VUB Racing: Buckconverter and current sensors

This year marks the fifth year of VUB Racing competing in the electric vehicle category of the formula student competition. Our team operates on a ‘Built not bought’ philosophy.

We try to build as much parts of the car ourselves. This year we built 2 new electromotors, every part (besides the magnets) is self-made, even the winding of the spools. Additionally there are many different electronical systems that have to be built.

This is where Eurocircuits comes into play. They’re a joy to work with because of their reliability and extremely quick shipping times.

This semester we added a buckconverter to our car and built some sensors.

Buckconverter

A Formula Students electric vehicle typically operates around 2 voltages. The TS voltage (the voltage the motors run on) and the LV Systems voltage (typically 12/24v and used to power everything else).

The TS voltage is capped at 600v in our competition. But to get to our LVS voltage we have 2 options. We can either use a smaller separate battery or convert a higher voltage from the TS to our LVS voltage. We went with the latter using a buckconverter. This PCB switches the TS voltage at a certain rate to step down the voltage to a desired lower point. S. Dilmaghanian decided to convert 75v from one of our 8 battery segments to 12v.

The design consists of an integrated buckconverter IC rated for our needed voltages and currents, a few input and output connectors and plenty of capacitors necessary to flatten our input and output voltage. There is also a lot of circuitry to isolate the LV ground and the TS ground. The two big capacitors are optional and will only be populated if needed. Our first larger PCB using our new favorite cad software: KiCad.

Current Sensors

Various departments of our team need to measure current. Mainly the battery team and the drivetrain team. Battery engineers want to know how much power is being provided and the drivetrain engineers want to know how much power is being used at the different stages of the powertrain. Because of this one simple solution is desired. One PCB that provides a useful readout for any PCB. This general solution was made possible by the MLX91215. Using it, we made this simple breakout board.

We integrated these in our proprietary sensor nodes who communicate the relevant data to the rest of our car using CAN. A reliable solution made possible by Eurocircuits. This was proven at our latest competition: Formula Student Netherlands.