How should engineers deal with the DC high voltage in the detection of small lead-acid battery cell shells?

1. Introduction

With the continuous improvement of the quality of lead-acid batteries, their application scope is becoming more and more extensive. To produce a qualified lead-acid battery, it must go through multiple production processes, and each production process has strict process requirements. At present, most battery shell manufacturers only rely on manual inspection of the injection molding effect after the battery cell shell is injected to remove unqualified products. In the process of cell shell injection molding, affected by factors such as temperature and material, the cell shell may have defects such as pores and hair. Since the partitions connecting the cells of the cell shell of small-density lead-acid batteries are thinner than those of medium- and large-density batteries, and the spacing between the cells of small-density batteries is also smaller, it is difficult to find certain defects of the cell shell by manual inspection alone. It is too late to remove the unqualified products caused by this by the detection instrument when the semi-finished battery is produced, and a lot of manpower and material resources have been wasted. In response to this situation, we refer to the high-voltage detection principle of relevant foreign finished battery tightness detection equipment, and successfully developed a high-quality and low-cost cell shell detection machine. It is suitable for the detection of various large, medium and small lead-acid battery cell shells, and is particularly valuable for the promotion of small lead-acid batteries.

2. Detection principle

Two thick copper plates are placed close to the partitions on both sides of the partition of the injection-molded battery cell shell. One of the copper plates is connected to the DC high voltage, and the other copper plate is connected to the ground wire. A DC high voltage of 15,000 volts to 30,000 volts is added between the two copper plates. The leakage current is detected to judge the quality of the cell shell. When the cell shell partition has pores or hair defects, the partition becomes thinner, the ability to withstand high voltage is poor, the air is severely ionized, and the leakage current is significantly larger than that of the normal cell shell. When the detected leakage current is greater than the set leakage current, we use sound and light alarms to indicate that the battery is unqualified. (The set leakage current value is determined according to the actual situation). Take a 12V6-cell small lead-acid battery as an example, the high-voltage connection of its cell shell is shown in Figure 1.


3. Composition of the main circuit

The key to the battery shell detection machine for battery shell detection is the generation of DC high voltage. Its main circuit is shown in Figure 2.


In the figure, TM1 is a voltage regulator, and TM2 is a high-voltage transformer. The high voltage generated by TM2 is rectified by the high-voltage diode D1 to obtain a DC high voltage of 0 to 30,000 volts (peak voltage ). The high-voltage resistors R1 and R2 are current-limiting resistors. We use the voltmeter V to indirectly indicate the actual high voltage value, that is, the low voltage of the primary of the high-voltage transformer TM1 is sent to the voltmeter, and the voltage value indicated on the meter head is the high voltage value converted according to the primary and secondary relationship of the high-voltage transformer. This treatment can save costs and ensure safety. This device sends the voltage at point P21 to another comparison link. This voltage is compared with the set leakage current to control whether to sound and light alarm, so as to eliminate unqualified products. Since the material of the battery shell is slightly different and the air humidity also changes, various factors may cause a slight change in the voltage at point P21 in the case of a qualified battery shell. This change is enough to cause the device to misjudge. In order to solve this problem, we have connected different resistors in series in the main circuit (in the dotted box) to make a choice by adjusting the knob SA to offset various influences and avoid misjudgment of the equipment. 4. Insulation of DC high voltage, high voltage resistance of components and high voltage safety. The principle of DC high voltage generation is not complicated. The key to this equipment lies in several other aspects . The first is the insulation of high voltage. If the insulation of high voltage is not handled properly, it will not only affect the normal operation of the equipment, but also pose a great threat to personal safety. The second is the problem of high voltage resistance of components. If the selection of components does not meet the requirements, the equipment will not meet the user's requirements for long-term operation. In addition, because high voltage is dangerous to people, we should pay special attention to the safe handling of high voltage. We have done a lot of meticulous work around the above issues. We cast the high-voltage transformer with vacuum epoxy resin and carried out strict high-voltage insulation tests on the high-voltage transformer. Although the rated current of the main circuit is small, the rated withstand voltage is 1.5 to 2 times the actual high voltage, so all the wires passing through the high voltage use high-voltage wires with a rated withstand voltage of 1.5 to 2 times the actual voltage. In the connection of the wires, we separate the low-voltage circuit from the high-voltage circuit and fully consider the direction of the wire routing. The installation of high-voltage components is also completely separated from the installation of low-voltage control devices, which can prevent the interference of high-voltage magnetic fields on the low-voltage control system and increase the safety of the equipment. We have done a lot of technical consulting work on the installation carrier of high-voltage components. We use high-voltage resistant and inexpensive PP boards to make boxes. High-voltage components are installed in PP board boxes. To prevent high-voltage air ionization and sharp corner discharge, we isolate the high-voltage components from each other. In order to ensure the safety of the equipment, this equipment fully considers the safety treatment of high voltage without exposure and grounding, and meets the higher requirements for equipment use. 5. Conclusion This equipment has been used by users for more than half a year. The whole machine runs stably and reliably, with fast detection speed and accurate judgment. The user feedback is good. This product can reduce the labor intensity of workers, improve product quality and production efficiency, and has a high promotion value in the production of small-density lead-acid batteries.