Hey all! Mathijs here again, last time I told you some things about the accumulator: the lithium cells in there and the AMS slave, a PCB that will measure the voltages and temperatures of these lithium cells. In this blog I will update you on the battery cell selection and the AMS slave!
As mentioned in the previous blog, our car is powered by a lot of lithium polymer battery cells. There are a lot of different variants of lithium cells, and I wanted to find the best suitable one fur our usage. This meant having to find the right balance between weight, volume and capacity. What I tried to optimize for this year, was the internal resistance of the cells. The internal resistance of the cell determines how much the cell heats up when used, and thus how efficient it can provide energy. If we are able to use a cell with a low internal resistance, less energy gets wasted on heat, so that we can use a smaller capacity cell. A smaller capacity often results in a cell that is lighter, smaller or both. It also makes the accumulator easier to cool! After some extensive testing, we found the ideal cell for us. Unfortunately, the manufacturer told us that our chosen cell was not suitable for us, since the fault rate is on the high side and we want to have a very reliable accumulator. For this reason we had to change to another cell pretty last minute. Luckily that one was also high on our wish list!
Last blog I mentioned getting started on designing a PCB; the AMS slave. At that time, I just finished the schematics for it. After that, the fun (also the hardest) part started: routing the PCB! This is when the schematics get translated into actual components that have to be connected by copper traces on the PCB. Where to place all of the components, and in which way they are connected, is completely up to you. I just finished the first version of the AMS slave, it’s send out for production now! This version will be extensively tested when it arrives, so that all the problems it may have can be taken care of when designing the second version. The second version of the AMS slave will eventually be used in the car!
What’s to come?
What’s next for me, is building the test plan for the AMS slave. The tests should include all the things that the PCB must be able to do when it’s used in the car. This requires some forward thinking, since the car doesn’t even exist yet! Luckily I have some references from testing that has been done in previous years. Next to that, production is starting in the new year! We have acquired all this knowledge and designed all these parts over the last few months, and now it will actually become reality. For me, the most important part of the production is the accumulator. I will probably be involved in the construction: building the modules in which the cells are housed, wiring all the components in the accumulator, laser welding the cell tabs together and more. Really looking forward to learn some new skills!