Our electric race car is very similar to a Formula-E car: they drive short circuits, accelerate very quickly, and power everything from a large battery pack. Our accumulator, as we call it, has around 7 kWh and contains 288 lithium cells.

These cells are pouch cells, based on a Lithium Cobalt Oxide chemistry, which means they can supply a lot of current and have a high capacity. These Lithium cells are very much like the battery inside your mobile phone.

As we all know, batteries need to be kept comfortable. Put them in a too small container, and you get situations like what happened to a certain type of big-brand phones a few years ago. The batteries in these phones were packaged too tightly and are now not allowed on airplanes anymore.

Besides space, batteries also need to stay at just the right temperature, and the right voltage. If they go outside of their comfortable range, at the very least the batteries become less healthy (so they run out sooner). In the worst case, they can even catch fire.

This is called ‘thermal runaway’, look it up.

So, it’s very important to keep all the almost 300 batteries happy and healthy, to keep our driver and car happy and healthy. I’ll explain in a bit how we keep that in check for our accumulator but, let me first go into its overall functions.

AMS Slave

AMS Slave. There are 8 of these in our accumulator

Our accumulator is smart and can activate and deactivate itself.

To do this, on both poles we have relays, so whenever it’s not connected, there is no voltage on the outboard connections.

We also have an integrated fuse, always measure the current and the voltages on the inside and have cooling integrated. Controlling all this is our AMS Master.

AMS Master

AMS Master

To check on all our cells, we measure the voltage and temperature of each cell. To easily measure each cell, we have 8 AMS Slaves distributed over the whole accumulator.

All these slaves communicate their measurements to the Master, and the Master checks if everything is OK.

Whenever the AMS sees that the batteries are becoming warm, it will increase the cooling. If it sees that some batteries are charged more than others, it balances them.

If the AMS notices something is really off, it immediately shuts down the accumulator. This means our car will stop and the cells are not taxed anymore.

Before driving again, we let the cells cool down, or charge them a little bit.

What’s interesting is that practically everything with a battery has a system like this. In our car, we also have a smaller battery, that powers the electronics and the cooling, and this battery also has its own battery management system.

Look at your Bluetooth earbuds, and they also include a (tiny) version of a battery management system.

Low Voltage Battery Management System

Formula Student Delft

Formula Student Team Delft
Stevinweg 1
2628 CN Delft
The Netherlands

Website: FSTeamDelft.nl

Facebook: fb.com/FSteamDelft

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