12.8V 50Ah LiFePO4 Battery Assembly! DIY a Backup Solar Power

If you need a small voltage and capacity of LiFePO4 battery pack, the 12V 50Ah one is worth a try. With no acid in the lithium-ion battery, you’re able to safely mount it in any position. This makes Li-ion batteries perfect for marine, RV, campers, golf carts, travel trailers, and off-road and off-grid applications!

In the following post, we’d love to share you with the full battery pack assembly tutorial of a 12V 50Ah LiFePO4 battery. Do you want to build your own battery? Follow us and finish it step by step.

*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.

Materials Used:

• 3.2V 50Ah LiFePO4 battery cells (4 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 4 pieces)
• Others: EVA cotton, screws, ribbon cables, plastic pipes, etc.

Tools Used:

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

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.)

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.

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

If you connect the negative power wire first then the current will flow through the positive terminal to your body when you connect the positive terminal. But when you connect the positive terminal first then while connecting the negative terminal the current will pass through the negative to ground wire instead of your body to the ground as the resistance of your body is greater than the resistance of the wire path and the current will always flow through the lowest resistive way. Thus always connect the positive terminal first.

We can not put the battery pack into bare condition. It is an excellent choice to put it into a plastic shell. Compared with the aluminum shell, the plastic shell has a good insulation performance and is cheaper.

Most of the cases of lithium batteries are mass molded manufacturing, production of high cost, and personal customization of the case is difficult. You can look for the case on sale online and pay attention to the size.

After putting the battery pack into the shells, we can fill the EVA cotton. 

EVA cotton can be shockproof, fireproof, and insulated, protecting the battery pack well. It can reduce the expansion force of the battery and improve the service life of the battery

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.

After soldering the wires (the balancing leads and the charging-discharging cables), we can tidy up the messy wires.

The wrong sequence may cause BMS to burn out！

The signal acquisition technology can provide accurate parameters for battery balancing, SOC estimation, and BMS centralized monitoring to meet the actual requirements of battery packs.

Using the signal acquisition technology, the voltage signal, temperature signal, current signal, etc. In addition, data from the battery pack CAN be transmitted to the central control unit.

This is the final step of the entire assembly process. Finally, the total input and output ports of the battery pack are assembled. We can prepare for the next battery performance tests.

In this step, 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 12 volts battery will indicate about 12.8 volts when it is fully charged.

Through the test, we can check that the charging value is normal and that the battery is abnormal during the charging process. We need to pay attention to the battery charging time and charging current.

The discharge 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.