WUFR20: Power Distribution Module

We are Washington University in St. Louis's IC Formula SAE team.

Overview of Team:

Wash U Racing is a multidisciplinary engineering organization that strives to design, test, manufacture, and race a formula style race car every year. We bring together engineers and non-engineers from throughout WashU to learn about the cycle of engineering and team work. We are a team of 55 members of undergraduate, dual degree, master’s, and PhD students that come together to compete in an international competition in Michigan every year in May. We seek to develop our technical, business, and interpersonal skills through the development of our racecar. This year, we put a large team focus on bridging the gap between engineering disciplines and encouraging mechanical, electrical, and computer science engineers to take on projects together to work on communicating with students with diversified skillsets.

Our Circuit Boards:

Our team will be designing two new boards for the 2020 FSAE competition, a Power Distribution Module (PDM), and an Electronic Throttle Controller (ETC). Each of these boards are heavily constricted both by rules of the sport and the car itself, but the most important ones are resistance to overheating, size, and the ability to quickly adapt the board to the changing requirements of the team. Our boards are designed in Eagle and Altium Designer.

Power Distribution Module (PDM):

On our car, we have dozens of individual components that have very specific power requirements, from the throttle position sensors that need a very stable 5 volts to give accurate values to the radiator fan that requires up to 100 watts of power to effectively cool our engine. On the safety side, we need something that can stop delivering power to a faulty circuit quickly before it damages other circuits, while doing everything it can to keep the car stable and operating correctly. With this in mind, we designed a modular power unit that can deliver 5V or 12V with included current monitoring/logging, fusing, and shutdown capabilities provided by a central controller. Everything is solid state to minimize the time required to rectify a fault. The central controller is part of the ATSAMC series of microcontrollers that have built-in CAN bus capabilities to more easily interface with our data logging system.

Overall Design:

The board design utilizes a 4 layer design to reduce the resistance between all components and the battery ground. The ATSAMC21J has 20 pins dedicated to analog inputs, and for our preliminary design we opted to use all 20 as inputs for current sensors. 1 of these is dedicated to monitoring total power draw, 1 is dedicated to monitoring the power draw from the radiator fan, 1 is dedicated to monitoring the fuel pump, and the remaining 17 are classified as "Low Power Circuits" and can flexibly monitor other parts of our data system. Each of the 19 circuits (excluding total power draw) has a current sensor in series with a P channel FET and a 3 position switch that enables us to select between 0V (disable), 5V, and 12V positive voltage. The entire board is protected by a single fuse, with two additional fuses on the fuel pump and radiator fan. Four temperature sensors strategically placed around the board allow us to better understand the thermal characteristics of our board with different cooling strategies, and a 4x7 segment display allows the PDM to quickly display status updates and error codes while in operation. The connectors on the right attach to our engine control module.