Building a 12v 30Ah Lithium Battery Pack – Step by Step!

Building an 4S (4 series) LiFePO4 battery pack using 32140 LiFePO4 cells and a Daly Battery Management System (BMS). If you’re planning your own DIY power storage project, this guide might help you get started!

Why LiFePO4?

Lithium Iron Phosphate (LiFePO4) batteries have gained popularity for their safety, long lifespan, and thermal stability. Compared to standard lithium-ion batteries, LiFePO4 cells can handle more charge cycles (2000-5000), making them perfect for applications like solar storage, electric vehicles, and DIY backup systems.

Components I Used:

• 20 x 32700 LiFePO4 Cells (3.2V nominal, 12-15Ah each)
• Daly 4s BMS (12v rated, with balancing and protection features)
• Nickel strips for cell interconnection
• Spot welder
• XT60 connectors
• Heat shrink tubing
• Multimeter and basic tools

What Is BMS?

A BMS stands for Battery Management System. It’s an electronic system that manages and protects rechargeable batteries — especially in packs like your LiFePO4 8S setup.

Key functions of a BMS:

• ✅ Overcharge protection (prevents damage from too high voltage)
• ✅ Over-discharge protection (prevents deep discharge that can ruin cells)
• ✅ Short-circuit protection (cuts off power in case of a fault)
• ✅ Cell balancing (keeps all cells at the same voltage to extend lifespan)
• ✅ Temperature monitoring (some advanced BMSs monitor heat to avoid thermal issues)

Configuration: 4S

• 4S means 4 cells connected in series.
• Each LiFePO4 cell = 3.2V nominal.
• So, 4 x 3.2V = 12.8 v nominal (and about 14v when fully charged).

This makes it suitable for 12v systems like solar inverters, e-bikes, and portable power stations.

Circuit Diagram:

Assembly Steps:

1. Planning the Layout
   • I arranged the 4 cells in a straight line to keep the design compact.
2. Spot Welding the Cells
   • Used nickel strips and a spot welder to connect the cells in series.
   • Double-checked the polarity and voltages after each connection.
3. Connecting the Daly 8S BMS
   • The Daly BMS is the brain of the battery, providing overcharge, over-discharge, and short-circuit protection.
   • Connected the balance leads to each cell, following the 4S wiring diagram provided by Daly.
4. Final Checks
   • Measured total pack voltage (should be around 13.0 V).
   • Checked individual cell voltages for balance.
5. Wrapping and Finishing
   • Wrapped the pack with heat shrink for insulation and added XT60 connectors for easy connection.

Testing the Pack:

Once assembled, I tested the pack with a 12v inverter and a small load. The Daly BMS handled the balancing and protection well, and the pack performed smoothly. I monitored the temperatures and voltage during the first few charge/discharge cycles.

Applications:

• Solar energy storage
• DIY powerwall projects
• Portable battery backup
• E-bikes and scooters

Tips for Builders:

• Always double-check BMS wiring—it’s the most critical part!
• Use proper insulation to avoid shorts.
• Don’t skip balance charging during the initial setup.

DALY BMS:

The Daly K-Series Smart BMS is a powerful and intelligent Battery Management System designed for lithium iron phosphate (LiFePO₄) and lithium-ion batteries. It supports 3S to 24S configurations and is available in 40A, 60A, and 100A versions, making it ideal for a wide range of applications including electric vehicles, solar energy storage, and backup power systems.

With built-in communication options like CAN, RS485, and UART, users can monitor and adjust settings in real time via a mobile app or PC software.

Everything You Need to Know About the 32700 LiFePO4 (LFP) Battery Cell

In the ever-evolving world of energy storage, LiFePO4 (Lithium Iron Phosphate) batteries are becoming a top choice for both hobbyists and large-scale applications. One of the most popular formats in this category is the 32700 cell — a cylindrical, high-capacity, and long-lasting battery that is gaining attention in DIY solar systems, electric vehicles, power banks, and more.

What is a 32700 LiFePO4 Cell?

The name 32700 refers to the cell’s dimensions:

32 mm diameter

70 mm length

It’s similar in shape to the common 18650 cell, but significantly larger and more powerful. When you combine this with the LiFePO4 chemistry, it becomes a robust and safe energy storage solution.

Typical Specifications:

Nominal Voltage: 3.2V

Capacity: 6000 mAh to 7000 mAh (varies by manufacturer)

Standard Charging Current: 0.5C to 1C

Max Discharge Current: 3C or higher (20A+ in some models)

Cycle Life: 2000 to 5000+ cycles

Operating Temp: –20°C to 60°C (ideal for harsh environments)

LiFePO4 cells like the 32700 offer several advantages:

✅ Long Life: 4x more cycles than traditional Li-ion (NMC) cells.

✅ Thermal Stability: Safer under high temperatures; lower fire risk.

✅ Flat Discharge Curve: Voltage remains stable even under heavy loads.

✅ Eco-Friendly: Free from cobalt and other toxic metals.

Applications of 32700 LFP Cells

Because of their excellent performance and safety, these cells are used in:

🌞 Solar Power Storage (home & portable systems)

🚲 Electric Bikes & Scooters

🔋 DIY Power Banks & Backup Systems

🧰 Battery Packs for Tools or Robots

🌍 Off-grid Power Solutions

You’ll often find them in 8S or 16S configurations in solar inverters, replacing bulky lead-acid batteries with lighter, longer-lasting packs.

More Projects