 5 is a diagram showing discharge efficiency characteristics of a battery when continuously discharged at a constant current. As shown in FIG. 5, the capacity of a battery generally decreases as the discharge current value increases.

FIG. 6 (b) is an explanatory view showing an intermittent discharge in which a current value of 20 (A) is discharged for 10 seconds and rested for T seconds. FIG. 6 (a) is as shown in FIG. 6 (b). It is a figure which shows the discharge efficiency characteristic with respect to the rest time at the time of performing intermittent discharge.
As shown in FIG. 6 (a), if the downtime T is shortened, the efficiency is lowered. It is considered that this is because when the temperature inside the battery rises due to discharge, the loss increases due to heat generation of the internal resistance of the battery.

Usually, in the remaining capacity display of the battery, there are many cases in which a display prompting the charging is displayed when the remaining capacity becomes 20% or less.

[0007] Here, when the fluctuation of the discharge efficiency due to the magnitude of the discharge current is not corrected, the remaining capacity becomes 20% as the current value increases, and when the display prompting the charging is made, it can be actually used. The problem is that the capacity is decreasing.

For example, as shown in FIG.
The discharge capacity of the battery when continuously discharged in (A) is 10
If (A) is 100%, it is about 90%. Therefore, when the fluctuation of the discharge efficiency is not corrected, the available capacity is about 10% of the initial capacity when the remaining capacity is calculated to be 20% and a reminder display for charging is displayed.

Therefore, conventionally, when a discharge current amount per unit time is sequentially subtracted in a microcomputer or the like, a method of correcting the variation of the discharge characteristic by changing the subtraction amount according to the discharge current value is performed. There is.

[0010]

However, when the fluctuation range of the discharge current is large depending on the size of the load and is often used intermittently, such as an electric power tool, a large fluctuation of the current value or work is required. Corresponding to the complicated change of the interval,
If a change in discharge efficiency is to be corrected each time, a large memory is required for the microcomputer.

A method of directly detecting and correcting the battery temperature is also conceivable. However, since a circuit for detecting the battery temperature is additionally required, the number of parts constituting the entire circuit increases and the cost also increases. There is a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a battery remaining capacity display device capable of correcting a variation in discharge efficiency with a simple structure.

[0013]

In order to achieve the above object, the present invention detects the discharge current of a battery by a current detection means and subtracts the time integrated value of the detected discharge current to subtract the remaining capacity of the battery. In the battery remaining capacity display device for displaying the calculated remaining capacity, the current detection means is a resistor having a temperature characteristic for correcting the fluctuation of the discharge efficiency of the battery according to the magnitude of the discharge current value. It is composed of.

[0014]

According to the present invention, when the discharge current value increases, the discharge efficiency of the battery decreases and the usable capacity decreases. At this time, due to the temperature characteristic of the resistor, the detected value of the discharge current increases above the current value, so the amount of subtraction per unit time increases, and the remaining capacity is sequentially subtracted to a larger extent,
The ratio of the remaining capacity to the initial capacity is calculated more accurately,
The decrease in discharge efficiency will be corrected.

[0015]

1 is a circuit block diagram showing a battery remaining capacity display device according to the present invention. The positive electrode B1 of the battery pack P,
The battery 1 and the current detection resistor 2 are connected in series between the negative electrodes B2.

The current detecting resistor 2 is composed of a nickel plate, which will be described later, and converts a discharging current from the battery 1 or a charging current flowing into the battery 1 into a voltage.

The charging current amplification circuit 5 amplifies a positive voltage generated in the current detection resistor 2 by the charging current.
The discharge current amplification circuit 6 uses the discharge current to detect the current detection resistor 2
It amplifies the negative voltage generated at. The AD conversion circuits 7 and 8 convert the output voltage from the charge / discharge current amplifier circuits 5 and 6 into digital values.

The remaining capacity calculation circuit 9 is composed of a microcomputer or the like and calculates the remaining capacity of the battery 1.
When there is an input from the D conversion circuit 7, the charging current amount is added to the present remaining capacity, and when there is an input from the AD conversion circuit 8, the discharging current amount is subtracted from the present remaining capacity.

The display circuit 10 is composed of an LED, an LCD or the like, and displays the remaining capacity of the battery 1 in, for example, five stages according to the output signal from the remaining capacity calculation circuit 9. When it is less than 1/5 of the capacity, 20% is displayed and a red LED is lit to prompt charging, and 1
/ 5 or more and less than 2/5 40%, 2/5 or more and less than 3/5 60% and 3/5 or more and less than 4/5 80
%, When it is 4/5 or more, 100% is displayed.

The constant voltage circuit 4 generates a required constant voltage and supplies power to the above circuits.

FIG. 2 is a characteristic diagram showing the temperature characteristic of the resistance of the nickel plate used for the current detection resistor 2 of this apparatus. FIG. 3 is a characteristic diagram showing a current characteristic of resistance of a nickel plate.
Generally, when the resistance value at temperature T ₁ (° C.) is R ₁ (Ω) and the resistance value at temperature T ₂ (° C.) is R ₂ (Ω), R ₂ = R ₁ {1 + α (T ₂ -T ₁ )} (1)

[0022] Here, α (% / ℃) intended to show the rate of a temperature coefficient of resistance at a temperature _{T 1 (℃), T 1} (℃) change in resistance to a temperature change of 1 ℃ based on , For example, at a temperature T ₁ = 20 (° C.), manganin has α≈
0.00001 and α = 0.006 for nickel. Conventionally, manganin or the like has been used as the current detection resistor 2 so as not to be affected by temperature changes.

Therefore, when the discharge current is 10 (A), the temperature T
₁ (° C.), resistance value R ₁₀ (Ω), temperature T ₁ + T (° C.) and resistance value R _I (Ω) at discharge current I (A),
The formula (1) becomes R _I = R ₁₀ [1 + α {(T ₁ + T) −T ₁ }] = R ₁₀ (1 + α · T) (2).

On the other hand, the amount W of heat generated by the resistance is W = R · I ² (3), so the temperature rise T of the resistance is approximately proportional to I ² .

Therefore, when the resistance value at a discharge current of 10 (A) is used as a reference, it can be replaced with α · T = K (I / 10) ² (4). However, K is a coefficient. Therefore,
From the equation (2), R _I = R ₁₀ {1 + K (I / 10) ² } (5)

Therefore, the gain of the discharge current amplifier circuit 6 is set to G
Then, the voltage V ₁₀ input to the remaining capacity calculation circuit 9 when the discharge current is 10 (A) is V ₁₀ = I · R · G = 10 · R ₁₀ · G (6) For example, the discharge current The same voltage V _{20 at} the time of 20 (A) becomes V ₂₀ = I · R · G = 20 · R ₂₀ · G (7). On the other hand, from the formula (5), R ₂₀ = R ₁₀ {1 + K (20/10) ² } = R ₁₀ (1 + 4K) (8) is obtained, and therefore the formula (7) is V ₂₀ = 20 · R ₁₀ (1 + 4K) · G (9)

[0027] Thus, the subtraction amount C _D20A when the discharge current 20 (A), the subtraction amount C _D10A when the discharge current 10 (A)
The ratio C _D20A / C _D10A to C _D20A / C _D10A = V ₂₀ / V ₁₀ = 20 · R ₁₀ (1 + 4K) · G / 10 · R ₁₀ · G = 2 (1 + 4K) = 2 (1 + 4 · 0.025 ) = 2.2. However, K = 0.025. The coefficient K can be set to a desired value by changing the thickness, length, shape, etc. of the nickel plate.

That is, assuming that a continuous discharge is performed at a discharge current of 20 (A), the remaining capacity is twice as fast as that at a discharge current of 10 (A) by using a conventional current detection resistor composed of manganin or the like. However, if the current detection resistor made of the nickel plate according to the present invention is used, the subtraction will be performed at a speed of 2.2 times, so that the discharge current 20
As compared with the case of (A), the subtraction will be 1.1 times faster.

Next, the procedure for displaying the remaining capacity will be described with reference to the flowchart of FIG. First, the remaining capacity C
Is reset to 0 (step S1). The following operation is performed every sampling time Δt (step S2).

First, the output voltage value ADC of the AD conversion circuit 7
Is taken in (step S3), and it is determined whether ADC = 0 (step S4). If ADC = 0, it means that charging is not in progress, and the process proceeds to step S7.

On the other hand, if ADC = 0 is not found in step S4, the charging current I is calculated by I = ADC / (R1 · G1) (step S5). However, R1 is the resistance value of the current detection resistor 2, and G1 is the gain of the charging current amplifier circuit 5.

Then, the remaining capacity is added by C = C + IΔt (step S6).

Next, it is determined whether or not the remaining capacity C is C <0 in the calculation (step S7). If C <0 is not satisfied, the process proceeds to step S9. On the other hand, if C <0, the C = 0 is reset. (Step S8).

Next, the output voltage value AD of the AD conversion circuit 8
D is taken in (step S9), and it is determined whether ADD = 0 (step S10). If ADD = 0, discharge is not in progress, so the process proceeds to step S13, while ADD = 0.
If not, the discharge current I is calculated by I = ADD / (R1 · G2) (step S11). However, G2 is the gain of the discharge current amplifier circuit 6.

Then, the remaining capacity is subtracted by C = C-IΔt (step S12).

Here, if the discharge current increases and the temperature of the current detection resistor 2 rises, the resistance value R1 thereof increases and the voltage value ADD taken in at step S9 also increases. Therefore, the calculated current value I in step S11 becomes larger than the actually increased discharge current value, and the subtraction amount in step S12 also becomes large.

Next, the remaining capacity C and the initial capacity C _MAX are compared (step S13). If C> C _MAX , the process proceeds to step S15. On the other hand, if C> C _MAX , C = C _MAX . (Step S14).

Then, if C <C _MAX ⅕ (YES in step S15), the remaining capacity of 20% is displayed, and the signal for urging charging is displayed (step S20).
Return to step S2. If C <C _MAX · 2/5 (YES in step S16), the remaining capacity of 40% is displayed (step S21), and the process returns to step S2. Also, C <
If C _MAX 3/5 (YES in step S17), the remaining capacity 60% is displayed (step S22), and step S2
Return to. If C <C _MAX · 4/5 (step S
If YES in step 18), the remaining capacity of 80% is displayed (step S2).
3) and returns to step S2.

On the other hand, if C <C _MAX · 4/5 is not satisfied (NO in step S18), the remaining capacity of 100% is displayed (step S19), and the process returns to step S2.

For example, in the case of continuous discharge at 20 (A),
Since the subtraction is performed at a speed 1.1 times faster than the case without correction, the display of the remaining capacity every 20% is 20 / 1.1 = 18.2 (%), so the actual capacity is 18.2%. It is displayed every time.

Then, the remaining capacity 20 for displaying a reminder of charging
The actual remaining capacity of the battery at the time of displaying% is 90-18.2 × 4 = 90-72.8 = 17.2 (%).

In this way, the rate of change in capacity when displaying every 20% from 100% of the battery capacity to empty can be made substantially equal.

In the case of intermittent discharge, the shorter the rest time is, the less time the battery temperature is lowered. Therefore, the temperature rise inside the battery is increased, the discharge efficiency is lowered, and the dischargeable capacity is also reduced.

On the other hand, as for the temperature of the current detecting resistor 2 formed of a nickel plate, the resistance value increases because the temperature increase increases as the rest time decreases, so that the capacitance when subtracting each sampling time is large. Become.

Therefore, the decrease in the dischargeable capacity of the battery due to the decrease in discharge efficiency is offset and corrected by the increase in the subtracted capacity due to the increase in the resistance value of the current detection resistor 2.

That is, if the increase in the internal resistance of the battery 1 due to the increase in the current and the increase in the resistance of the current detecting resistor 2 are almost equal, the loss due to the heat generation in the battery 1 causes the heat generation in the current detecting resistor 2. It can be corrected by increasing the resistance value due to.

Since the charging is usually performed with a constant current of 10 (A) or less, the variation in the resistance value of the current detection resistor 2 due to the use of the nickel plate does not pose a problem.

Also, the embodiment in which the battery remaining capacity display device is incorporated in the battery pack has been described, but the present invention is not limited to this.
It may be incorporated in a battery application device having a built-in load, a battery, a charging circuit and the like.

[0049]

As described above, according to the present invention, the current detecting means is composed of a resistor, and the temperature characteristic of the resistor is used to correct the discharge efficiency of the battery, which varies depending on the discharge current value. With the configuration, the remaining capacity can be displayed more accurately.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a battery remaining capacity display device according to the present invention.

FIG. 2 is a characteristic diagram showing temperature characteristics of resistance of a nickel plate.

FIG. 3 is a characteristic diagram showing current characteristics of resistance of a nickel plate.

FIG. 4 is a flowchart showing a procedure for displaying a remaining capacity.

FIG. 5 is a diagram showing discharge efficiency characteristics of a battery when continuously discharged at a constant current.

FIG. 6A is a diagram showing discharge efficiency characteristics with respect to rest time when intermittent discharge as shown in FIG.
FIG. 4 is an explanatory diagram showing an intermittent discharge in which a current value of 20 (A) is discharged for 10 seconds and then a rest for T seconds.

[Explanation of symbols]

 1 Battery 2 Current Detection Resistor 4 Constant Voltage Circuit 5 Charging Current Amplifier Circuit 6 Discharge Current Amplifier Circuit 7, 8 AD Conversion Circuit 9 Remaining Capacity Calculation Circuit 10 Display Circuit P Battery Pack

Claims (1)

[Claims] 1. A battery remaining capacity for detecting a discharge current of a battery by a current detecting means, subtracting a time integrated value of the detected discharge current to calculate a remaining capacity of the battery, and displaying the calculated remaining capacity. In the capacity display device, the current detection means is composed of a resistor having a temperature characteristic that corrects a variation in the discharge efficiency of the battery according to the magnitude of the discharge current value. .