Introduction: How to Assemble a 24V 120Ah LiFePO4 Battery With BMS?

By QH Technology
About: We want to lighten the world💡💡--LiFePO4 batteries for energy storage(#solarenergy, RVs, Golf Carts, Forklifts, etc.)

Lithium iron phosphate batteries can be roughly divided into 12V, 24V, 48V, and high voltage. The 25.6V 120Ah is ideal for ships, electric vehicles, UPS, communication base stations, and other equipment to provide continuous power. BMS, Battery Management System, is a mandatory component for LiFePO4 batteries, which can prevent the battery pack from over-charging, over-voltage, and over-current.

Some DIY enthusiasts are interested to build their own battery pack. Not only can they practice their electrical skills, but also obtain a LiFePO4 battery pack at a lower price.

There are a lot of advantages of LiFePO4 battery 24V. With a 5,000-time deep cycle and a wide temperature range, the 25.6V 120Ah battery can show great performance in our daily use. The BMS inside is the brain of the battery pack. The BMS is a set of electronics that monitors and manages all of the battery’s performance. Most importantly, it keeps the battery from operating outside of its safety margins. LiFePO4 batteries have a lot of advantages over their lead-acid counterparts. They’re lighter, more efficient, and charge faster.

Let’s check how to assemble a 25.6V 120Ah LiFePO4 battery after reading its introduction of it!

*Note: It is recommended that you learn some basic knowledge about LiFePO4 batteries before assembling the battery pack. Keep safe when you are assembling the battery pack.

Supplies

  • 3.2V 120Ah LiFePO4 battery cells (8 pieces)
  • There are currently three common shapes of LiFePO4 batteries: cylindrical, prismatic, and pouch. Different shapes of batteries will have a certain impact on performance. At present, the most suitable battery DIY enthusiasts are the prismatic LiFePO4 batteries, which are very suitable for both performance and operational difficulty. We recommend you purchase the Grade A battery with a high quality and reliable warranty.
  • BMS (Battery Manage System, 1 piece)
  • Connectors (About 8 pieces)
  • Others: EVA cotton, screws, ribbon cables, plastic pipes, etc.

Tool Used:

  • Spot Welder
  • Spot Welding Pen
  • Soldering Iron
  • Wire Cutter
  • Wire Stripper
  • Multimeter

Step 1: Install Signal Acquisition Wires in Sequence

First, we should check the voltage, brands, and other parameters of each battery. Make sure the parameters are consistent. Then place them neatly, and stack the battery cells properly with separators.

Connect the cells using the connectors in series while connecting the indicator cables to the CPM and the cells. Don’t tighten connectors and nuts too tightly. Rather do it firmly but gently.

When connecting the voltage collection lines (equalization lines), do not connect the external protection board to avoid accidental burning of the protection board.

Step 2: Cut the Signal Line to an Appropriate Length

Tidy up the messy lines and cut them to an appropriate length.

Step 3: Connect the Positive and Negative Wires With Connecting Pieces

Step 4: Soldering Signal Lines With Lead-Free Solder

Step 5: Put the Battery Pack Into the Shell and Fill the EVA Cotton

(EVA cotton can be shockproof, fireproof, and insulated)

The plastic shell has a good insulation performance, cells can be directly assembled into a DC high-voltage battery pack. The insulation strength is not affected by the air humidity, and the anti-lightning performance is good without grounding.

Step 6: Secure BMS With Thermally Conductive Tape

A battery management system (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack). We should install the BMS on the battery side.


First, secure BMS C- main leads to the terminal bar. Next, secure BMS to battery box mount bars.

Step 7: Connect B-Of BMS to the Negative of the Battery Pack

A BMS is one of the most important elements in a LiFePO4 battery, like the brain of the battery pack. It calculates the State of Charge (the amount of energy remaining in the battery) by tracking how much energy goes in and out of the battery pack and by monitoring cell voltages, which can prevent the battery pack from overcharging, over-discharging, and balancing all the cells voltage equally.

There are two main sets of wires we need to install, the thick wires and the thin wires. The thick wires are your charging/discharging wires and the thin wires are your balance wires. Not every BMS is the same, but most are similar. Your BMS will likely have 3 thick wires or 3 pads to solder on your own heavy gauge wires. These are the B-, P-, and C- wires (or pads for adding wires). We usually start with the B- wire. We can connect the B- of BMS to the negative pole of the battery pack.

Step 8: Connect the Positive Power Line

Step 9: Connect the Positive and Negative Power Lines to the Cap

Step 10: Check the Signal Lines in the Correct Orders

(The wrong sequence may cause BMS to burn out)

Step 11: Plug Signal Acquisition Wires’ Port Into the Interface

Step 12: Test the Voltage of the Battery Pack

We can use the multimeter to check the voltage of the 25.6V LiFePO4 battery. A multimeter is an electronic device that can measure the current, voltage, and resistance. The multimeter is also known as a voltage-ohm-milliammeter abbreviated as VOM. Two types of multimeters exist the analog multimeter which uses a moving pointer to display readings and a digital multimeter with an LED display that shows accurate readings.

Attach the multimeter probes to the positive and negative battery terminals. Then we can check the voltage on the screen. The multimeter’s red probe must be connected to the positive terminal, while the black probe must be connected to the negative one.

A fully-charged battery must indicate a slightly higher voltage than the voltage listed on the battery. For instance, a 24 volts battery will indicate about 25.6 volts when it is fully charged.

Step 13: Charging Test

If you’re doing a capacity test, be sure to charge the battery until the battery reaches 100%. Then discharge the device until the battery is fully depleted.

Step 14: Discharging Test

The discharging test of the battery is very helpful to the battery cycle life and discharge performance evaluation. We can use a professional device(Such as a Programmable DC Electronic Load) to check whether the battery works well or not during the discharging process, which can protect our battery and devices for further daily use.

When testing, there are three factors we need to pay attention to the port voltage of the battery, the resistance of the wire between the battery and the electronic load, and the temperature of the battery.