**I. Overview**
Batteries play a crucial role in critical power systems such as Uninterruptible Power Supply (UPS), Emergency Power Supply (EPS), and DC control panels. These systems are widely used across various industries, including manufacturing, telecommunications, railways, banking, aviation, and military sectors. The performance of batteries directly impacts the reliability and stability of these power systems, making their proper selection and maintenance essential for ensuring continuous operation.
**II. Meaning and Classification**
A battery is a device that converts chemical energy into direct current (DC) and can be recharged after being discharged. Common types include lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion batteries. Among these, lead-acid batteries are commonly used in UPS and EPS systems, particularly the maintenance-free type. As one of the most vulnerable components in these systems, the lifespan of a battery depends heavily on correct usage and maintenance. Improper handling can significantly reduce its life, leading to early failure and potential losses for users.
Battery types are generally categorized based on purpose, charge state, and structure:
1. **By Purpose**:
- Starting batteries: Designed for high-current discharge, often used in vehicles and engines.
- Fixed batteries: Used for backup power in power plants, hospitals, and communication systems.
- Traction batteries: Used in electric vehicles and forklifts requiring high capacity and durability.
- Other specialized uses: Varying sizes and capacities depending on specific needs.
2. **By Charge State**:
- Dry-charged: Plates are in a discharged state without electrolyte, requiring initial charging before use.
- Dry: No electrolyte present, ready for immediate use.
- Wet: Fully charged with electrolyte, no need for initial charge.
- Maintenance-free: Requires no water addition during its service life.
- Low-maintenance: Needs minimal water topping up over time.
3. **By Structure**:
- Open type: Allows gas to escape freely but is now obsolete due to acid mist issues.
- Sealed type: Prevents acid mist from escaping, with safety valves to release excess pressure.
- Acid-proof and explosion-proof: Designed to prevent fire or explosion under extreme conditions.
- Valve-regulated sealed: Completely sealed, with automatic pressure release, ideal for modern applications.
**III. Use of Lead-Acid Batteries**
Lead-acid batteries consist of lead electrodes and sulfuric acid electrolyte. They have been in use since 1859 and are known for their reliability. Their capacity is measured in ampere-hours (Ah), calculated by multiplying the number of positive plates by the capacity of each plate.
In UPS and EPS systems, maintenance-free lead-acid batteries are commonly used, such as brands like German Sun, GNB, Yuasa, Zhicheng Champion, Panasonic, and Hercules. Users should avoid low-quality batteries, as they may compromise system reliability and cause greater damage.
Before using a maintenance-free battery, it's important to check its open-circuit voltage. If it drops below 12V, it needs extended charging. Regular checks for oxidation, cleanliness, and secure connections are also recommended.
During operation, maintenance-free batteries should be monitored for signs of swelling, leakage, or abnormal temperature. An online monitoring system can help track voltage, internal resistance, and temperature changes for early detection of issues.
Proper installation, temperature control, and charging practices are key to extending battery life. Charging methods include initial, normal, and equalization charging. Floating charge is particularly important in power systems, where the float voltage must be carefully set—typically around 2.23V per cell—to avoid overcharging or undercharging.
Discharge should be controlled to avoid deep discharges, which can reduce cycle life. Regular testing and periodic discharges help maintain battery health. Deep discharge should be avoided at all costs.
**IV. Failure Mechanisms of Lead-Acid Batteries**
Common failures include water loss, negative plate sulfation, positive plate corrosion, and thermal runaway. Water loss increases electrolyte density, leading to grid corrosion and reduced capacity. Sulfation occurs when the battery isn't fully charged, reducing active material and gas absorption capability. Thermal runaway, caused by excessive charging voltage, leads to overheating, bulging, and eventual failure.
Valve-regulated lead-acid batteries (VRLA) are designed to minimize water loss through oxygen recombination. However, they require strict charging parameters to prevent overcharging and thermal issues.
**V. Conclusion**
Lead-acid batteries, especially maintenance-free types, are vital in modern power systems. Proper understanding, usage, and maintenance can significantly extend their life, ensuring reliable power backup and maximizing benefits for businesses. Always choose quality batteries and follow manufacturer guidelines to avoid costly failures.
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