1. Introduction
As a commonly used device for providing DC power, batteries are becoming increasingly widely used, especially in fields such as power automation equipment, rail transportation, communication, offline solar photovoltaic power generation systems, and military applications that require uninterrupted power supply. The voltage and charging/discharging current of a battery are important indicators reflecting its performance, as well as important judgment parameters for charging and discharging. Therefore, monitoring its voltage and current is a crucial step in the reasonable charging and discharging of the battery. Traditional detection methods rely on tools such as voltmeters to measure the voltage value and then adjust the charging parameters. However, there are problems such as large human errors in recording, poor real-time performance, poor accuracy, unscientific recording, and high detection costs. The introduction of microcomputer technology has promoted the gradual intelligence of battery charging and discharging monitoring systems, achieving real-time monitoring of battery working status. However, the existence of ground potential interference signals, AC interference signals introduced by charging power supply, etc. often causes MCU reset, false acquisition signals, and even direct burning of the main control chip, so it is necessary to choose a awesome signal isolation anti-interference scheme. The following plan will provide a detailed introduction on how to use Guangzhou Jinshengyang ManufacturingIsolation transmitterThe method of using modules to isolate interference signals, transmit signals, and improve the stability and reliability of monitoring systems.
2、 Introduction to Isolation Transmitter
Isolation transmitterA module is a signal processing module that uses an electromagnetic isolation scheme to isolate and convert input non-standard industrial signals into standard industrial signals. The Jinshengyang isolation transmitter module adopts a modular and small volume design, which allows users to use it directly without adding any peripheral circuits. This simplifies the user's circuit design, improves the space utilization of the PCB, and facilitates customer analysis of fault causes and maintenance. Due to the use of electromagnetic isolation technology within the module, it has better temperature drift characteristics, linearity, accuracy, conversion speed, and lifespan compared to optocoupler isolation. The signal input and output, power input, and isolated power output (optional) of the module are isolated from each other, with an isolation withstand voltage value of up to 2500VDC, which can effectively isolate interference signals. Compared to isolators on the market, it has a smaller volume, lower cost, higher integration, and can be directly soldered onto PCB boards, greatly simplifying the design and installation of signal acquisition and control systems, and improving the overall stability and reliability of the system.
Product Features:
No tuning required, can be used directly
Modular&Small Volume
Extremely low temperature float (35PPM/℃)
High precision level&high linearity (0.1% F.S.)
High isolation (2500VDC/60s between input, output, and power supply terminals)
High reliability (MTBF>500000 hours)
Industrial grade (working temperature range: -25 ℃~71 ℃)
3、 Introduction to the principle block diagram of isolation transmitter
Isolation transmitterIt is an electrical device that can convert the measured electrical signal into a linearly proportional output of electrically isolated electrical signals. As shown in Figure 2, the isolated transmission module is divided into four parts: power input part, isolated power output part (optional for customers), signal input part, and signal output part. Its working principle is to first modulate and transform the measured signal through semiconductor devices, then perform electromagnetic isolation conversion through a signal transformer, and then convert it into the required signal at the output end. At the same time, the power supply of the isolated signal is isolated to ensure electrical isolation between the power supply end, isolated power output end, signal input end, and signal output end, effectively isolating signal interference and enabling the main control chip to work stably and reliably.
4、 Application of Isolation Transmitter in Battery Charge and Discharge Monitoring System
When the battery is fully charged, it will directly supply power to the downstream DC load. The supply voltage and current of the battery gradually decrease with the consumption of electricity. If the battery cannot be replenished even after reaching the lowest limit, it is highly likely to be damaged due to overdischarging; On the other hand, when the battery is low and the charger charges the battery, the battery voltage will gradually increase as the battery is replenished. If the battery voltage reaches the limit and still does not stop charging, the battery is highly susceptible to damage due to overcharging. Therefore, real-time and high-precision monitoring of battery voltage and current is necessary, otherwise the battery is prone to damage due to overcharging or overdischarging.
The circuit diagram of our designed battery charging and discharging monitoring system is shown in Figure 3, which mainly consists of a charger, power circuit, battery, DC load, voltage and current sampling circuit, EMC circuit, isolation transmitter, etc MCU、 Composition of display circuit, alarm circuit, etc. Below is a detailed introduction to the functions of each part:
4.1 Control circuit power supply scheme
We have selected the AC-DC module power supply LH05-10B05 manufactured by Jinshengyang Company for the control circuit power supply, which is used to power the isolation transmitter module, AD converter, MCU, and LCD. This module outputs 5V, 1A, which meets the requirements of power supply voltage and power, and has advantages such as input voltage range, AC/DC dual-use, low power consumption, high reliability, and safe isolation. The product is safe and reliable, with good EMC performance. The EMC and safety specifications meet the standards of IEC61000, UL60950, and IEC60950, and have obtained various certifications such as UL and CE.
4.2 Voltage and current sampling circuit scheme
For monitoring battery voltage, we know that common battery voltages include 24V and 12V. In order to facilitate voltage signal acquisition, we use voltage division to reduce the battery voltage to the range of 0-5V for signal processing; For monitoring the charging and discharging current, we connect a shunt in series into the charging and discharging circuit. The shunt converts the discharging current into a millivolt voltage signal for signal processing.
4.3 EMC Circuit Scheme
The design of EMC circuits is often the most easily overlooked but extremely important part of signal isolation processing. We know that the EMC environment in the power grid of industrial sites is extremely harsh, with various interference signals present. Due to the direct connection of the battery pack to the charger and DC load through the same line, the interference signals (such as surge interference) in the power circuit will couple with the signal circuit to the subsequent signal processing circuit, causing signal processing devices to malfunction or be damaged. Therefore, it is necessary to add EMC circuits before signal isolation to absorb interference signals.
4.4 Signal isolation scheme
In practical applications, it has been found that if the signal is not isolated when charging and discharging the battery, the interference signal of the power circuit will be directly transmitted to the MCU in the later stage through the signal path, resulting in frequent signal loss or even system crash of the MCU. There are two conventional signal isolation methods, electromagnetic isolation and optocoupler isolation. Optocoupler isolation, due to its slow response speed and low transmission accuracy, cannot enable the monitoring system to monitor the battery voltage and discharge current in real-time and with high accuracy. Therefore, we need to choose an electromagnetic isolation solution. Here, we have selected the isolation transmitter module manufactured by Jinshengyang Company to isolate interference signals and transmit signals.
In the battery voltage monitoring circuit, we selected the isolation transmitter module T6S6D-3 to isolate and transmit the input 0-5V sampling signal to 0-3V for easy ADC acquisition in the later stage; Because the charging and discharging circuits of the battery use the same line, the voltage signal collected by the shunt in the battery discharge circuit is positive and negative. We have selected the isolation transmitter module TM6S6AP3 from Jinshengyang Company, which can convert the signal line shape that varies from -100mV to+100mV into a voltage signal of 0-3V for direct acquisition by the subsequent ADC.
The advantages of using these two modules are: firstly, they can achieve high electrical isolation between signal input and downstream sampling circuit (isolation voltage of 2500VDC/60S), which can effectively isolate the interference signal of the front-end circuit, so as not to affect the normal operation of the back-end equipment; Secondly, the transmission accuracy of this module is 0.1% F.S, which can meet the high-precision sampling requirements of a 12 bit ADC and accurately monitor the working status of the battery; Again, the isolation transmitter adopts a modular design, which can achieve the isolation and transmission of signals that are not easy to collect by AD (such as 0-5V, -100mV~+100mV) to easily collected signals (0-3V) without any peripheral devices, greatly simplifying the circuit design.
4.5 Data processing, fault alarm and status display
The data processing adopts MCU with integrated high-precision ADC, and the status display adopts 7-segment common cathode circuit digital tube, mainly displaying the current collected voltage value and alarm information. When the voltage is lower than the set value or exceeds the set value, an audible alarm will be issued.
5、 Summary
Due to the significant investment in energy conservation and environmental protection by the government, batteries have experienced rapid development, and new types of batteries have emerged one after another. This has also raised higher requirements for the charging, discharging, and scientific management of batteries, requiring real-time understanding of their working conditions in order to scientifically and reasonably manage and improve their utilization efficiency and service life. This has also promoted the application of battery monitoring systems. However, due to the presence of interference signals in various on-site power circuits, the entire system may not be able to monitor the working condition of the battery in real time, accurately, and reliably, and even damage expensive instrument equipment connected afterwards, causing incalculable losses. The isolation transmitter module manufactured by Jinshengyang Company has the characteristics of high isolation, high precision&linearity, high reliability, and low temperature drift, which can effectively isolate interference signals, transmit signals, and improve the stability and reliability of system operation.