FSAE Accumulator Box

Summmer '20 - spring '21

technical skills: Battery Theory, Mechanical, Simulation

The aim for this project is to design and build a battery pack for a FSAE electric race car. This battery pack will need to contain 18650 battery cells, fuses, and several electronics for battery management systems. The driving constraints for this project are the rules from FSAE. Since this is the first time the team has built a high voltage battery pack, extensive background research and calculations are performed to begin the design. Our goal for this design is to interface with the Curtis 1239E-85 Inverter which has voltage range of 60-170V and 500-650Arms.

Li-ion cells are the major components that create the battery box that it determines the performance and power delivery of the racing car. A lot of time to spend on researching different cell selections. As different Li-ion cells have different characteristics, based on our configuration (also limit from the rules) of driving the power train, we narrowed the cells by five options and 2 configurations using 18650 cells.

However, given that the datasheet of the cells from the manufacturers are often unreliable, we want to make sure the cells we want meet our requirements. Thus, we set up a testing station at our member’s garage. For the testing, we want to test the main features: capacity and currents. Thus, we set up different discharge current to measure the cell’ capability. After conducting the test, we choose P26A from Molicell as it is a quality choice with consistent discharge performance from low to high current.

After finish selecting the cells, based on our configuration, we need to design the module, and connect them together. Our battery pack is a 40s12p configuration which result in up to 168V and 400A max voltage and current, with 40 modules of 1s12p. For thermal simulation, I did the verification model for Passive Cooling. Since when discharging current, the cells also dissipate quite an amount of heat, and it decrease the efficacity of the power delivered. Thus, a verification model is necessary. Using Simscale for thermal simulation, we assumed to have the module discharging at 15A in a free air environment and we can see the hotspot that might need further attention.

An accumulator container is required to house the batteries and any other necessary components. This container must be easily removable from the vehicle to transport to the charging station at the competition. The main structure of the accumulator also contains different PCBs and Connectors, not only Battery. Thus, we need to understand the electrical system of the whole High voltage system to planning wire harnessing and connectors. The whole electrical system is to make sure all signals are monitored and detect failure.