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Design Report of the High Voltage Battery PackforFormula SAE ElectricLiam West, Barry Shepherd, Nathaniel Karabon, Josh Howell, Mike PyrtkoDepartment of Mechanical EngineeringUniversity of Wisconsin-MadisonDecember 12th, 20161

Executive SummaryThis year, Wisconsin Racing (Formula SAE at UW-Madison) is building its first ever fullyelectric race car in addition to the combustion engine powered race car that it traditionally builds.Powering the electric race car is the accumulator, which is a custom-built lithium ion battery packthat includes all of the controllers and hardware necessary to regulate the battery, as well as the powerdistribution for the motor controllers. Being that this is the first electric vehicle that Wisconsin Racinghas attempted to make, a significant amount of time was devoted to background research and decisionmatrices to ensure that the accumulator met the performance goals and followed all of the FSAErules. Using a lap simulator for the endurance event at the FSAE competition at Lincoln, the electricalperformance goals were established. Extensive lists of components such as battery cells and batterymanagement systems were created so that potential options could be compared side-by-side to findthe optimal component. To meet the FSAE rules, structural and thermal FEA was performed on thedesign as it progressed. Constantly changing designs in the rest of the vehicle meant that theaccumulator design had to be continuously updated to accommodate those changes.After months of iterative development, the structural design of the accumulator has beenfinalized and is being fabricated. A cooling system has been incorporated into the accumulator thatcan be modified once the thermal model has been validated against test data to ensure that the cellsremain within safe operating temperature ranges throughout the endurance event. In addition, aprototype for the braking system needed for the accumulator charging cart to meet FSAE rules hasbeen fabricated.The next steps for the project are to fabricate the accumulator structure and purchase all ofthe components. Once the accumulator has been put together, testing both inside and out of thevehicle will be conducted to ensure proper operation of the system.2

Table of ContentsExecutive Summary . 2Introduction - Background . 5Reaching Current State of Design . 5Background Research . 6Battery Cells . 6Rules and Regulation . 6Current Design . 7Cells . 7Cell Selection . 7Cell Configuration . 9Cell Temperature Monitoring . 12Battery Management System Selection . 13Charging System . 14Charging Cart . 14Charger. 14Cooling System . 16Separation and Connectivity . 16Fusing . 16Accumulator Insulation Relays . 17Wiring . 18Overall Accumulator . 20Electrical Parameters . 20Physical Parameters . 21Location in Vehicle . 22Analysis . 23Finite Element Analysis . 23Cooling . 27Calculations . 27Thermal Modeling . 29Appendix A: . 32Relevant FSAE Rules . 32Table A-1 Relevant FSAE Structural Accumulator Rules and Regulations . 32Table A-2 Relevant FSAE Charging Rules and Regulations . 33Table A-3 Relevant FSAE Accumulator Electrical Rules and Regulations . 34Appendix B: . 36Decision Matrices and Informative Calculations . 36Table B-1: Battery cells that were considered for using in the accumulator. . 363

Table B-2: Battery management system decision matrix. . 37Figure B-1: Equations used for calculating the specific heat of lithium ion batteries using a data from a calorimetertest. . 38Figure B-2: Equations used for calculating the brake force required to stop the charging in 0.5 [m] with springdeflection of 0.01 [m]. . 38Appendix C: . 39Component Datasheets. 39Samsung INR18650-25R Technical Data . 39Energus Power Solutions Li8P25RT Technical Data . 39Orion Battery Management System Technical Data . 40Coroplast High Voltage Wiring Technical Data . 41TE Raychem 22 AWG Accumulator Low Voltage Wiring Technical Data . 41TE EV200AAANA Accumulator Insulation Relay Technical Data . 42Eaton Bussman 170M3418 Main Tractive System Fuse Technical Data . 42Eaton Bussmann 160LET Motor Controller Fuse Technical Data . 43ElCon PFC 5000 5kW 96V 44A Battery Charger Technical Data . 43References . 454

Introduction - BackgroundEvery year, the Society of Automotive Engineers (SAE) holds a competition for collegeundergraduates to design an automotive vehicle. The goal for the competing teams is to design andbuild a 1/3-scale Formula-style race car with the best overall design, manufacturing, performance,and cost. Going through the design process from concept to completion gives students pricelessexperience in design, simulation, and hands on knowledge. Although Wisconsin Racing, theUniversity of Wisconsin - Madison’s Formula SAE (FSAE) team, has been successful for the lasttwo decades in the internal combustion engine competition, the rise in global warming and increasingpollution levels, has made it essential to find a viable alternative to the internal combustion enginepowered car [2]. With this responsibility, it is imperative that engineers have the necessaryknowledge and experience with fossil fuel saving methods. This year, the team has put it uponthemselves to build two cars, the traditional combustion vehicle and an all-new formula electric racecar. This will greatly expand the field of expertise on the team and prepare us for an evolving jobenvironment. However, designing an electric vehicle for the first time will be a tremendousundertaking. In order to make this project more manageable, both vehicles will attempt to use asmany of the same components as possible. To further insure our success, we have taken one of themost dissimilar vehicle design component under the guidance of a knowledgeable faculty advisorthrough senior design.The aim of this project is to design and build the high voltage battery pack for a FSAE electricracecar. The high voltage battery pack will need to contain the battery cells, fuses, batterymanagement system and much more. The driving constraints for the project are the FSAE rules,performance goals, and integration within the rest of the vehicle as it is being designed. Because theteam has never built a high voltage battery pack before, extensive background research andcalculations were performed to begin the design. One of excellent source of inspiration was theaccumulator designs of other FSAE electric teams [1][3]. As the design progressed, numerouschanges had to be made to comply with all FSAE rules and to be compatible with constantly changingpackaging constraints from the rest of the vehicle. After months of hard work, the design for theaccumulator meets all goals and requirements has been finalized. The next steps are to order all ofthe necessary components and begin fabricating the accumulator with the goal of being able to testin the spring.Reaching Current State of DesignReaching the final accumulator design was a complex and iterative process. With no clearstarting point and multiple ways to design an accumulator, significant time had to be devoted tobackground research, calculations, and ideation to ensure an optimal final product.5

Background ResearchBattery CellsBattery Manufacturers. It was quickly d