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Views: 0 Author: Site Editor Publish Time: 2025-10-13 Origin: Site
When a single lithium battery cell doesn't meet your project's voltage or capacity requirements, the solution is to combine multiple cells. This is done through two fundamental configurations: **series** and **parallel**. Understanding the difference between them is crucial for designing safe and effective battery packs for applications like electric vehicles, solar energy storage, or portable power stations.
Let's break down how each connection works and what it accomplishes.
#### **The Core Concept: Voltage vs. Capacity (Ah)**
To understand the difference, remember these two key principles:
* **Series Connections** increase **Voltage (V)**.
* **Parallel Connections** increase **Capacity (Amp-hours, Ah)**.
Think of electricity like water in a tank:
* **Voltage** is like water *pressure*.
* **Capacity (Ah)** is like the *size* or *volume* of the tank.
#### **Battery in Series: Boosting the Voltage**
In a series connection, you connect the positive terminal of one cell to the negative terminal of the next.
* **How it works:** The voltages of each cell add together.
* **Formula:** `Total Voltage = Cell Voltage × Number of Cells`
* **Capacity:** The total capacity (in Amp-hours) remains the **same** as a single cell.
* **Analogy:** Connecting batteries in series is like stacking several small water tanks on top of each other. The water pressure (voltage) at the bottom increases, but the total amount of water (capacity) doesn't change.
**Example:**
If you connect four (4) 3.7V, 5Ah lithium cells in series:
* **Total Voltage:** 3.7V × 4 = **14.8V**
* **Total Capacity:** Remains **5Ah**
This configuration is ideal for devices that require a higher operating voltage.
#### **Battery in Parallel: Boosting the Capacity**
In a parallel connection, you connect all the positive terminals together and all the negative terminals together.
* **How it works:** The capacities of each cell add together.
* **Formula:** `Total Capacity = Cell Capacity × Number of Cells`
* **Voltage:** The total voltage remains the **same** as a single cell.
* **Analogy:** Connecting batteries in parallel is like placing several water tanks side-by-side and connecting them at the bottom. The water pressure (voltage) stays the same, but the total amount of water (capacity) you can store increases significantly.
**Example:**
If you connect four (4) 3.7V, 5Ah lithium cells in parallel:
* **Total Voltage:** Remains **3.7V**
* **Total Capacity:** 5Ah × 4 = **20Ah**
This configuration is perfect for applications that need to run for a longer time on a single charge.
#### **Series-Parallel Combinations: The Best of Both Worlds**
For most high-power applications, you need both higher voltage *and* higher capacity. This is achieved by creating a **Series-Parallel** battery pack.
This involves creating several series strings to achieve the desired voltage and then connecting those strings in parallel to increase the capacity.
**Example:**
To create a 7.4V, 10Ah pack from 3.7V, 5Ah cells:
1. **Create Series Strings:** First, make two strings of two cells in series.
* Each string: 3.7V × 2 = **7.4V**, Capacity = **5Ah**
2. **Connect Strings in Parallel:** Then, connect these two 7.4V strings in parallel.
* Total Voltage: Remains **7.4V**
* Total Capacity: 5Ah + 5Ah = **10Ah**
#### **Critical Considerations for Safety and Performance**
Simply connecting cells is not enough. For a safe and long-lasting pack, you must consider:
1. **Matching Cells:** Always use cells of the **same chemistry, voltage, capacity, and age.** Mismatched cells can lead to imbalanced charging, reduced performance, and safety hazards.
2. **Battery Management System (BMS):** A BMS is absolutely essential, especially for series and series-parallel packs. It:
* **Monitors Individual Cell Voltages** (crucial in series).
* **Prevents Overcharging and Over-discharging.**
* **Provides Cell Balancing** to ensure all cells in a series string charge and discharge evenly.
* **Protects against overcurrent and short circuits.**
#### **Summary: Key Differences at a Glance**
| Feature | Series Connection | Parallel Connection |
| :--- | :--- | :--- |
| **Voltage** | **Increases** (adds up) | **Stays the same** |
| **Capacity (Ah)** | **Stays the same** | **Increases** (adds up) |
| **Purpose** | Power high-voltage devices | Extend runtime |
| **Critical Need** | **Cell Balancing** (via BMS) | **Matched Cells** to avoid cross-currents |
**Conclusion**
Understanding series and parallel connections is the foundation of building any custom lithium battery pack. Series gives you the "push" (voltage), while parallel gives you the "endurance" (capacity). By combining them thoughtfully and always incorporating a robust BMS and properly matched cells, you can create a power source that is perfectly tailored to your specific needs, all while ensuring safety and reliability.
