JP2747601B2 - Battery charger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a battery charger for charging a nickel cadmium battery and a lead storage battery, and more specifically, by detecting the internal resistance of a battery, The present invention relates to a battery charger for controlling charging.

<Prior Art> When charging a nickel-cadmium battery, a −ΔV detection method that focuses on the property that the terminal voltage of the battery decreases upon completion of charging is generally used. It is common to employ a detection method that utilizes the fact that the terminal voltage rises sharply as completion approaches.

However, in the case of a charging device that requires charging of both the nickel cadmium battery and the lead storage battery, as a method for simplifying the device, the internal resistance during charging of both the nickel cadmium battery and the lead storage battery is reduced. There is proposed a charging control method that focuses on the similarity of the changes.

As a method of realizing this method, intermittent constant current charging is performed at intervals of several seconds, and the difference between the terminal voltages of the battery at the time of charging and at the time of non-charging is taken out. Therefore, the voltage of this difference is compared with the reference voltage, and when the difference voltage becomes higher than the reference voltage, the internal resistance is high and the charging is sufficiently performed, and the charging is stopped. Have been.

<Problem to be Solved by the Invention> The above-described method of controlling charging by detecting the internal resistance enables charging control of both a nickel cadmium battery and a lead storage battery by a set of control circuits. However, since the internal resistance varies greatly depending on the temperature around the battery, even if the same internal resistance is indicated, it cannot be said that the battery is in an optimal state of charge. There has been a problem that the charge amount is insufficient or the battery is deteriorated due to overcharging.

The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a battery charger capable of always performing optimal charging regardless of an ambient temperature.

<Means for Solving the Problems> The battery charger of the present invention for solving the above problems intermittently supplies a constant current charging current to charge a nickel cadmium battery and a lead storage battery. When a nickel cadmium battery and a lead storage battery are used as a battery to be charged, a voltage dividing circuit that divides a terminal voltage of the battery to be charged, and a voltage dividing circuit when a charging current is supplied. A voltage storage circuit for storing an output voltage of the circuit, a diode having an output connected to the anode of the voltage storage circuit, and a comparator for comparing a voltage output from a cathode of the diode with an output voltage of the voltage dividing circuit. And a configuration for controlling charging according to the output of the comparator is adopted.

<Operation> The terminal voltage of the battery to be charged in the intermittent non-charging state is V1, the terminal voltage of the battery to be charged in the immediately preceding charging state is V2, the voltage dividing ratio of the voltage dividing circuit is N, and Assuming that the output voltage of the voltage divider circuit in the non-charged state is V1a and the voltage output from the voltage storage circuit is V2a, the voltage storage circuit stores the output voltage of the voltage divider circuit immediately before the non-charged state. Therefore, the voltages V1a and V2a are expressed as V1a = V1 / N V2a = V2 / N, and the difference between these two voltages V1a and V2a is a voltage proportional to the internal resistance of the battery to be charged.

The voltage V1a is led to one input of the comparator, and the output of the voltage storage circuit is passed to the other input through the diode in the forward direction. Then, the comparator compares the voltage V1a with the voltage V4 (where V4 = V2a−V3).

On the other hand, even when the batteries to be charged are in the same state of charge, the internal resistance tends to decrease as the temperature rises. , The voltage difference (denoted as V2a-V1a) becomes smaller. However, since the forward voltage V3 of the diode decreases as the temperature rises, the difference between the voltage V1a and the voltage V4 increases. That is, the voltage difference (V2a−V1a) caused by the change in the internal resistance of the rechargeable battery caused by the temperature.
JSD) is canceled out by the voltage change caused by the temperature change of the forward voltage of the diode.

<Embodiment> FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

In the figure, a positive output of a power supply circuit 19 that generates power for charging is a constant current circuit that makes the charging current constant, a switch that opens and closes the charging circuit, a start timer that controls the operation at the beginning of charging, and a supplementary circuit. It is connected to the anode of a diode D2 for preventing backflow through a current control circuit constituted by a sub timer for controlling charging.

The cathode of the diode D2 is connected to one terminal of the resistor R1 and the positive terminal of the battery 11 to be charged. The negative output from the power supply circuit 19 is formed by a resistor, and is connected to the negative terminal of the battery 11 to be charged via a current detection circuit 18 that converts a current value to a voltage value.

The other terminal of the resistor R1 is a resistor with one terminal grounded.
Connected to the other terminal of R2,
The amplifier 15 is led to each plus input. The output of the OP amplifier 15 is connected to its own negative input and the negative input of the comparator 16, and the OP amplifier 13
The output of 1 is led to the anode of diode D3.
The cathode of the diode D3 is connected to the other terminal of the capacitor C1 whose one terminal is grounded and the gate of the FET Q1.

The drain of the FET Q1 is connected to the positive power supply P, and the source is guided to the negative input of the OP amplifier 131 and the anode of the diode D1. The cathode of the diode D1 is connected to the other terminal of the resistor R3 whose one terminal is grounded, and to the plus input of the comparator 16. The output of the current detection circuit 18 and the output of the comparator are led to the current control circuit 17.

In the above configuration, the voltage dividing circuit 12 has two resistors R1 and R2.
The voltage storage circuit 13 includes an OP amplifier 131,
It is composed of a diode D3, a capacitor C1, and an FET Q1.

The operation of the embodiment of the present invention will be described below. First, the operation of the voltage storage circuit 13 will be described, and then the entire operation will be described.

The OP amplifier 131 in the voltage storage circuit 13 operates so that the output voltage of the voltage dividing circuit 12 and the source voltage of the FET Q1 become equal, but the output of the OP amplifier 131 is connected via a diode D3 to a holding capacitor. Since the capacitor C1 is connected, the capacitor C1 is charged so that the source voltage and the output of the voltage dividing circuit 12 become equal when the voltage of the plus input increases. However, when the output voltage of the voltage divider 12 drops, the source voltage does not drop because the capacitor C1 is not discharged. That is, the voltage storage circuit 13 stores the maximum voltage of the voltage output from the voltage dividing circuit 12, and outputs the stored voltage.

FIG. 2 is an explanatory diagram showing a change in terminal voltage during charging of a nickel cadmium battery. With reference to the figure, the whole operation of the embodiment of the present invention will be described below.

The current control circuit 17 outputs a pulsed charging current to the battery to be charged.
11 (nickel cadmium battery), the terminal voltage also becomes a voltage P21 that changes in a pulsed manner, and the voltage difference V11 of the pulsed voltage at this time is the charging current flowing through the internal resistance of the battery 11 to be charged. The voltage indicates a voltage drop.

FIG. 3 is an explanatory diagram showing a change in a voltage waveform of a main part.

The terminal voltage of the charged battery 11 in the intermittent non-charged state is V1, the terminal voltage of the charged battery in the immediately preceding charged state is V2, and the voltage dividing ratio of the voltage dividing circuit 12 is N.
The output voltage of the voltage divider circuit in the non-charged state is (V1a−
1) The voltage output from the voltage storage circuit 13 is (V2a−
1), the voltage storage circuit 13 stores the output voltage of the voltage dividing circuit 12 immediately before the non-charged state, so that the voltage (V1
a-1) and (V2a-1) are expressed as (V1a-1) = V1 / N (V2a-1) = V2 / N, and the voltage (V1a-1) changes as indicated by a solid line 52, and the voltage (V2a -1) is a change indicated by the solid line 55 and the dashed line 56.

On the other hand, since the output of the voltage storage circuit 13 is guided to the plus input of the comparator 16 via the diode D1,
Assuming that the forward voltage drop of the diode D1 is (V3-1), the voltage (V3-1) that has dropped from the output of the voltage storage circuit 13 (indicated by the solid lines 52 and 55 and the dashed line 56) is (Indicated by broken line 57).

When the temperature is lower than the above state, the battery 11 to be charged
, The output voltage of the voltage dividing circuit 12 changes as indicated by broken lines 51 and 54, and the width of the voltage change increases as compared with the change width when the temperature is high.

Therefore, assuming that the output voltage of the voltage dividing circuit when the temperature is low and in the non-charging state is (V1a-2) and the voltage output from the voltage storage circuit 13 is (V2a-2), (V1a-1) = (V1a-2) (V2a-1) <(V2a-2).

In addition, the voltage drop due to the diode D1 at this time is (V3−
If (2), then (V3-1) <(V3-2).

Therefore, immediately after the time T11, the voltage guided to the plus input of the comparator 16 is equal to that when the temperature is high (V4−
1) When it is taken as (V4-2) when it is low, (V4-1) = (V2a-1)-(V3-1) (V4-2) = (V2a-2)-(V3-2) Becomes

On the other hand, since the terminal voltage of the battery 11 to be charged is divided by the voltage dividing circuit 12, (V2a-2)-(V2a-1) ≒ (V3-2)-(V3-1).

Therefore, the voltage change of the positive input of the comparator 16 when the temperature is low is a change similar to the voltage change when the temperature is high (indicated by a broken line 57), and the time when the charged battery 11 is sufficiently charged is At T11, the levels of the plus input signal and the minus input signal are inverted, and the output is inverted.

As a result, the current control circuit 17 changes the charging current to half the current value, activates the operation of the sub-timer 13, and performs auxiliary charging for complete charging (indicated by the solid line 58 or the broken line 59). Thereafter, charging is ended at time T12.

The change in the internal resistance of the lead storage battery also shows the same change (the internal resistance decreases as the temperature rises, and the internal resistance increases as the temperature decreases), so that the operation at the time of charging is the same as that described above. Therefore, a detailed description of the operation is omitted (however, in the case of a lead-acid battery, a change in the terminal voltage indicates a change that rapidly increases as the charging approaches completion).

Note that the present invention is not limited to the above-described embodiment. When the input resistance of the comparator 16 is large, it is possible to adopt a configuration in which the OP amplifier 15 is omitted.

Further, the voltage at the time of the initial t1 of the charging stored by the voltage storage circuit 13 is configured to be reduced by spontaneous discharge due to leak.However, in order to further ensure the discharge, at time T13 at which the initial charging is completed, It is possible to adopt a configuration in which a circuit for discharging the capacitor C1 is added.

<Effect of the Invention> The battery charging device according to the present invention stores the terminal voltage of the battery to be charged divided by the voltage dividing circuit by the voltage storage circuit, and outputs the output to the diode connected in the forward direction. Through the comparator through which
Since the output of the voltage divider circuit and the output of the voltage storage circuit are compared, the change in the terminal voltage of the battery to be charged due to the temperature change is offset by the change in the forward voltage drop of the diode. Therefore, it is possible to always perform optimal charging regardless of the ambient temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a change in terminal voltage during charging of a nickel cadmium battery, and FIG. 3 is a voltage waveform of a main part. FIG. 9 is an explanatory diagram showing a change in the state of the first embodiment. 11 Battery to be charged 12 Voltage divider circuit 13 Voltage storage circuit 16 Comparator D1 Diode.

Claims (1)

(57) [Claims] 1. A battery charger for charging a nickel cadmium battery and a lead storage battery by intermittently supplying a constant current charging current, wherein the nickel cadmium battery and the lead storage battery are to be charged. A voltage dividing circuit that divides a terminal voltage of the battery to be charged; a voltage storing circuit that stores an output voltage of the voltage dividing circuit when a charging current is supplied; and an output of the voltage storing circuit to an anode. A connected diode, and a comparator for comparing a voltage output from a cathode of the diode with an output voltage of the voltage dividing circuit, wherein charging is controlled in accordance with an output of the comparator. Battery charger.