JPH03245740A - Charger - Google Patents

Abstract

PURPOSE:To suppress generation of gas in a battery and to prevent thermal runaway of an Ni-Cd cell by providing means for rectifying an AC input, means for detecting a battery voltage, control means for limiting a charging current, and means for holding an operation when the control means is operated. CONSTITUTION:When charging is started, a commercial AC is rectified, and an Ni-Cd cell then starts charging. The cell is charged near in a full-charging state soon, and its charging voltage is abruptly raised, but if the environmental temperature is high, charging is continued with substantially the same charging current as that at the initial time, and charged in short time. On the other hand, if the environmental temperature is low, when the cell is charged near to the full-charging state, the fact that the charging voltage reaches a predetermined voltage is detected by voltage detecting resistors R1, R2 to conduct a control transistor Q1. In this case, a voltage holding resistor R3 holds the voltage dividing point of the resistors R1, R2 at a predetermined value or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a charger that suppresses gas generation that occurs when the charging voltage of a battery increases.

(b) Conventional technology Generally speaking, when Ni-Cd batteries are charged at a low ambient temperature, the charging voltage increases due to an increase in internal resistance, etc., and the charging voltage eventually stops.
It is known that when the pressure reaches a predetermined value, gas is generated. Furthermore, it is known that the charging voltage increases even when the charging current is increased regardless of the ambient temperature.

Therefore, when charging at a low ambient temperature, it is necessary to limit the charging current so that the charging voltage does not reach the gas generation voltage, and to prevent the charging voltage from increasing.

On the other hand, as disclosed in Battery Handbook 1st Edition (Denki Shoin) 3157, there is a charging circuit for a rechargeable alkanomanganese battery that has a simple circuit configuration and charges the battery at a constant voltage. That is, a relatively large current flows in the initial stage of charging, and when the charging voltage eventually rises and reaches a predetermined value, the charging current is reduced. in this case,
Since the predetermined value is set much lower than the gas generation voltage, even if the charging voltage has not reached the gas generation voltage, if it reaches the predetermined value, the charging current will decrease and it will take a long time to reach full charge. It takes time.

In addition, when attempting to charge a Ni-Cd battery using such a circuit, there is a drawback that a thermal runaway phenomenon occurs in which when the charging current decreases to below the predetermined value at the end of charging, the charging current increases again. There is.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above points, and is a charger that suppresses gas generation within the battery and prevents the thermal runaway phenomenon of N1-Cd batteries. Our goal is to provide the following.

(d) Means for solving the problem A charger for charging a battery includes a rectifying means for rectifying an AC input, a voltage detecting means for detecting the battery voltage of the battery to be charged, and a voltage detected by the detecting means for detecting the battery voltage of the battery to be charged. The present invention includes a control means that limits the charging current to the battery to be charged when a value close to the gas generation voltage of the battery is reached, and a holding means that maintains the operation when the control means operates.

(E) Operation When a battery to be charged is set in the charger of the present invention and charging is started, the commercial alternating current is rectified by the rectifier and then a charging current is supplied to the battery to be charged, and the -blade pressure detection means detects the battery voltage. Detect. As charging progresses, the battery voltage eventually rises and reaches near the gas generation voltage, and the voltage detection means detects this and operates the control means. As a result, the control means reduces the charging current, thereby suppressing an increase in battery voltage and suppressing gas generation. Also, at this time, the holding means is adapted to hold the operation when the control means operates, so that the charging current is held in a reduced state and when charging the Xl-Cd battery. It is possible to prevent a thermal runaway phenomenon in which the battery voltage drops at the end of charging and is charged again with a relatively large charging current at the beginning of charging.

(f) Example Embodiments of the present invention will be described in detail below with reference to the drawings.

In Figure 1, T is a transformer that transforms commercial AC, and D
and C are a rectifier diode and a smoothing capacitor as rectifier means. Further, R1 and R2 are detection resistors serving as voltage detection means, and are connected to both ends of the Ni--Cd battery B to detect the battery voltage. DZ and Ql are a constant voltage diode and a control transistor as control means, and the constant voltage diode DZ is inserted between the voltage dividing point of the detection resistors R1 and R2 and the base of the control transistor Q1. At the same time, the main current path of the control transistor Q1 is connected to the charging current supply line. Then, when the detection resistor detects a predetermined voltage, the control transistor Q is connected via the constant voltage diode DZ.
1, the main current path is made conductive, and the charging current is limited. R3 is a voltage holding resistor as a holding means, and is inserted between an example of the charging current supply line and the voltage dividing point of the detecting resistors R1 and R2. This voltage holding resistor R3 maintains the voltage at the voltage dividing point of the detecting resistors R1 and R2 at a predetermined value or higher when the detecting resistor detects a predetermined voltage and makes the control transistor Ql conductive. It maintains conduction of the transistor. Further, S is a button switch for starting, which is manually closed instantaneously to start.

In the above configuration, the operation of the charger of the present invention is controlled by the second
This will be explained with figures. In Figure 2, the ambient temperature is 0.1
It shows the change in charging voltage and charging current over time at a temperature of 0.20.40°C. Further, a in the figure indicates the above-mentioned predetermined voltage, which is a value slightly lower than the gas generation voltage of the Ni-Cd battery (1, 56~'/Ce1l).

Now, when a Ni-Cd battery is set in the charger of the present invention and charging is started, the commercial alternating current is rectified by the rectifier and then N
1 = Supply charging current to Cd battery. At this time, the charging current is approximately constant, and the lower the ambient temperature, the higher the charging voltage, and increases as charging progresses. Eventually, the charge tJE becomes close to full charge and the charging tJE rises rapidly, but when the ambient temperature is high at 20°C to 40°C, the charging current does not reach the predetermined voltage (a in the figure), which is almost the same as in the initial stage of charging. Charging continues, and charging is performed in a short time without reducing the charging current. On the other hand, in the case of a low ambient temperature of 0.10° C., the voltage detection resistors R1 and R2 detect that the charging pressure has reached a predetermined voltage as the charge approaches full charge, and the control transistor Q1
By making it conductive, the charging current is rapidly reduced, suppressing the increase in the charging voltage and suppressing gas generation.

At this time, the voltage holding resistor R3 maintains the voltage at the voltage dividing point of the detecting resistors R1 and R2 at a predetermined value or higher when the detecting resistor detects a predetermined voltage and makes the control transistor conductive. , maintains conduction of the control transistor.

Therefore, even if the charging voltage rapidly increases and then decreases near full charge, which is characteristic of Ni-Cd batteries, the holding means maintains the state in which the charging current is decreased, so that the charging voltage remains below the predetermined voltage. Thermal runaway reduction does not occur when the temperature drops below.

FIG. 3 is an electric circuit diagram showing another embodiment, in which a switching transistor Q2 is inserted into the + side line of the charging current supply line, and the base of the switching transistor Q2 is connected to the main current path of the control transistor Q. It is connected to. Therefore, when the control transistor Q1 becomes conductive, the switching transistor Q2 is made non-conductive to limit the charging current.

(1) Effect of the Invention As described above, according to the present invention, when the voltage detection means detects a voltage slightly lower than the gas generation voltage, the charging current is limited by the operation of the control means, so gas generation can be suppressed. Since a holding means is provided for holding the operation of the control means when it operates, the thermal runaway phenomenon seen in N-nee Cd batteries does not occur.

[Brief explanation of drawings]

The drawings show the charger of the present invention, FIG. 1 is an electric circuit diagram showing one embodiment, and FIG. 2 is an electric circuit diagram showing an embodiment of the charger, and FIG.
Time change diagram of charging voltage and charging current at 0.40°C,
FIG. 3 is an electrical circuit diagram showing another embodiment. B ・N1-Ccl battery, R1, R2 detection resistor, R3
・Voltage holding resistor, DZ... Constant voltage diode, Ql...
・Control transistor, Q2・ Switching transistor.

Claims (1)

[Claims] (1) A charger for charging a battery includes a rectifying means for rectifying AC input, a voltage detecting means for detecting the battery voltage of the battery to be charged, and a detection voltage of the detecting means is close to the gas generation voltage of the battery to be charged. 1. A charger comprising: a control means that limits the charging current to a battery to be charged when a charging current reaches a certain value, and a holding means that maintains the operation when the control means operates.