DIY a 12.8V 150Ah LiFePO4 Batteries for Trolling Motors!

LiFePO4 batteries have lots of advantages and are becoming quite in demand in the market of trolling motors. When we refer to the LiFePO4 batteries, maybe you will compare them with the GEL batteries. For a long time, GEL batteries play a role in our lives. Nowadays, we prefer LiFePO4 batteries.

As opposed to boats that use GEL batteries, electrical boats equipped with the 12.8Volt 150Ah lithium batteries are more economical, less polluting, and clearly better for the environment. The LiFePO4 battery has a longer life span and deep cycle times(even more than 5,000 times).

Are you a Lithium battery amateur and interested in li-ion battery pack assembly? Now we’d like to share the whole assembly process for beginners, which takes the 12.8V 150Ah LiFePO4 battery as an example.

*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 150Ah 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 4pieces)
• Others: EVA cotton, screws, ribbon cable, plastic pipes, etc.

Tool 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.

After testing the battery cells, we can arrange our cells as shown in the picture.

What is the epoxy board? The epoxy board is made of alkali-free E-glass cloth impregnated with epoxy resin by processing under heat and pressure. Which have extremely high mechanical strength, Insulation, heat resistance, electrical properties, and good moisture resistance properties. To protect the battery cells, we can put an epoxy board between each battery.

We place them in order and fix them with fiber tape. 

The fiber tape is made of hot melt adhesive and forms a stronger tape that is resistant to tears and has better temperature tolerance than regular tape. It is explosion-proof and leak-proof, providing high-strength insulation protection.

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.

Terminal blocks are available as rows, but each terminal connects to only a single wire, which can prevent the loosening of signal wires.

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

The thermally conductive tape for battery packs keeps the BMS in place and protects them from the shock of extreme temperature changes.

Besides, these tapes provide electrical insulation, which prevents short circuits and provides a barrier to BMS.

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.

If you connect the negative to the ground first then 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 ground as the resistance of your body is greater than the resistance of wire path and current will always flow through the lowest resistive path. Thus always connect the positive terminal first.

The wrong sequence may cause BMS to burn out

The total input and output ports of the battery pack are assembled. The assembly of this battery pack is almost done.

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.

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.

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.

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 150Ah should provide 150A for one hour. The same battery discharging at 0.5C should provide 75Ah for two hours, and at 2C it delivers 300Ah for 30 minutes.

The discharging test of the battery is beneficial 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 during the discharging process, which can protect our battery and devices in 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 storm.