JPH0548056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for detecting full charge of a nickel-cadmium battery.

(b) Prior Art In general, the charging voltage characteristics of a nickel-cadmium battery are as shown in FIG. 1, with a peak voltage occurring near full charge. It is thought that this is because when the battery is fully charged, oxygen is generated at the anode of the nickel-cadmium battery, and the oxygen undergoes a recombination reaction on the cathode, resulting in a decrease in the charging voltage.

Conventionally, when charging a nickel-cadmium battery, a method has been adopted in which charging is stopped by detecting that the terminal voltage of the battery, that is, the charging voltage has reached a predetermined value. In this case, the closer the detection voltage is to the peak voltage shown in Figure 1, the more the amount of charge will increase. However, due to variations in nickel-cadmium batteries, the peak value of the charging voltage is not necessarily constant, and the detection voltage may be increased. If the setting is too high, it will become impossible to detect batteries in which the peak voltage is less than the detection voltage. Therefore, the detection voltage must be set to a certain level lower than the peak voltage to ensure reliable detection. However, in this case, there is a drawback that charging is stopped before the battery is fully charged.

(c) Purpose of the Invention The present invention has been made in view of the above-mentioned points, and an object of the present invention is to reliably detect full charge even in the case of variations in nickel-cadmium batteries.

(D) Structure of the Invention The present invention provides an A-D conversion means for converting the output of a temperature detector that detects the terminal voltage of a nickel-cadmium battery and the surface temperature of the nickel-cadmium battery into digital values; and a control means for detecting full charge based on data from the D conversion means,
After a predetermined period of time has elapsed from the start of charging, the terminal voltage and surface temperature of the nickel-cadmium are detected at a predetermined cycle, and the terminal voltage is reduced by a predetermined value from the maximum value, and the surface temperature is a predetermined value from the initial temperature. By having a configuration that detects that the battery has risen, full charge is detected and charging is stopped.

(E) Example Charging of a nickel-cadmium battery has the characteristics shown in Figure 1. However, in a battery that has been left in an over-discharged state for a long period of time, the electrodes have become inactive, and when this battery is charged, As shown by the broken line in FIG. 2, one peak occurs immediately after the start of charging. Furthermore, as described above, when the battery is nearly fully charged, oxygen generated at the anode undergoes a recombination reaction on the cathode, which generates reaction heat. Furthermore, due to heat generation due to the specific resistance inside the battery, the surface temperature of the battery increases as shown in FIG. On the other hand, a battery immediately after use has a high surface temperature due to its discharge current, and the temperature characteristics when charging with this current decrease immediately after charging starts, as shown by the broken line in FIG. Therefore, in the present invention, in order to prevent erroneous detection, the detection operation is not performed for a predetermined time _t1 from the start of charging, and after the elapse of the predetermined time _t1 , the detection operation is performed periodically.
Detection operation is performed at t ₂ .

FIG. 3 is a circuit diagram showing an embodiment of the present invention. The cathode of the nickel-cadmium battery 1 is grounded, and the anode is connected to a charging power source via a current control device 2.
Connected to V _C. The current control device 2 is controlled by the control output B of the control means 3, becomes conductive at the start of charging, supplies a constant charging current to the battery 1, and cuts off the charging current when charging is stopped. A temperature detector 4, such as a thermistor, is provided near the nickel-cadmium battery 1, and a voltage is supplied to the temperature detector 4 from a power source _VDD via a resistor _R1 . The A-D converting means 5 consists of two comparators 6 and 7 and resistors R ₂ , R ₃ , R ₄ , R ₅ and R ₆ , and one input of each comparator 6 and 7 has a resistor R _{2 .} The power supply voltage V _DD is supplied through the connection point between one input of each comparator 6, 7 and the resistor R ₂ and the four output terminals A ₁ , A ₂ , A ₃ , A ₄ of the control means 3. Resistors R ₃ , R ₄ , R ₅ , and R ₆ are connected between them. The resistors R ₃ , R ₄ , R ₅ , and R ₆ are weighted as is well known, and by outputting binary codes to the output terminals A ₁ , A ₂ , A ₃ , and A ₄ , the comparators 6 and 7 One of the input voltages changes in a stepwise manner. Further, the terminal voltage of the nickel-cadmium battery 1, that is, the charging voltage, is applied to the other input of the comparator 6, while the terminal voltage of the temperature detector 4 is applied to the other input of the comparator 7, Output COM-V and COM-T of each comparator 6, 7
is applied to the control means 3. That is, in the A-D conversion, every time "1" is added to the 4-bit counting means, the counted contents are outputted to the output terminals _A1 to _A4 , and
This is done by determining the outputs of the comparators 6 and 7 at that time, and the charging voltage and temperature can be converted into digital values.

When the charge start signal C _ST is applied, the control means 3 makes the current control device 2 conductive and starts charging by the control output B, but does not perform the detection operation for a predetermined time period t ₁ thereafter and performs the predetermined detection operation. The detection operation is performed every predetermined period t ₂ after the elapse of time t ₁ , and the control means 3 is constituted by, for example, a microcomputer.

The operation of the control means 3 described above will be explained using the flow diagram shown in FIG. When the charge start signal _CST is applied, the control means 3 outputs the signal B to turn on the current control device 2 and start charging. Next, a 10-minute timer is set inside the control means 3, and no detection operation is performed until the 10-minute timer counts up. In other words, the time set in this timer is
The time t ₁ shown in the figure. When the timer count-up is detected, the temperature is converted from analog to digital. The A-D conversion is performed using, for example, 4
A bit counter is set, and each time "1" is added to or subtracted from this counter, the contents of the counter are output to the output terminals _A1 to _A4 , and the output COM-T of the comparator 7 at that time is determined. The counter data when they match is set as the converted value. The temperature data T1 obtained by this first A-D conversion is the temperature data _T1 of the nickel-cadmium battery 1.
This is the initial temperature, and is thereafter stored in the internal memory of the control means 3 as a reference temperature for comparison.

Then, the following detection operation is repeated every predetermined period _t2 . First, the charging voltage is A-D converted by the same operation as described above, and the converted voltage data is
It is determined whether Vn is larger than a predetermined value. this is,
It detects that the charging voltage Vn has increased abnormally, and the predetermined value is set to, for example, 2.0V.
When charging voltage Vn exceeds 2.0V, signal B is turned OFF.
As well as stopping charging, a warning signal ALM
output, emit a warning, for example by sound, and stop the operation. Charging voltage Vn is smaller than the set value,
If no abnormality is detected, determine whether the charging voltage Vn at that time is larger than the highest value Vα of the charging voltage detected in the detection operation up to that point,
If it is larger, the highest value Vα up to that point is rewritten to the charging voltage Vn at that time. If it is smaller than the maximum value Vα, it is determined that the maximum value Vα is a peak value that occurs near full charge, and it is determined whether Vα−Vn is a predetermined voltage difference ΔV. As shown in FIG. 2, the voltage difference ΔV is a voltage difference that decreases from the peak value, and is set to, for example, 0.02V. Therefore, Vα
-Vn is equal to or greater than the voltage difference △V, the full charge flag (FLG) is set in the memory in the control means 3.
is set, and if the voltage difference is smaller than ΔV, the full charge flag (FLG) is not set. The detection of the charging voltage is completed by the above operation, and then the surface temperature detection operation is performed.

In the surface temperature detection operation, first, analog-to-digital conversion of the temperature is performed in the same manner as described above, and it is determined whether the converted temperature Tn at that time is larger than a predetermined value. This is to detect that the surface temperature Tn has increased abnormally, and the predetermined value is, for example, 50℃.
When the surface temperature Tn is set to 50℃ or higher,
At the same time as turning off signal B and stopping charging,
It outputs a warning signal ALM, issues an acoustic warning, for example, and stops the operation. If the surface temperature Tn is smaller than the set value and no abnormality is detected, the previously detected initial temperature _T1 and the temperature at that time
It is determined whether the difference from Tn, that is, Tn - T ₁ is greater than or equal to the temperature difference ΔT. From the characteristic diagram shown in FIG. 2, the temperature difference ΔT is the temperature rise at the point where full charge is to be detected, and is set to, for example, 6°C. Here, if Tn-T ₁ is greater than or equal to △T, it is a condition for full charging. At this time, it is determined whether the fully charged FLG is set, and if the FLG is set, the temperature and Since both voltage conditions indicate full charge, signal B is turned OFF to stop charging and complete the operation. On the other hand, if Tn-T ₁ is smaller than △T, or if the fully charged FLG is not set, a 1-minute timer is set, the operation is stopped until the timer counts 1 minute, and after 1 minute the battery is turned off. The voltage detection and temperature detection described above are performed again. That is, the period t ₂ is formed by a one-minute timer.

By operating the control means 3 in this manner, the peak of the charging voltage and the surface temperature are detected, and charging is stopped when the respective conditions for full charging are satisfied.

In the explanation of this embodiment, normal charging (charging for about 1.5 hours until full charge) was explained as an example.
Even in the case of rapid charging (about 30 minutes until full charge), the present invention can be implemented by appropriately changing the set values.

(F) Effects of the Invention As described above, according to the present invention, even if there are variations in the remaining capacity and characteristics of nickel-cadmium batteries, it is possible to reliably detect the full charge of each battery, and also to detect the full charge during charging. Since abnormalities can also be detected, this has the advantage of improving charging efficiency.In particular, when adding a charging function to electronic equipment using a CPU or the like, it has the advantage of requiring fewer external components.

[Brief explanation of the drawing]

1 and 2 are charging characteristic diagrams of a nickel-cadmium battery, FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is a flowchart showing the operation of the embodiment shown in FIG. 3. It is a diagram. 1... Nickel-cadmium battery, 2... Current control device, 3... Control means, 4... Temperature detector,
5... A-D conversion means, 6, 7... Comparator.

Claims (1)

[Claims] 1. A current control device that controls the supply of charging current to the nickel-cadmium battery, a temperature detector that is placed near the surface of the nickel-cadmium battery and detects its surface temperature, and a temperature detector that controls the terminal voltage and temperature of the nickel-cadmium battery. comprising an A-D conversion means for inputting the terminal voltage of the temperature detector and converting each value into a digital value, and a control means for detecting full charge based on data from the A-D conversion means, The control means operates after a predetermined time has elapsed from the start of charging, detects the terminal voltage and surface temperature of the nickel-cadmium battery at a predetermined period, and causes the terminal voltage of the nickel-cadmium battery to decrease by a predetermined value from the maximum value. A full charge detection method for a nickel-cadmium battery, further comprising: cutting off the current control device to stop charging when it is detected that the surface temperature has increased by a predetermined value from an initial value.