How to Build a 24V 20Ah Lithium-Ion Battery Pack: A Step-by-Step Guide

Creating a lithium-ion battery pack at home can be a rewarding project, whether you're looking to power tools, an electric bike, or an off-grid setup. In this article, we’ll walk you through the process of building a 24V 20Ah lithium-ion battery pack. We'll cover the basics of battery specifications, connection types, and safety measures while providing a detailed guide for assembly.


Why Choose Lithium-Ion Batteries?

Before diving into the steps, let’s quickly review the benefits of lithium-ion batteries:

  1. Faster Charging: Lithium-ion batteries charge much faster compared to lead-acid batteries.
  2. Better Backup: They provide longer backup durations with consistent performance.
  3. Low Maintenance: With proper charge and discharge cycles, they can last up to 5 years or more.

Step 1: Understanding Your Requirements

The first step in building a battery pack is determining your voltage and capacity (Ah) requirements. For this guide, we are building a 24V 20Ah battery pack.

Key Concepts: Voltage and Capacity

  • Voltage (V): Determines the power output of the battery pack. For example, we are targeting 24V.
  • Capacity (Ah): Determines how long the battery will last. For example, 20Ah means the battery can deliver 20 amps for one hour.

Step 2: Selecting the Cells

Lithium-ion batteries come in various capacities, such as 1200mAh, 2000mAh, 2600mAh, and 3000mAh. For this project, we’ll use 2500mAh cells from Winway, known for their high quality and low internal resistance (IR value: 20mΩ).

Calculation for Total Capacity:

  • Each cell: 3.7V, 2500mAh.
  • For 24V, connect 7 cells in series to achieve the voltage.
  • For 20Ah capacity, connect 8 such series in parallel.

Connection Types

  1. Series Connection: Increases the voltage. Connect the positive terminal of one cell to the negative terminal of the next.
  2. Parallel Connection: Increases the capacity. Connect the positive terminals together and the negative terminals together.

Step 3: Required Materials

Here’s what you’ll need:

  • Lithium-ion cells (3.7V, 2500mAh): 56 cells (7 in series × 8 in parallel).
  • Battery spacers: For arranging cells.
  • Nickel strips: For connecting the cells.
  • BMS (Battery Management System): Use a high-quality DALY BMS for overcharge and over-discharge protection.
  • Spot welder: For connecting nickel strips (or a 60W soldering iron as an alternative).
  • Epoxy sheets: For casing.
  • Heat shrink wrap: For insulation and final finishing.

Step 4: Assembly Process

Step 4.1: Preparing the Cells

  1. Label Positive Terminals: Use stickers or paper tape to avoid short circuits since the battery body is usually negative.
  2. Arrange Cells: Use battery spacers to arrange the cells in a 7×8 block. If spacers are unavailable, you can use hot glue.

Step 4.2: Connecting the Cells

  1. Spot Welding: Cut nickel strips and weld them across the cells to form series and parallel connections.
    • For series: Connect the positive of one cell to the negative of the next.
    • For parallel: Connect all positives together and all negatives together.
  2. Check Voltage: After connecting, use a multimeter to ensure the voltage matches your requirements (around 24V).

Step 5: Adding the Battery Management System (BMS)

Why Use a BMS?

A BMS ensures:

  • Equal charging of all cells.
  • Protection from overcharging and over-discharging.
  • Prevention of overheating and potential damage.

Steps to Install the BMS:

  1. Connect the Wires: Follow the wiring diagram provided by the BMS manufacturer.
  2. Solder the Connections: Ensure tight and secure connections to avoid power loss or malfunction.
  3. Check the System: After wiring, verify with a multimeter to ensure all cells are charging equally.

Step 6: Final Assembly

  1. Casing: Use epoxy sheets to create a durable and protective box around the battery pack.
  2. Insulation: Cover the battery pack with heat shrink wrap for added protection and a professional finish.

Step 7: Testing the Battery Pack

  1. Voltage Check: Use a multimeter to confirm the voltage is around 24V.
  2. Load Testing: Connect the pack to a device or load and monitor its performance.
  3. App Connection: If using a smart BMS, connect it to the app for real-time monitoring.

Circuit Diagram

(Add a detailed and labeled circuit diagram here for reference.)


Tips for Success

  • Use High-Quality Components: This includes cells, BMS, and nickel strips.
  • Safety First: Avoid short circuits, and ensure proper insulation to prevent hazards.
  • Pro Tip: If spot welding is unavailable, scratch the cell terminals before soldering for better adhesion.

Order Ready-Made Battery Packs

If you prefer not to build one yourself, you can order a ready-made battery pack from our WhatsApp store. Simply provide your voltage and capacity requirements. Note: Only prepaid orders are accepted.


Conclusion

Building a 24V 20Ah lithium-ion battery pack may seem complex, but with the right materials and guidance, it’s entirely achievable. Follow the steps outlined above, and you’ll have a powerful and efficient battery pack for your needs.

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