Cooling Chat With Formula
- Shem Kim
On Jan. 15, 2024 we talked with Rohan (UWFE’s battery guy) to get his opinion on our pack’s cooling. Key concern/question was whether our cells were too close packed to provide space for air to pass through. This page is a general, bullet point info-dump of we got from the conversation since they have a lot of experience:
Formula’s pack consists of around 800 cells and has a current draw ranging from 80A to 130A. In comparison, MSXV’s pack consists of 288 cells and draws roughly 10A. The main factor that makes our pack hotter is that our car is 100% going to be in a very hot environment whereas Formula’s ambient temperature depends on the season that their competition is in (it can be in the Winter or the Summer).
From looking at the module spacing within the pack and the cell spacing within the modules, Rohan didn’t think the spacing between cells is very concerning. He did have a separate spacing concern regarding the empty space existing within the entire box itself (indicated in red in Fig. 1.0). He said that when the modules move within the enclosure (from turning corners, sudden acceleration/deceleration, etc.), it is ideal for everything within the box to move as one (think a full water tank vs. half filled water tank). Unlike the modules placed along the width of the box (which is hugging the walls), the modules along the length of the box leaves empty room, which can cause the floor panel to break. This is the case even if we bolt the modules down to the floor.
The main cooling concern he believed we may have is with the lack of fresh air reaching the modules in the back of the pack. Ideally, what he suggested we might do is create more inlets on the side panels of the enclosure (Figure 2.0) to allow another source of fresh air for the modules closer to the back of the pack. Whether this is something we critically need is something we would have to actually test to know for sure.
Figure 2.0: Adding a side opening can allow fresher air to reach the back of the pack
Formula does their battery simulations using StarCCM. From this conversation about cooling and a previous conversation we had with him about waterproofing, it is something they used fairly extensively to validate their design. StarCCM is owned by Siemens, and we do not have access to it.
Main Impression and Takeaway:
Just based on intuition, Rohan doesn’t find the cell packing within the module a concern for cooling. There are some design changes that can optimize cooling, but we do not know whether such a design change is necessary without testing. Battery should do a full pack cooling/thermal testing so that we have an idea of how effective cooling will be for our pack. This test will be planned and done in junction with all the other things we already have in our timeline, stopping everything we’re doing to focus on this testing is wholly not necessary and will only push us back farther. If something really is terribly wrong (which we think is most likely not going to be the case) then that will have to call for a core/leads meeting immediately. But if worst comes to absolute worst, we can ultimately just drive slower.