A Guide to Repairing a Lithium Iron Phosphate Motorcycle Battery
Welcome to the Cell Doctor channel. In today’s video, we will explore the process of repairing a lithium iron phosphate (LiFePO4) motorcycle battery that is currently non-functional. A friend of mine reported that this battery was short-circuited. Although it still shows some indication of life with two lines, the voltage measurement reads 9.7 volts. We need to determine if it can receive any power.
Initial Diagnosis
Firstly, we checked the voltage, confirming it reads 9.7 volts. However, the battery does not draw any current, indicating an issue. To understand the problem, we need to open the battery and inspect its internal components. Typically, these batteries contain a Battery Management System (BMS), and the fault could either lie within the BMS or the cells themselves.
Opening the Battery
Opening the battery was straightforward. Upon removing the lid, we observed the balancing leads. The board is marked SMT H04 S LED LDVD O, indicating that it includes an LED board and balancing wires. We measured the voltage on these wires to assess the condition of the cells. The cells are encapsulated in silicon, which makes access difficult. However, we attempted to charge the cells through the balancing leads to avoid complete disassembly.
Cell Voltage Inspection
The voltage readings showed 3.3 volts for one cell and 0.2 volts for another, indicating that one of the cells is dead. Specifically, cell number two is non-functional, while the other cells seem to be in good condition. We attempted to charge the dead cell by setting the bench power supply to 3.6 volts and connecting the leads. Unfortunately, the cell did not draw any power, confirming it is indeed dead.
Deeper Investigation
Given the dead cell, we needed to delve deeper. Carefully cutting the silicon around the cells, we ensured not to puncture the good cells to prevent any fire hazard. Once the silicon was sufficiently removed, we extracted the battery. With the cells exposed, we found that they are spot-welded together, complicating the repair process.
Identifying the Fault
Further inspection revealed that cell number two had disconnected from its neighboring cell, causing the battery to fail. This disconnection needed to be repaired by soldering the cells back together.
Repairing the Connection
Soldering these types of cells can be tricky, but we managed to make a good connection on half of the tab. After ensuring the connection was secure, we reassembled the battery and isolated the terminals with Kapton tape. We then reconnected the LED board to check for voltage. The state of charge indicator showed full, indicating the repair was successful.
Final Testing
We conducted a final series of tests to ensure the battery was functional. The voltage now read 13.3 volts, and the battery accepted a charge of 3 amps. Additionally, we performed a discharge test at 5 amps, which the battery handled without significant voltage drop. The ultimate test was placing the battery back in the motorcycle to confirm it starts the engine.
Conclusion
This video tutorial demonstrated the process of repairing a lithium iron phosphate battery with a broken cell connection. These batteries, utilizing pouch cells, are common in high-current applications but are more challenging to repair than cylindrical cells. Nonetheless, the repair was successful.
