JPH07953Y2 - Low battery detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a low battery detection device.

(Prior Art) Conventionally, for example, when detecting a low battery of a NiCad battery, the voltage value of the battery has been detected. Fig. 3 (a)
Shows the discharge characteristics of the nickel-cadmium battery at a constant current, and the vertical axis and the horizontal axis show the battery voltage and time, respectively. The solid line α and the dotted line β in the figure have been fully charged (hereinafter referred to as “full charge”) to the full charge capacity of the nickel cadmium battery (hereinafter referred to as “battery α”), and only charged for a short time until full charge (Hereinafter referred to as "short-time charging")
The discharge characteristics of a nicad battery (hereinafter referred to as "battery β") are shown. In the batteries α and β, a low battery is detected when the battery voltage reaches a predetermined voltage value (a volt).

However, when comparing the difference between the times b and c required for each battery to change from the voltage value a to the voltage value 0 volt in the figure, the time b is shorter than the time c. It can be said that it is smaller than that of the battery α.

That is, in such a method for detecting a low battery of a battery, when a low battery is detected for a battery having a different charge state, a difference may occur in the remaining amount at the time of detection.

(Problems to be Solved by the Invention) As described above, the conventional low battery detection device has a problem that the remaining amount of the battery at the time of detection of the low battery may differ when the charging state of the battery is different. It was

The present invention has been made in view of such a problem, and an object thereof is to provide a low battery in which the remaining amount of the battery at the time of detecting the low battery is substantially constant even when the state of charge of the battery is different. It is to provide a detection device.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above-mentioned object, a first invention is a voltage value detecting means for detecting a voltage value of a battery, and the voltage value is a first predetermined value or less. Determining means, a voltage differential value calculating means for calculating an absolute value of a time differential value of the voltage value, and a change amount calculating means for calculating a current value change amount of the battery at a predetermined time ΔT. And a low battery state of the battery when the voltage value is equal to or lower than a first predetermined value and the absolute value of the voltage differential value is equal to or higher than a second predetermined value set according to the current value change amount. It is characterized by comprising a detecting means for detecting.

A second invention is a voltage value detecting means for detecting a voltage value of a battery, a judging means for judging whether the voltage value is a first predetermined value or less, and a time differential value of the voltage value. A voltage differential value calculating means for calculating an absolute value of the battery, a change amount calculating means for calculating a current value change amount of the battery in a predetermined time ΔT, the voltage value being equal to or less than a first predetermined value, and the current change amount being Detection means for detecting a low battery state of the battery when the absolute value of the voltage differential value is equal to or more than a second predetermined value and is equal to or more than a third predetermined value set in accordance with the current value change amount. It is characterized by having.

(Operation) In the first invention, the voltage value of the battery is equal to or less than the first predetermined value,
The low battery state of the battery is detected when the absolute value of the time differential value of the voltage value is equal to or greater than the second predetermined value set according to the amount of change in the current value of the battery during the predetermined time ΔT. Therefore, according to the present invention, the time required for the voltage to reach 0 V from the time when the low barrier is detected can be made substantially constant regardless of the state of charge of the battery. In addition, the present invention variably sets the second predetermined value that is compared with the voltage change amount according to the current value change amount of the battery in the predetermined time ΔT, so that in a device in which the load changes and the current value changes. Can prevent false detection.

In the second invention, the voltage value of the battery is less than or equal to the first predetermined value,
A low battery of the battery when the amount of change in current of the battery in a predetermined time ΔT is less than or equal to a second predetermined value and the absolute value of the voltage differential value is less than or equal to a third predetermined value set according to the amount of change in current value. Detect the condition. According to the present invention, by adding the case where the amount of battery change is equal to or less than the second predetermined value to one condition for the determination of the low battery state, the erroneous detection of the low battery state can be further detected even if the current consumption of the load fluctuates. It can be surely prevented.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a low battery detection device according to an embodiment of the present invention. This low battery detection device detects a low battery of a nickel-cadmium battery 1 as a power source, and a resistor 2, Analog-digital converter (A / D converter) 3, microcomputer 4,
It consists of a display unit 5.

The resistor 2 is connected in series to the nickel-cadmium battery 1, and a voltage is generated across the resistor 2 according to the current from the nickel-cadmium battery 1. The A / D converter 3 converts the current sent from the NiCd battery 1 and the voltage generated in the resistor 2 into a digital signal. The microcomputer 4 calculates the time differential value of the voltage of the nickel-cadmium battery 1 to detect the low battery, and displays the indicator 5
Send a signal to. The display 5 displays low battery when a signal is sent from the microcomputer 4.

FIG. 3 (a) shows the discharge characteristics of the nickel-cadmium battery 1 at a constant current, and FIG. 3 (b) shows the relationship with the time differential time of the voltage. The solid line γ and the dotted line δ in the figure show the time differentiation of the battery α and the battery β, respectively. When the load current of the nickel-cadmium battery 1 varies, the variation of the load current of the nickel-cadmium battery 1 is shown in FIG. 3 (c), and the variation of the battery voltage is shown in FIG. 3 (d).
Fig. 3 (e) shows the variation of the time derivative of the battery voltage.

Next, the operation of this embodiment will be described based on the flowchart of FIG. 2 and FIG.

Current value A of NiCd battery 1 and voltage value V generated in resistor 2
Is converted to a digital signal by the A / D converter 3,
The voltage value and the current value are measured by the microcomputer 4 (step 201), and it is determined whether or not “V ≦ V0 (predetermined voltage value)” (step 202).

Step 202 prevents detection of a low battery unless the voltage value becomes V0, that is, the time differential value becomes equal to or less than a reference value e described later even if the battery voltage value does not become V0. Therefore, it is possible to prevent the low battery from being erroneously detected in that case. For example, it is effective against a sudden voltage drop (portion (a) in FIG. 3 (d)) that tends to occur immediately after the start of battery discharge.

If “V ≦ V0” is not satisfied in step 202, the process returns to step 201. If “V ≦ V0”, the time differential value (dV / dt = M1) of the voltage value at the time t1 is calculated (step 203), and then the change of the current value at the time t1 in the predetermined time ΔT. Amount (ΔA)
Is calculated (step 204), and the time differential value (dV / dt = e) of the voltage for detecting the low battery is set according to ΔA (step 205).

It is erroneous to set the reference value e according to ΔA by increasing the reference value e in an extremely abrupt portion of the current change, as shown in (d) of FIG. 3 (e). This is to avoid detection.

Next, it is determined whether or not “ΔA ≧ N0 (predetermined current change amount)” (step 206).

If “ΔA ≧ N0” is not satisfied, it is determined whether or not “| M1 | ≧ e” is satisfied (step 207). If “| M1 | ≧ e” is satisfied, the battery voltage time is set to the value of the reference value e. The low battery is detected assuming that the absolute value of the differential value has reached (portions (b) and (c) of FIG. 3 (b)). Therefore, the difference in the remaining amount of the battery at the time when the low battery is detected between the fully charged battery and the short-time charged battery (corresponding to the difference between the times c and d in FIG.
Are almost equal. In this case, the display 5 displays a low battery (step 208). If “| M1 | ≧ e” is not satisfied, the process returns to step 201.

If “ΔA ≧ N0” in step 206, a predetermined time (Δ
t) Stand by (step 209). This is to prevent the low battery from being detected when the current changes abruptly (for example, part (e) of FIG. 2 (e)). That is, when the current change is rapid like this, the voltage differential value
M1 may suddenly decrease (Fig. 3 (e)) and exceed the reference value e, but in order to prevent the low battery from being detected at such a time, a certain time has passed since the time when the current change occurred. Erroneous detection is prevented by comparing the voltage differential value M2 after Δt with the reference value e.

That is, when the current change ΔA is larger than N0 in step 206, a certain time Δt is waited from that time (step 20
9), NiCd battery 1 at that time t2 (t2 = t1 + Δt)
Measure the voltage value (V2) and current value (A2) of the
0), and the time differential value (dV / dt = M2) of the voltage value at time t2 is calculated (step 211).

Next, it is determined whether or not “| M2 | ≧ e” (step 21
2) If “| M2 | ≧ e”, the low battery is displayed on the display unit 5 (step 208), and if not “| M2 | ≧ e”, the process returns to step 201.

Thus, in the present embodiment, even when a low battery is detected for batteries having different charge capacities, there is no significant difference in the remaining capacity at the time of detection.

In the present embodiment, the power supply for detection is a nicad battery, but needless to say, another power supply may be used.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a low battery detection device in which the remaining amount of the battery at the time of detecting the low battery is substantially constant even when the charging state of the battery is different. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a low battery detection device according to an embodiment of the present invention, FIG. 2 is a flow chart showing the operation of the low battery detection device of this embodiment, and FIG. 3 is a discharge characteristic of a battery. It is a graph which shows. 1 ... Battery, 2 ... Resistance, 3 ... A / D converter, 4 ...
… Microcomputer, 5 …… Display

Claims (2)

[Scope of utility model registration request] 1. A voltage value detecting means for detecting a voltage value of a battery, a judging means for judging whether the voltage value is a first predetermined value or less, and an absolute value of a time differential value of the voltage value. A voltage differential value calculating means, a change amount calculating means for calculating a current value change amount of the battery at a predetermined time ΔT, the voltage value being equal to or less than a first predetermined value, and an absolute value of the voltage differential value. Is a second predetermined value or more set according to the amount of change in the current value, and a detection means for detecting the low battery state of the battery. 2. A voltage value detecting means for detecting a voltage value of a battery, a judging means for judging whether the voltage value is a first predetermined value or less, and an absolute value of a time differential value of the voltage value. A voltage differential value calculation means, a change amount calculation means for calculating a current value change amount of the battery at a predetermined time ΔT, the voltage value being equal to or less than a first predetermined value, and the current change amount being a second value. A detection means for detecting the low battery state of the battery when the absolute value of the voltage differential value is equal to or lower than a predetermined value and is equal to or higher than a third predetermined value which is set according to the current value change amount. Low battery detection device.