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1.The serious consequences of short circuit of lead-acid battery

Lead-acid batteries play a key role in the energy system of modern society, and are widely used in automotive start-up, backup power supply of communication base stations, emergency lighting and other fields. However, the hidden danger of short circuit is like a "time bomb" lurking in the dark, which always threatens its safe and stable operation. Once a short circuit occurs, a huge current will pass through the battery. According to Ohm's law I=U/R (where I is the current, U is the electromotive force of the battery, R is the short-circuit resistance, and R is close to zero when the short circuit), the large current will cause the battery to heat up sharply, resulting in the rapid heating of the battery shell, and even softening and deformation, and the internal plate is damaged. In severe cases, the high temperature generated by the short circuit may ignite the combustible gas inside the battery, causing an explosion, which will not only cause the battery itself to be scrapped, but also may pose a serious threat to the safety of surrounding equipment and personnel. For example, in the car, the battery short circuit may cause the vehicle to suddenly stall, the circuit system burned, if it occurs during the driving process, it is easy to cause traffic accidents; The short circuit of the lead-acid battery of the communication base station will cause the failure of the backup power supply, resulting in communication interruption and affecting the communication service in a large area.

2. The source of the hidden danger of short circuit at the line design level

a. Improper wiring

In the circuit design stage of lead-acid battery system, unreasonable wiring is a common factor that causes short circuit. When cables with different voltage levels and different functions are not effectively isolated and are laid in parallel at a close distance, electromagnetic induction interference is likely to occur. For example, if the power cable and the control cable are parallel, the magnetic field generated by the large current of the power cable will induce abnormal voltage in the control cable. If the insulation layer of the control cable is weak, a breakdown and short circuit may occur. In addition, the cable bending radius is too small will also lay hidden dangers. If a lead-acid battery cable is bent excessively, the conductor inside the cable may be broken or partially broken. The sharp part of the broken cable may puncture the insulation layer and contact the adjacent conductor, resulting in short circuit. For example, battery pack wiring in some compact Spaces bends the cable excessively to accommodate the space, increasing the risk of short circuit.

b. Improper component selection

The selection of various electrical components in the line is very important to prevent short circuits. As a key component of short-circuit protection, if the rated current is too large, when the circuit is short-circuited, the fuse cannot fuse and cut off the circuit in time, and the short-circuit current will continue to exist, causing damage to the battery and the line. On the contrary, if the rated current is selected too small, the normal working current may also cause the fuse to misoperate, affecting the normal operation of the system. For example, in an automobile starting system, the instantaneous starting current is large, and if the rated current of the fuse is set improperly, it may lead to startup failure or failure to effectively protect the circuit. In addition, the contact quality of relays, contactors and other switching components is poor, and it is easy to produce arc in the frequent opening and closing process, which may abate the contact and cause short circuit. If the design is not based on the actual load current and frequency of use to select the appropriate high-quality switching components, it will create conditions for short circuit hazards.

c. Insulation design defect

Insulation is the first line of defense against short circuit, and insulation design defects can make this line of defense useless. In the selection of insulating materials for battery connection lines, if the use of the environment is not fully considered, such as in high temperature, humidity or chemical corrosion environment, the selection of insulation materials that are not high temperature resistant, not waterproof or poor corrosion resistance, over time, the insulation layer will gradually age and damage. For example, in outdoor communication base stations, the battery line is exposed to the sun and rain for a long time, and the cable skin made of ordinary insulation materials is easy to crack, causing short circuit after water intrusion. In addition, the thickness of the insulation layer is insufficient to withstand the normal operating voltage and the possible instantaneous overvoltage impact, which will also lead to insulation breakdown and short circuit fault.

3. Troubleshooting points of short circuit hidden dangers in daily maintenance

a. Regular appearance inspection

During routine maintenance, regular appearance inspection of lead-acid batteries and their connecting lines is the basic work to detect potential short circuits. Check whether the battery shell is deformed, bulging or cracked. If these conditions exist, it may mean that the battery has a short circuit or the risk of a short circuit, because the high temperature and high pressure generated by the short circuit will damage the battery shell. At the same time, carefully check whether the outer cover of the cable is damaged, scratched, aging and cracking, and whether the cable joints are loose, corroded, or ablated. For example, if there are obvious scratches on the outer cover of a cable, the internal insulation layer may be damaged. If there is green or white corrosion on the joint, it indicates that there may be electrolyte leakage, which may cause poor contact or even short circuit. Clean and tighten the joint in time.

b. Electrical parameter detection

The use of professional instruments to detect the electrical parameters of the battery and the line can accurately detect the hidden dangers of short circuit. Use a multimeter to periodically measure the open circuit voltage, charge and discharge voltage, and current of the battery. If the battery voltage is abnormally low, and other factors (such as aging and insufficient charging of the battery) are excluded, there may be an internal short circuit. For example, the open circuit voltage of a normally fully charged lead-acid battery should be about 12.6V (12V battery). If the measured value is significantly lower than this, in-depth inspection is required. In addition, the line current is measured by the clamp ammeter. If the current value is much higher than the normal range under the normal operation of the equipment, there may be a short circuit resulting in an increase in the current. At the same time, you can also use the insulation resistance tester to detect the insulation resistance of the line. Generally, the insulation resistance value should be at the megHM level. If the resistance value is too low, it indicates that the insulation performance is reduced and there is a risk of short circuit.

c. Cleaning and protective maintenance

Keeping the lead-acid battery and its surrounding environment clean is an important link to prevent short circuit. If a large amount of dust and debris is accumulated on the battery surface, especially in a humid environment, the dust and debris can easily absorb water and form a conductive path, resulting in short circuit between the positive and negative electrodes of the battery. Therefore, periodically wipe the battery surface with a clean, damp cloth, avoiding dry cloth that may generate static electricity. At the same time, check whether the protective facilities in the battery room or equipment are in good condition, such as fire, water and moisture proofing measures. Lay insulation pads on the floor of the battery room to prevent personnel from accidentally touching short circuit; Ensure that the ventilation is good to avoid the accumulation of combustible gas generated by the battery to cause an explosion. In addition, for batteries used outdoors, it is necessary to check whether the protective shell is well sealed to prevent rain, sand and dust from entering, damaging the line insulation layer and causing short circuit failure.

The hidden danger of short circuit of lead-acid battery is related to the safety of equipment and the stable operation of the system, from the source control of line design to the careful investigation in daily maintenance, each link can not be ignored. Reasonable circuit design, appropriate component selection and perfect insulation design can reduce the risk of short circuit. Regular appearance inspection, accurate electrical parameter detection, and effective cleaning and protective maintenance can detect and eliminate potential short circuit hazards in time. Only by closely combining line design and daily maintenance, and doing a full range of short-circuit troubleshooting of lead-acid batteries, can they ensure safe and reliable operation in various application scenarios.