Batteries are fundamental to the operation of vehicles, from starting the engine to powering complex electronic systems. To achieve the necessary voltage and capacity for various automotive applications, battery cells are often connected in series and parallel configurations. This article delves into the principles of series and parallel battery connections, their implications for performance and diagnostics, and how understanding these configurations is crucial for effective car repair, particularly when considering the network for car diagnosis.
Single Cell Applications in Vehicles
While modern vehicles increasingly rely on complex battery packs, single-cell configurations still play a role, especially in auxiliary systems or older models. A single cell is the simplest battery setup, requiring no cell matching and minimal protection circuitry. Examples include small backup batteries for memory or certain sensors.
Different battery chemistries offer varying nominal voltages. For instance, lead-acid batteries, commonly used as starter batteries, provide around 2V per cell. Lithium-ion variants, increasingly prevalent in electric and hybrid vehicles, typically offer around 3.6V or higher. The choice of chemistry and configuration depends on the specific voltage and power requirements of the automotive system.
Series Connection in Automotive Battery Systems
In automotive applications demanding higher voltages, battery cells are connected in series. Figure 2 illustrates a series connection of four cells. By linking cells in series, their voltages add up while the capacity remains constant. For example, connecting six 2V lead-acid cells in series yields a 12V battery, the standard for many car electrical systems.
Figure 2: Series Connection of Four Cells (4s)
Series configurations are essential in electric vehicles (EVs) and hybrid electric vehicles (HEVs), where high voltages are needed to power the electric motors. These vehicles utilize battery packs comprising hundreds of lithium-ion cells in series to achieve operating voltages of 400V, 500V, or even higher.
However, a series connection’s performance is limited by its weakest cell. If one cell in the series string weakens or fails, it can significantly degrade the entire battery pack’s performance, leading to reduced range or power. This highlights the importance of cell matching and battery management systems (BMS) in series configurations, especially in automotive applications where reliability and longevity are critical. This consideration becomes even more vital when diagnosing issues within the car’s electrical network, as battery health directly impacts the stability and performance of various electronic control units (ECUs) and sensors connected to the network for car diagnosis, as potentially visualized in fig 14.8 if it were related to automotive network architecture.
Tapping into a Series String: Automotive Considerations
In some heavy-duty automotive equipment operating on 24V battery systems, there might be a temptation to tap into the series string to derive a 12V supply for auxiliary functions. This practice, however, is generally discouraged due to the cell imbalance it creates. Uneven loading across the battery string can lead to premature wear and reduced lifespan, particularly in lead-acid batteries, where sulfation and corrosion can be accelerated. Modern automotive designs mitigate this issue by employing DC-DC converters to generate different voltage levels from the main battery pack, ensuring balanced battery usage and optimal performance, which is crucial for the reliable operation of the entire car network and diagnostic systems.
Parallel Connection for Automotive Power
When higher current capacity or longer runtime is required in automotive applications without increasing voltage, cells are connected in parallel. Figure 4 demonstrates a parallel connection of four cells. In this configuration, the voltage remains the same, but the capacities of the cells add up. Parallel connections are often used in automotive auxiliary power systems or in applications requiring sustained current delivery.
Figure 4: Parallel Connection of Four Cells (4p)
In a parallel configuration, the failure of a single cell is less critical than in a series configuration. However, a shorted cell can pose a significant safety hazard, potentially leading to thermal runaway or fire. Automotive battery packs employing parallel connections often incorporate fuses or other protection mechanisms to isolate faulty cells and prevent cascading failures. Understanding parallel connections is also relevant in the context of car diagnostics, as issues in parallel branches can affect overall system power availability and might be detectable through network diagnostics, even if not directly visualized in fig 14.8.
Series/Parallel Connection in Modern Vehicles
For complex automotive battery systems, especially in EVs and HEVs, a combination of series and parallel connections is commonly employed. Figure 6 illustrates a series/parallel configuration. This approach provides design flexibility, allowing engineers to achieve both the desired voltage and current capacity using standard cell sizes. For example, a battery pack might consist of modules where cells are paralleled to increase capacity, and these modules are then connected in series to reach the required high voltage for the electric drivetrain.
Figure 6: Series/Parallel Connection of Four Cells (2s2p)
This series/parallel architecture is crucial for optimizing battery pack performance, safety, and lifespan in modern vehicles. Sophisticated battery management systems (BMS) are essential to monitor and control individual cells and modules within these complex configurations, ensuring balanced charging and discharging, thermal management, and fault detection. These BMS systems are integral to the vehicle’s diagnostic network, providing crucial data about battery health and performance that is essential for car diagnosis and maintenance. The network for car diagnosis, possibly depicted in fig 14.8, would likely include the BMS as a critical node for monitoring the power system.
Terminology in Automotive Battery Systems
The automotive battery industry, like the broader battery sector, uses specific terminology to describe series and parallel configurations. The convention is to specify the number of series connections first, followed by parallel connections. For example, a “2s2p” configuration indicates two cells in series, with two of these series strings connected in parallel. This standardized terminology is important for clear communication in automotive design, manufacturing, and service, especially when dealing with complex battery packs and their diagnostic systems.
Safety Devices in Automotive Battery Packs
Safety is paramount in automotive battery systems, particularly in high-voltage applications. Battery packs incorporate various safety devices to protect against overcurrent, overvoltage, overtemperature, and internal cell pressure. Positive Temperature Coefficient (PTC) switches and Charge Interrupt Devices (CID) are common safety components. While these devices enhance safety, it’s crucial to recognize that they can also fail. In large multi-cell automotive batteries, safety devices are carefully integrated into the BMS to provide layered protection and prevent thermal runaway or other hazardous conditions. The effectiveness and status of these safety devices are also monitored through the car’s diagnostic network.
Guidelines for Automotive Battery Maintenance and Diagnostics
Understanding series and parallel battery configurations is essential for automotive technicians and diagnosticians. When working with vehicle batteries, especially in EVs and HEVs, it’s crucial to:
- Maintain clean battery contacts: Corrosion and resistance at battery terminals can impede performance and affect diagnostic readings.
- Replace batteries as a set: In systems with multiple batteries, replacing them all simultaneously is often recommended to ensure balanced performance and prevent premature failure.
- Observe polarity: Correct polarity is critical in battery connections. Reversed polarity can damage components and create hazardous situations.
- Utilize diagnostic tools: Modern automotive diagnostic systems, potentially including network diagrams similar to fig 14.8, provide valuable data on battery health, cell balance, and overall system performance.
- Consider BMS data: The Battery Management System is a key source of information for diagnosing battery-related issues. Accessing and interpreting BMS data is crucial for accurate car diagnosis, especially in EVs and HEVs.
By understanding the principles of series and parallel battery connections and their implications for automotive systems, technicians can effectively diagnose and repair battery-related issues, ensuring vehicle safety and performance. The network for car diagnosis, including battery system monitoring, is an indispensable tool in this process.
References
[1] Courtesy of Cadex
