Project:

Our battery pack is meticulously crafted with precision and innovation, featuring an insulator case made of fiberglass. This case is ingeniously composed of a main rigid frame and an external closure, ensuring optimal performance and durability.

The main rigid frame, constructed with sturdy beams, creates four distinct layers designed to accommodate cells and electrical components strategically. The external closure, comprised of fiberglass foils, blankets all surfaces, leaving strategically placed slots on the front and back for efficient air cooling.

Our battery pack features an impressive configuration, accommodating a total of 750 cells connected in a series of 30 parallels, with each parallel consisting of 25 cells. This configuration results in a total capacity of 8.1 kWh, reaching a maximum voltage of 126 V and achieving a theoretical peak current of 500 A.

The distribution of cells is carefully organized, with the three bottom layers featuring 9 parallels each, while the top layer houses the remaining 3 parallels. Positioned atop this layer are crucial elements, including power discharge electronics, recharge electronics, control electronics, and corresponding output connections.

Our power electronics module comprises a high-current discharge contactor, a negative pole fuse, and connectors for the inverter (positive and negative poles of the battery pack).

The Recharge System, essential for maintaining optimal performance, includes a contactor and a fuse for low-current recharge, complemented by a dedicated output cable connector.

To ensure seamless functionality and monitoring, the control electronics component is equipped with a Battery Management System (BMS) featuring sense wires to monitor cell voltage levels, a current sensor, and temperature sensors.

Completing the ensemble are the output connections, featuring a data connector, a recharge connector, and the positive and negative poles of the battery pack. Our battery pack stands as a testament to superior design and engineering, delivering unparalleled performance in the realm of electric power systems.

Innovative Welding Approach:

The project revolves around the production of a specialized busbar—a metal connecting element within the battery pack that facilitates the flow of high current between cells. This unique busbar design aims to efficiently transport the required high current, minimizing the joule effect resulting from connection resistance, all while ensuring a lightweight and flexible geometry.

The manufacturing process involves the intricate task of laser welding two sheets of dissimilar materials without the use of filler material and achieving penetration. Given the critical role played by the battery pack, the project also explores the integration of a monitoring system capable of assessing the welding process's stability and classifying common defects if detected.

In meeting the requirements outlined in the introduction, the optimal choice for the busbar conductor is a 0.6mm thick copper sheet. However, direct welding of copper to the cell case poses challenges, leading to the design of a busbar composed of dissimilar materials. The designed busbar incorporates a 0.2mm Hilumin sheet (nickel-plated steel) and a 0.6mm copper sheet.

The Hilumin sheet, being similar to the material of the cell case, facilitates easy welding. The copper sheet, chosen for its high conductivity properties, forms the second part of the busbar. The welding process involves the use of a laser with a wavelength of 1078nm. Hilumin, due to its better absorption of light radiation at this wavelength compared to copper, undergoes the welding process on its side.

This synthesis results in a carefully engineered busbar that combines the weldability of Hilumin with the high conductivity of copper, meeting the specific requirements of the battery pack and ensuring optimal performance in transporting high currents.