Share: DIY A 12V 120Ah LiFePO4 Battery For My Travel Trailer

QHLifePO4Battery

New member
Hello, folks.

Several months ago, my AGM travel trailer battery is broken. After comparing YouTube and Google, I decided to build a 12V 120Ah LiFePO4 battery. I buy the battery cells and the kits online. After preparing all the tools and materials, I start to build it and finally got it done. I'd like to share the full process.


Materials Used:
  • 3.2V 120Ah LiFePO4 battery cells (4 pieces)
  • BMS (Battery Manage System, 1 piece)
  • Connectors (About 4 pieces)
  • Others: EVA cotton, screws, ribbon cables, plastic pipes, etc.

Tool Used:
  • Spot Welder
  • Spot Welding Pen
  • Soldering Iron
  • Wire Cutter
  • Wire Stripper
  • Multimeter
Assembly Process
1. First, place four battery cells on the work table. Before we assemble the battery pack, we should check the quality and ensure consistency, which means they are produced by the same brand with the same voltage, and capacity.

12120-1.png

2. Next, we can put the epoxy boards between the batteries. 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.
12120-2.png

3. 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.
12120-3.png


4. 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.

12120-4.png

5. Terminal blocks are available as rows, but each terminal connects to only a single wire, which can prevent loosening of signal wires.
12120-5.png

6. After soldering the wires (the balancing leads and the charging-discharging cables), we can tidy up the messy wires.
12120-6.png

7. 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.
12120-7.png

8. 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.
12120-8.png


9. 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.
12120-9.png

10. If you connect the negative to the ground 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 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.
12120-10.png


10. Install Positive Power Wires To The Battery Pack

11. Fix The Temperature Measuring Probe Near The Battery Pack

12. Install Positive And Negative Power Lines To The Cap

13. Fill EVA Cotton

14. Check The Signal Lines In The Correct Order

15. Plug Signal Acquisition Wires’ Port Into Interface

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.

Finally, after several tests, my battery pack has been done and works well with my travel trailer.
 

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