Caution, high voltage!

Hi everyone! I’m Mathijs, a third year bachelor student in Electrical Engineering, and I’m currently following my minor at Formula Student Team Delft. I’m in the electrics department, and together with the total team of 10 other minor students, 50 part-timers and 16 full-timers, I will be building the DUT19!

The Accumulator

I’m working on most of the electronics inside of the accumulator. This 600 Volt, 150kW monster of a battery stores the energy and provides the power that the car needs to drive. The accumulator container consists of the lithium battery cells, the AMS master (Accumulator Management System), the AMS slaves and other components like relays, fuses and a current sensor.

Lithium Cells

There are a lot of different battery chemistries out there. We want to use one which is rechargeable (dûh), lightweight, can provide a lot of power and can store a lot of energy. You quickly find out that Lithium cells are most suitable for this. When selecting our perfect Lithium cell, we look at its capacity, weight, size, maximum current output, internal resistance and so on. I have selected the best (in theory) 3 cells, and we ordered a few samples of each to test them out. We test them by continuously charging and discharging the individual cells at really high amperages, to simulate what happens when it’s used in a race. We measure the voltage, current and temperature of the cell. With this data we can calculate things like: the actual capacity, the internal resistance and the cells voltage/state of charge curve. By looking at the data acquired during these tests, we will decide on what cell we will actually use!

AMS slave

The AMS slaves are PCB’s placed on top of the lithium cells that contain connections for temperature and voltage sensors. All the data measured by the AMS slaves is send to the AMS master PCB, which communicates with the rest of the car’s electronics. The AMS master is done by another electrical engineer, but I will be designing the slaves! By rules, all the individual cell voltages have to be measured, together with the temperature of 30% of the cells. That’s quite a lot of data, since there are 288 cells in the accumulator. These cells are placed in different modules, and each module has its own AMS slave PCB on top. Since the modules contain a different number of cells than last year, the AMS slave needs to be redesigned. This is done in Altium, a schematics and PCB design program. Really fun to actually do some PCB design!

If you would like to know more about what we do at DUT Racing, send me a message, check out our socials (@fsteamdelft) or walk by the Dreamhall some time!