Throughout the course of our senior project, we ran into many obstacles that caused some delays in certain areas of the overall project completion. Perhaps one of the most difficult task for our project was being able to get full amount of funding required for our project. The total projected funding needed was over eight thousand dollars. Thankfully we had many sponsorship's that were able to provide either free software, circuit board printing, and discounted/free components, which helped reduce the total cost of funding required. However, we still had issues for most of the funding, so we just made due with what the IRA funding that was provided for and used that to purchase most of our components.
Another challenge that presented itself was the use of the Altium Designer software. Although Altium is a great PCB software, it still provided us with some difficulties that took a rather long time to overcome. For example, the components that were being used for our project were automotive rating standard, so the installed Altium libraries did not have most of our components. We had to research and find multiple libraries that included our components and then install the library into Altium. However, a select few of our components did not have libraries that could be found on the internet, so our team had to read the data sheets provided by the manufacture and create the component using Altium's "Custom Component" feature.
The most difficult challenge with the project was the PCB layout and routing. Before the routing can begin, we had to fix the several error's that popped up as a safety check to ensure that all components are wired correctly and there are no floating pins. Once we received a list of zero errors, the component placement and routing began. By following the Texas Instruments data sheet for component placement, we were able to design the most efficient layout possible. Instead of using the function "Auto route" in the software Altium, which will automatically route the layout within two minutes, we decided to manually route the layout ourselves. Although it took over 30 hours to route the board, it gave us the freedom to make certain traces between components thicker, to allow more power flow in the trace if needed. This was the difficult method to route the board because we had to spend many hours making sure that we had the right trace thickness for every component, however it was the method that would receive less error's in the DFM Gerber files (Design for Manufacturability). Performing a DFM check will identify and notify customers of underlying design issues in the PCB, which can cause errors during manufacturing. By auto routing the board, there is a higher chance of there being many errors the Gerber files and will lead to more time being spent on debugging the issues.
Due to time constraints, we were unable to complete the battery pack accumulator. We have an initial design for the pack accumulator and hope to finalize it during the time period of summer 2017. The finalized design of the battery pack will contain at least 40 cells in series and four in parallel; therefore, we need at least three PCB’s communicating with each other. We will also be asking more company's for funding or sponsorship's so we can buy the appropriate batteries required for the race competition. Our team will plan to incorporate an Electric Control Unit (ECU) system before the Formula SAE Competition in 2018. Implementing an ECU on the BMS PCB will allow communication between the batteries and the other subsystems on our vehicle.
In conclusion, our battery management system (BMS) was successfully designed and manufactured on a multilayered PCB. Utilizing industry standard test equipment, the BMS was able to meet Society of Automotive Engineering regulations. Incorporating thermal planes, the BMS was able to operate in safe thermal conditions while under an extensive load. The implementation of passive cell balancing on the 16 battery cells was done successfully using the TI software that showed the voltage level and temperature of every pair of cells. We also gained invaluable experience with surface mount soldering, learning new software, building custom components. Although we did hit a few speed bumps along the road, such as searching for the component libraries, creating custom components, numerous schematic error's, and the tedious and time consuming board layout/routing. Lastly our team learned about the characteristics of passive cell balancing and its importance for improved battery life expectancy. At the end of our semester, we were able to successfully showcase our results.