BMS case study: bullet design race car goes on solar power

A bullet cutting through the air became an inspiration to this futuristic looking race car. Very talented engineers from Sweden, Chalmers Solar team, built it and used ENEPAQ battery management system (BMS) in it. This car competed in an international event for solar powered cars – Bridgestone World Solar Challenge 2023. This kind of event drives advances in renewable energy and automotive technology.

What “mere” students can do and achieve

Bridgestone World Solar Challenge is a 7-day race where the cars compete to complete the course, crossing the Australian Outback, traveling from Darwin to Adelaide. Teams all over the world travel a total of over 3000 km during the competition, and the cars are solely powered by solar cells.

“We have three main goals. Partially to win the challenge of course. Partially to enable the engineering students partaking to expand their knowledge. And partially to push technology forward through showcasing what “mere” students can do and achieve. The long-term goal is to push for innovative solutions toward a more sustainable future”, – explains Chalmers Solar Team 2025 manager Rickard Lennernäs when ENEPAQ asked what fueled the team to participate in such kind of international event.

Chalmers Solar Team participated in Bridgestone World Solar Challenge in 2023. It took 1,5 years to finish their race car, called Allswinn.

“The decision to go for a TinyBMS came down to a lot of things. Among them the fact that ENEPAQ is close to us geographically (ENEPAQ is headquartered in Lithuania, CST team is from Sweden) which means lead times are short. The specifications also matched what we were looking for well.”

“The project was started before the Bridgestone World Solar Challenge 2019. It was a teacher and some driven engineers who in a very short amount of time created a solar car for the challenger class from scratch. This was Alfrödull and it was the start of the team. The design was fairly unusual compared to established solar cars but laid the groundwork for what was to come. With the second and third cars came Sköll and Allsvinn. These cars follow a bullet design, drawing inspiration from the aerodynamic shape of a bullet cutting through air”, – explains R. Lennernäs.

All competences tested at the same time

Although the competition itself sounds like a huge adventure, not all parts of the process are smooth and pleasant.

As competition takes place in Australia, the distance from Sweden makes it even more complicated.

“The time spent in Australia is its own kind of challenge. Suddenly everything is much higher stakes. If something happens, the time you must fix it is much shorter. This means that all your competences are tested at the same time, including how much sleep you need to function. The highs are constant however, intermixed with the challenging times”, – recalls Chalmers Solar Team manager.

According to him, there is a fun and rewarding part of team work too.

“Spending time together as a team, seeing how we are ticking off their goals, solving problems, to finally get to the stage where we have a car that’s functioning and moving has been incredibly fun and rewarding. Every check point that we got to in Australia was also a highlight in its own way”, – explains R. Lennernäs.

Lot of weekends dedicated to work

Chalmers Solar Team (CST) consists of 25 students and is aimed at growing. As team manager told ENEPAQ, gender distribution is a bit skewed, so while they do have women taking up some of the key roles in the team – would like even more.

“Since we’re a university project we’re mainly using campus facilities for our work. The university happens to be quite well equipped, so that works out well for us. CST is a team that is not course based; therefore, we all do this in our free time. So, working evenings are a given, and nights are often required. There have also been a lot of weekends dedicated to work”, – says R.Lennernäs.

As you might expect, teamwork is well organized, but some chaos is always in the place too.

“Completing a project of this size wouldn’t be possible otherwise. However, at our core, a lot of us like the creative chaos, and we will let that shine through when possible”, – smiles CST team manager.

The TinyBMS proved to be a good option

Solar car built by CST used battery management system (BMS) that happened to be ENEPAQ TinyBMS. R. Lennernäs named three reasons for this decision.

“The decision to go for a TinyBMS came down to a lot of things. Among them the fact that ENEPAQ is close to us geographically (ENEPAQ is headquartered in Lithuania, CST is from Sweden) which means lead times are short. The BMS specifications also matched what we were looking for well. The project also has a limited budget. Therefore, student team pricing is always something one needs to consider. TinyBMS proved to be a good option there as well”.

According to team manager, the battery management system (BMS) they received from Enepaq (TinyBMS) worked great during the Bridgestone World Solar Challenge 2023.

“The performance of the BMS was crucial to getting as far as we did in the Bridgestone World Solar Challenge. Unfortunately, because of rule changes and a change in design philosophy of the car, we are unable to go with TinyBMS for our 2025 challenger. We have seen that you at Enepaq seem to be working on a new BMS that could potentially handle 30+ batteries in series – which would then again make it an option!”

Things to be nailed at 2025 competition

Although Bridgestone World Solar Challenge 2023 was a good opportunity for the Chalmers Solar Team to shine up, it wasn’t the best race they had. Allsvinn couldn’t make all the way to Adelaide. In the end it drove 2764.4 Km out of 3022.

As R. Lennernäs explained, the main issue came down to routine and organization.

“The issues we experienced were of the nature that they would have been caught had we had more testing done before the race. So that is one of the things we’re really hoping to nail next time around. The car was good enough to reach the goal, so the issues were unfortunate. We truly believe that this will be the year for CST”.

Team’s goals for Bridgestone World Solar Challenge 2025 are twofold: finish the race and also become the best team in Sweden.

“We feel both are realistic goals and we’re optimistic about being able to match them. We’ve already reached one of the goals in part. During the iLumen European Challenge 2024 we took home the National Champions title with Allsvinn. So, the goal now is that the new car will be even better”, – says Chalmers Solar team 2025 manager.

Key to success – dream big while still being realistic

R. Lennernäs thinks that the engineering students available at Chalmers are of a very high standard, but the team is still very young and needs more structure.

“Team had no time to implement proper structures, which in the end makes for a lot of small bottlenecks. A key element for success will therefore be implementing the structures needed to make our workflow even better”, – he explains.

He also says that another component is getting sponsors to finance the project. Well-functioning partnerships are essential.

“Other than that, testing, being data driven in our development, and daring to dream big while still being realistic are all things that will be setting us up for success,” – reveals R. Lennernäs.

For the end, he adds that the team’s next car most likely will become larger, adapting to new rules regarding allowed solar cell area.

“We will be keeping changes under wraps but hope you guys are excited to see what’s to come”.

More information about the Chalmers Solar team can be found there: https://www.chalmerssolarteam.com/

More information about ENEPAQ TinyBMS you can read there: https://enepaq.com/product/battery-management-system-bms-150a-set-tinybms-s516/