We’ve finally begun constructing parts of the car! Today we headed over to AllCell Technologies, headquartered right here in Chicago, to work on building the battery modules that will help power our car.
AllCell very kindly offered to provide us with materials and even use of their facilities to help us build the modules! Whereas our original plan was to solder the batteries together with wire (a time-consuming and somewhat risky procedure), we needed a way to cool our batteries: if lithium-ion batteries overheat, they don’t work as well and are more likely to explode. Through some research, we came across AllCell’s unique passive battery cooling technique. This technique uses a phase change material (PCM), a composite composed of wax and graphite that has a high specific heat capacity, which is crucial in keeping the batteries cool. When the temperature of the battery cell reaches the PCM’s melting point, the PCM melts, absorbing excess heat and spreading it evenly around the battery pack, and this keeps the temperature stable. (Visit AllCell’s website for a more in-depth explanation.) Pretty cool—literally!
So today (and some of next week as well) our job is to insert our many Panasonic CGR18650D battery cells into the PCM blocks to create each individual battery module. We’ll shrink-wrap the battery cells in material that will electrically isolate the cells from the PCM, which is mildly conductive, and spot-weld nickel plates to the cell terminals. Then we’ll wrap the whole block in Formex to create one unitary battery module. We’ll have about 11 of these modules in total—just under 20 kilograms’ worth of li-ion cells. Currently, after two days of work, we’re about halfway done creating all the modules!
Oh, and here’s a quote from the guys at AllCell:
“Want me to cut [the tape]?”
“Nah, have [Mark and Kevin] do it. They’re free labor.”