In modern power systems, Uninterruptible Power Supplies (UPS) play a crucial role. They can provide reliable backup power when the mains power fails, ensuring the continuous operation of critical equipment such as servers, medical instruments, and communication systems. One of the core components of a UPS is its battery pack, which is connected in ingenious ways to meet different power requirements and runtime demands. Among these, series and parallel connections of battery packs are two common configuration methods: series connection is mainly used to increase voltage, while parallel connection is used to enhance capacity, thus adapting to various application scenarios. This article will elaborate on the principles, advantages, and precautions of these connection methods in detail to help you better understand and apply UPS systems.

UPS Battery Pack Series Connection: Increasing Voltage to Meet High-Power Demands

Series connection of battery packs refers to connecting the positive terminal of one battery to the negative terminal of the next battery in sequence, forming a chain structure. In this configuration, the total voltage is equal to the sum of the voltages of individual batteries, while the capacity (measured in Ampere-hours, Ah) remains unchanged. For example, if four 12V, 100Ah batteries are connected in series, the total voltage will reach 48V, but the capacity will still be 100Ah. This method is similar to series resistors in a circuit, where voltages add up and the current path is single.

The advantage of series connection lies in its ability to easily achieve higher output voltage, which is particularly important for UPS systems requiring high power. In large data centers or industrial environments, high voltage can reduce current loss, improve transmission efficiency, and support higher-power loads. According to relevant data, the principle formula for series connection is: Total Voltage V_total = V1 + V2 + ... + Vn, where the voltages of individual batteries are added together, and the capacity is determined by the smallest battery in the series. This makes series configuration especially suitable for UPS applications with strict voltage requirements, such as medium and high-voltage UPS systems.

In practical applications, series battery packs are often used to expand the power output of UPS. For instance, in a system requiring 48V DC output, the target voltage can be achieved by connecting four 12V batteries in series, thereby meeting the power needs of higher-power equipment. However, it should be noted that series connection amplifies the weaknesses of individual batteries—if one battery fails, the performance of the entire chain will be affected.

UPS Battery Pack Parallel Connection: Enhancing Capacity to Extend Runtime

In contrast to series connection, parallel connection involves connecting the positive terminals of all batteries together and the negative terminals of all batteries together. This configuration keeps the total voltage unchanged but adds up the capacities, thereby providing greater current output and longer backup runtime. For example, if four 12V, 100Ah batteries are connected in parallel, the total voltage remains 12V, but the capacity increases to 400Ah. This is similar to parallel resistors in a circuit, where total capacity is enhanced while voltage remains stable.

The advantage of parallel connection is that it significantly extends the runtime of UPS, which is especially suitable for scenarios with high requirements for backup duration, such as emergency power systems in hospitals or financial centers. According to online data, parallel connection can reduce internal resistance, extend power supply time, and improve system redundancy. In addition, parallel connection can balance the load—when one battery pack is depleted, other packs can continue to supply power, thereby enhancing overall reliability.

In UPS design, parallel connection is often used for capacity expansion. For example, some UPS systems allow multiple battery packs to be connected in parallel to support longer power failure protection time. However, not all UPS systems support unlimited parallel connection, as this is limited by the system architecture and the capacity of the charger. This makes parallel connection a flexible option for meeting different runtime requirements.

Series-Parallel Combination: Comprehensive Optimization of Power and Capacity

In practical engineering, series and parallel connections are often used in combination to form a series-parallel hybrid configuration. This method can both increase voltage and enhance capacity, meeting complex requirements. For example, batteries are first divided into groups and connected in series to increase voltage, and then these groups are connected in parallel to enhance capacity. The final output can be a combination of high voltage and high capacity, such as a 48V, 400Ah system.

The advantages of this hybrid configuration are obvious: it allows UPS systems to be custom-designed according to specific power and runtime requirements. Relevant research indicates that series-parallel connection can increase voltage, expand capacity, reduce internal resistance, and provide more stable power output. In high-availability environments such as cloud computing centers, this configuration can effectively cope with peak loads and long-term power outages.

Precautions: Ensuring Safety and Performance Consistency

Although series and parallel connections bring many benefits, improper operation may lead to safety hazards and performance degradation. The following are key precautions:

• Battery Consistency: Avoid mixing batteries of different brands, capacities, ages, or types (e.g., lead-acid batteries and lithium batteries). Inconsistent performance may cause differences in internal resistance, resulting in over-discharge or over-charging. It is recommended to select batteries with an internal resistance difference of no more than 5 milliohms and a capacity difference of no more than 10mAh.

• Protection Circuitry: Especially in lithium battery UPS systems, configure a protection board (such as a Battery Management System, BMS) to monitor the status of each battery and prevent over-voltage, over-current, and short circuits.

• Internal Resistance and Discharge Balance: Batteries with smaller internal resistance will discharge first, which may lead to imbalance. Regular inspection and balanced charging are essential.

• System Compatibility: Not all UPS systems support multiple parallel groups; it is necessary to check the charger capacity and switch box configuration. When multiple groups are connected in parallel, it is recommended to use a combiner box to evenly distribute current.

• Maintenance and Replacement: When the battery power is insufficient, all batteries should be replaced as a whole. Keep the connection points clean to avoid corrosion.

These precautions are based on industry experience and can significantly reduce the risk of failures, ensuring the long-term stable operation of UPS systems.

Conclusion

Series and parallel connections of UPS battery packs are core technologies for optimizing power supply systems: series connection increases voltage to support high-power demands, parallel connection enhances capacity to extend runtime, and combined use provides a comprehensive solution. Through reasonable configuration, enterprises can customize UPS according to specific scenarios to ensure the continuity of critical business operations. Selecting high-quality batteries and following safety specifications will maximize the advantages of these connection methods. If you are planning a UPS system, consult Daopulse professional engineers immediately for customized advice.