The Enclosure is where our battery pack is contained and is also the most mechanically focused project currently in Battery Box.
Main Tasks for Fall 2023:
Finish Prototyping
Manufacturing Module Mounts
Finalize + Manufacturing Board Mounts
Wire Harnessing
Make Final Product 🥳
Design Requirements
The design of the enclosure is based on the following requirements:
ASC Regulations
Impounding with seals (max 4)
Safety
Battery pack cooling (prevent overheating)
Ease of removability
Size (must fit in chassis)
Weight (minimize)
Most of the requirements are pretty straight forward, we need cooling because overheating batteries can cause thermal runaway, which is when the batteries enter a sort of amplifying feedback loop where:
Battery gets too hot → becomes more resistive because it is too hot → becomes hotter because of increased resistance → gets hotter → … and this keeps repeating until the battery bursts into flames and our car is gone.
Figure 2: Thermal Runway of the battery of a car (we DO NOT want this)
We need to consider the ease of removability because we might have to take the box out to make changes to the modules or fix something inside of it. For example, if a single cell in a module becomes non-functional, we have to replace the entire module.
Size and weight are important constraints to consider because we need to make sure our box actually fits into the space the chassis provides, and it also needs to be as light as we can make it so that the weight of the box doesn’t mess with the center of mass of the car and also because more weight → more energy needed to move the car.
ASC regulations is more than just impounding and safety but those were the main ones we kept in the back of our minds while designing. Safety is just to make sure our box doesn’t separate from the car due to a crash or a roll-over (though the design of the car and ASC regulations make it impossible for a roll-over to occur anyway). Impounding is a rule that makes it so that the batteries are not accessible from outside of the box. This rule is in place to prevent teams from secretly replacing their modules with fully charged ones or from secretly charging the batteries from an external source. The event gives 4 of these seals shown in Figure 2, which is used to “lock” the box and make it impossible to access without breaking the seals (which can only be done with permission from the organizers and will be monitored, probably).
Design
The full dimension of the box is 693.25 x 400 x 235 (mm). The box itself is made up of fiberglass panels attached to an aluminum frame. On the front and back are going to be two 120mm x 120mm Noctua IPPC NF-F12 3000 PWM fans for cooling the modules.
The box sits on four steel flats and is also bolted to two more flats on the front and back to prevents lateral movement.
The modules will sit as shown in Figure 6, the CAD does not yet show the electrical components like the BMS boards that need to be attached to the modules (BMS in simple terms helps manages all the batteries' performance). The modules shown in Figure 6 below are not the complete versions either, partly because rendering the full modules with every single cell takes a toll on my computer, but the figure below is enough to get the idea across.
