Introduction: 25.6V 50Ah LiFePO4 Floor Machine Battery! Lead-acid Battery Replacement

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

LiFePO4 floor cleaning machine is convenient for our daily lives. Floor machines require reliable and long-lasting backup power to ensure the job is complete without interruption. Lithium iron phosphate LiFePO4 batteries have longer life spans and higher energy densities. Compared with lead-acid batteries, LiFePO4 batteries are lightweight and maintenance-free. They are excellent partners for our housework and cleaning projects.

Do you want a durable LiFePO4 battery instead of a lead-acid one? Would you like to DIY your own battery? Here is the full tutorial in the following post.

*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

Material Used:

  • 3.2V 50Ah 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

The connecting piece has been connected to the battery cell by laser welding. Laser welding is a process used to join together metals or thermoplastics using a laser beam to form a weld.

Before we connect this group of battery cells, we should use the multimeter to check their voltage of them to ensure consistency. It is better if you have a testing device to check the internal resistance. Without testing the consistency, the battery pack may cause an accident.

Then we place them in order and fix them with fiber tape. (Made of hot melt adhesive and forms a stronger tape that is resistant to tears and has better temperature tolerance than regular tape.)

Step 2: Cut the Signal Line to an Appropriate Length

Tidy up the messy lines, then cut them into an appropriate length.

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

Step 4: Soldering Signal Lines With Lead-Free Solder

Generally, leaded solder is composed of tin and lead. The advantages of using leaded solder include: being easier to bring to working temperature, being shock resistant, and having fewer internal flaws in the structure after cooling. However, lead material is harmful to the body as it’s readily absorbed. We’d better choose lead-free solder to protect our health and environment.

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

EVA cotton can be shockproof, fireproof, and insulated, which can protect the LiFePO4 battery cells well.

Step 6: Secure BMS With Thermally Conductive Tape

Thermally conductive tapes are designed to provide preferential heat transfer between heat-generating electronic components and cooling devices such as fans, heat sinks, or heat spreaders. They are also used for the thermal management of high-powered LED’s which can run at high temperatures, thus increasing the efficiency and reliability of the system.

Step 7: Connect B- of BMS to Negative of 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 Positive Power Line

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

Step 10: Check the Signal Lines in the Correct Order

The wrong sequence may cause BMS to burn out.

Step 11: Plug Signal Acquisition Wires’ Port Into Interface

Step 12: Test Voltage of the Battery Pack

In these steps, we can use a multimeter to check the voltage of the whole battery pack. 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

The battery capacity, or the amount of energy a battery can hold, can be measured with a battery analyzer. 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. The charge and discharge rates of a battery are governed by C rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 50Ah should provide 50A for one hour.

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.