Design of intelligent management system for nickel-cadmium rechargeable batteries based on single chip microcomputer

As an alkaline battery, nickel-cadmium rechargeable batteries have special requirements for use, management and maintenance. If they are not managed well, used improperly, or maintained in time, they can easily lead to battery aging, failure, or even scrapping. Aiming at the different types of nickel-cadmium rechargeable batteries that are used in large quantities and stored in centralized locations in the military, factories, and mines, a battery intelligent management system has been designed using single-chip microcomputer control technology to perform intelligent management of nickel-cadmium rechargeable batteries, such as automatic status detection, charge and discharge management, and performance maintenance.

Through the automatic management of nickel-cadmium rechargeable batteries, the blindness and arbitrariness in the use and management of nickel-cadmium rechargeable batteries can be effectively eliminated, the use efficiency of nickel-cadmium rechargeable batteries can be improved, and the service life of nickel-cadmium rechargeable batteries can be extended.

The special requirements for the use, management and maintenance of nickel-cadmium rechargeable batteries are mainly reflected in the following: 1) They must be stored in suitable temperature conditions and non-acidic environment; 2) Batteries should be maintained regularly when stored for a long time, and the initial capacity of new batteries must be restored before they are used; 3) Single cells with large performance differences cannot be used or charged in the same group, and scrapped batteries (or faulty batteries) cannot be mixed with usable batteries; 4) Batteries should be discharged to the termination voltage before charging to eliminate the "memory effect" that may be produced by nickel-cadmium rechargeable batteries, and overcharging and over-discharging of the batteries should be avoided; 5) Pulse charging should be used as much as possible to improve the charging efficiency of the battery and extend the battery life.

The intelligent management system for nickel-cadmium rechargeable batteries designed and manufactured can meet the special requirements of nickel-cadmium rechargeable batteries for use, management and maintenance through centralized storage of batteries and automatic charge and discharge management.

1 System role and function

The intelligent management system for nickel-cadmium rechargeable batteries is used to intelligently manage nickel-cadmium rechargeable batteries that are used in large quantities and stored centrally. It mainly completes functions such as battery storage, automatic battery detection and automatic charge and discharge management, battery maintenance and initial capacity recovery, battery fault detection and indication alarm, battery reverse polarity indication alarm, battery no-load indication and temperature control. The system functional block diagram is shown in Figure 1.

Figure 1 System functional block diagram

2 System composition and principle

The system consists of a control module, a battery detection module, a charge and discharge module, a battery switching module, a temperature control module, a battery storage module and a power module. Among them, the control module consists of a single-chip microcomputer and peripheral circuits, which are used to realize charge and discharge control, battery switching control, temperature control, battery detection and indication control; the charge and discharge module consists of a charge and discharge circuit, which is used to realize the charging and discharging of rechargeable batteries; the switching module consists of a relay and its control drive circuit, which is used to realize automatic or manual switching between battery cells. The temperature control module consists of a temperature sensor, an axial fan and a control circuit, which is used to monitor and control the temperature of the battery storage environment. After the system starts working and passes the self-test, it first detects the battery status, removes the faulty battery and corrects the reverse battery, and then enters the battery management stage to charge and discharge the battery cells in sequence. After a management cycle ends, the system starts the next management cycle after a certain delay. The system principle block diagram is shown in Figure 2.

Figure 2 System principle block diagram

3 Hardware Design

3.1 Control module design

The AT89S52 microcontroller is selected as the control unit. The P0 port of the microcontroller is used for digital display and keyboard scanning. Among them, P0.0~P0.3 are used to output the 4-bit binary number corresponding to the battery code, and after being converted by 74LS248 to form a 7-segment code, it is sent to the digital tube display. P0.3 and P0.4 are controlled by timer T0, and cyclically output 4 2-bit binary numbers 00, 01, 10, and 11. After being decoded by decoder 74LS139, they are used as scanning signals to scan the digital tube and matrix keyboard at the same time. P0.5 and P0.6 are used to monitor the status of each key of the 2×4 matrix keyboard. P1 port is used to continuously output 8-bit binary numbers, and after cascade decoding by the two-stage decoder 74LS154, it can output up to 256 control signals to realize automatic switching control of 256 battery cells in sequence. Port P2 is used to detect the status of the rechargeable battery (no load, fault, fully charged, fully discharged) and control the battery charging and discharging. Port P3 is mainly used for battery status (no load, fully charged, fault, reverse connection) monitoring, indication and alarm.

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3.2 Battery switching module design

The battery switching module is composed of a switching circuit array consisting of a drive circuit and a relay. Each switching circuit unit corresponds to a battery cell. The drive circuit is mainly composed of an inverter 74LS04 and a transistor S9013, which is controlled by the control signal output by the P1 port to control the open and closed states of the relay. The double-contact electric relay 4137, which can convert two signals at the same time, is used to achieve simultaneous switching of the charging and discharging circuit and the battery status detection circuit. The interrupt control function of the external interrupt INT1 is used, and the status of the two switching buttons is detected and judged through the P3.6 of the microcontroller. At the same time, the "up" and "down" buttons are used to realize manual switching between battery cells. The switching unit circuit between battery cells is shown in Figure 3.

Figure 3 Battery switching unit circuit

3.3 Charging and discharging module design

The charge and discharge module consists of a charging circuit, a discharging circuit and a charge and discharge control circuit. The charge or discharge control signal output by the microcontroller controls the charge or discharge circuit to charge or discharge the battery. The battery charge and discharge circuit is shown in Figure 4.

Figure 4 Battery charging and discharging circuit

3.4 Voltage detection module design

The voltage detection module consists of a three-terminal voltage regulator circuit, a voltage divider circuit and a comparison circuit. The three-terminal voltage regulator circuit consists of LM317 and its peripheral circuits. The output voltage is divided by the voltage divider circuit and sent to one end of the comparator composed of LM339 as the reference voltage. The voltage collected from the positive electrode of the battery is sent to the other end of the comparator circuit. The current battery power and placement status can be judged from the output level of each comparator. These status signals are sent back to the microcontroller as detection signals, and the microcontroller controls the operation of the charge and discharge circuit and indicates the battery status. The battery voltage detection circuit is shown in Figure 5.

Figure 5 Battery voltage detection circuit

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4 Software Design

The system software consists of monitoring program, automatic management program, system self-check subroutine, battery detection subroutine, manual switching interrupt subroutine, key and digital tube scanning subroutine, etc. After the system starts working, the system self-check subroutine is called first. If the system or a module is not working properly, the system will issue an alarm and the digital tube will flash to display the fault module code. If the system and each module are working properly, the system will call the battery detection subroutine to check and judge the fault, reverse connection and no-load conditions of each battery cell in the system, and synchronously display the location code of the detected battery cell, and indicate the alarm for the detected faulty battery and reverse connection battery. After all batteries are detected, the system automatically enters the battery automatic management program to automatically cycle the battery for charge and discharge management. In the automatic management program, the system first discharges the battery, and then charges it after discharging to the termination voltage. At the same time, during the charging process, the software delay is used to make the nickel-cadmium rechargeable battery discharge briefly during the charging gap, so as to effectively improve the battery charging efficiency in a pulse charging manner and eliminate the polarization phenomenon that may occur in the nickel-cadmium rechargeable battery to the maximum extent. The system workflow diagram is shown in Figure 6.

Figure 6 System workflow diagram

5 Other features

5.1 Temperature Control

Nickel-cadmium rechargeable batteries have certain requirements for the storage environment temperature, so a temperature control module is designed in the system to monitor and control the temperature of the battery environment. The temperature control module consists of a temperature sensor [7], a signal processing circuit, an A/D conversion circuit, a relay and control circuit, and an axial flow fan. When the ambient temperature reaches the set upper limit temperature, the single-chip microcomputer controls the relay to close, thereby controlling the axial flow fan to rotate, thereby ventilating and cooling the battery storage environment. When the ambient temperature reaches the appropriate temperature, the single-chip microcomputer controls the relay to disconnect, and the axial flow fan stops rotating. In this way, the battery storage environment temperature is always kept within the appropriate range.

5.2 Battery Maintenance

For newly activated nickel-cadmium rechargeable batteries or nickel-cadmium rechargeable batteries that have polarized, charge and discharge maintenance is generally required, mainly to restore the initial capacity of the battery and activate its performance. The maintenance method is to perform deep discharge and charge on the battery three times in a row. Once the system is started and the battery is tested, it will always be in the battery automatic management state. If a battery needs to be maintained, the control system can be switched to the battery that needs maintenance by operating the "up" and "down" buttons, and then the "maintenance" button is pressed. The system will interrupt the automatic management and enter the battery maintenance program. After the maintenance is completed, the system continues to perform automatic management.

6 Conclusion

First, the system provides a storage environment with independent space and constant temperature for the nickel-cadmium rechargeable batteries that are centrally placed and uniformly managed, eliminating the adverse effects of acidity, high temperature and other unfavorable factors on nickel-cadmium rechargeable batteries. Secondly, the pulse charging and discharging method is used in the battery charging and discharging management and maintenance process, which not only improves the charging and discharging efficiency of the battery, but also maintains or restores the performance of the nickel-cadmium rechargeable battery. Thirdly, the system adopts the method of discharging first and then charging for charging and discharging management, which can eliminate the "memory effect" that may be produced by nickel-cadmium rechargeable batteries and improve the use efficiency of rechargeable batteries. Fourthly, the battery charging termination and discharge termination voltage are monitored and controlled in real time to avoid overcharging and over-discharging of the battery, which can extend the service life of the nickel-cadmium rechargeable battery. Fifthly, the operation mode of first detection, then management and single-cell charging and discharging is adopted to prevent the occurrence of problems of using or charging single-cell nickel-cadmium rechargeable batteries with large performance differences in the same group.