Foreword: The flaw detector is a portable industrial non-destructive flaw detection instrument, which can quickly, conveniently, without damage, and accurately detect, locate and evaluate various defects (welds, cracks, inclusions, folds, pores, blisters, etc.) inside the workpiece And diagnosis, can be used in the laboratory, can also be used in the engineering site. The instrument can be widely used in fields that require defect detection and quality control, such as manufacturing, steel and metallurgy, metal processing, and chemical industries. It is also widely used in in-service safety inspections and in areas such as aerospace, railway transportation, boilers and pressure vessels, etc. Life assessment, it is a must in the non-destructive testing industry. Portable flaw detectors have become an important tool for on-site testing in modern society, and providing portable flaw detectors with efficient, portable, lightweight, and sufficient backup power solutions is an important guarantee for testers to carry out long-term on-site work. The 18650 lithium battery pack has become the first choice for this type of high-tech test instrument backup power solution due to its own unique advantages.
1. Design requirements of spare lithium battery for flaw detector:
Due to the characteristics of high voltage and long working time of the flaw detector, the quality of the equipment itself and the continuous stability of the power supply are particularly critical. This requires that its power supply must be realized by the multiple series and parallel combination of large-capacity single lithium batteries; During the work process, a large amount of valuable data needs to be kept continuously. Therefore, an accurate battery power display and alarm system must be provided to remind the user to save the data in time to improve the effectiveness of the work. This flaw detector's backup lithium battery solution uses an intelligent chip. The host continuously reads the power and related important data in the smart chip through I2C communication, and monitors the battery from time to time to remind the user to perform related operations in a reasonable and timely manner. The Sanyo batteries integrated in our solution have the advantages of high energy ratio, light weight, small size, high cycle life, high safety, high voltage, and good consistency. The lithium battery pack is designed to output an overcurrent protection value of 12A and continuous working current. 7A, charge capacity 5000mAh, fully meet the power demand of the instrument. The specific design requirements are as follows:
1) Lithium battery pack model design requirements: 18650-3S2P/5000mAh/11.1V.
2) Design requirements for the circuit part:
1. Single cell overcharge protection voltage: 4.35± 0.25V
2. Single cell overcharge recovery voltage: 4.15±0.50V
3. Single cell over-discharge protection voltage: 2.40±0.08V
4. Single cell over-discharge recovery voltage: 3.00±0.10V
5. Combined battery overcurrent protection value (10ms): 30~35A
6. Combined battery over-temperature protection value (recoverable): 70±5℃
7. The finished battery also has short circuit and reverse charge protection.
3) Design requirements for battery cycle life: 300~500 times (national standard charge and discharge standards)
4) Design requirements for battery dimensions: refer to battery housing
2. Design scheme of spare lithium battery for flaw detector:
1) Smart fuel gauge protection board (PCM): Adopt SBS smart battery management system, use advanced power calculation principle to accurately calculate the battery power from time to time, and report the battery power information to the host from time to time through SMBUS, and at the same time to the rechargeable smart battery The group performs functional protection. Due to the chemical characteristics of the lithium battery itself, it is necessary to provide protection functions such as overcharge, overdischarge, short circuit, overcurrent, and overtemperature to avoid burning, explosion and other hazards.
2) 18650 lithium ion battery cell/18650/2500mAh/3.7V Li-ion cell (SANYO).
3) Temperature switch: Mainly designed for temperature protection function. When the temperature of the battery itself reaches the range of 70±5°C due to other abnormal problems, the temperature switch will act to perform temperature protection.
4) Field effect tube (MOSFET): MOSFET, which acts as a switch in the protection circuit, will always keep the voltage at both ends of the load from increasing or decreasing, ensuring voltage stability.
5) Battery pack packaging (housing)