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Sun Mar 18, 2018 4:43 pm


. . . It turns out the Chevrolet Bolt EV battery pack is simpler to assemble than that of the Tesla Model 3, while the Tesla pack is more energy dense by weight. . . .

First, a little background on how these two packs cool their cells. Tesla’s method involves running a ribbon-shaped cooling tube between the cells. They have kept this technique since the Model S and are still using it in Model 3. Tesla has attempted to automate the assembly of the Model 3 battery pack and, unlike Model S, they are now attaching the individual cells to the cooling ribbon. This procedure is described in more detail in our article: Tesla battery pack modules made like a machine gun. It also appears likely that Tesla is attaching the cells to the cooling ribbon with glue.

Obviously, the whole process is difficult as Tesla has twice delayed the promised “5,000 Model 3’s per week” production bogey.

The Bolt EV pack is much simpler. The individual prismatic cells simply sit on a cooling plate with a thermal mat between the cells and the plate. . . .

Energy Density

At the 41:57 mark in the video we have a screenshot (below) of Professor Kelly weighing modules 1 and 10 just prior to setting them on the cooling plate. We must subtract the weight of the holding fixture to get the total weight of modules 1 and 10.

The Bolt EV has 10 modules: 8 with 30 cells each and 2 with 24 cells. Module 1 and 10 are the bigger modules with 30 cells. We also find 57 kWh of usable energy in the Bolt EV pack thanks to some sleuthing by fellow engineer Jeff Nisewanger in “ Jaguar and Chevy have LG in common.” This gives us 5.95 kWh for one big Bolt EV module, which results in a module energy density of 11.9 #/kWh.

Tesla battery module weights are based on weights published in HSR Motors online catalog (aka Jason Hughes). Usable energy per Jason Hughes is 98.4 kWh for the P100D pack. There are 16 modules in that pack, so we can get the energy density of 1 module of 10.7#/kWh. Energy density of Tesla Model 3 cells assumed equal to P100D cells. See “Tesla Model 3 2170 cells=same energy desity as P100D 18650 cells”

Therefore, Tesla’s module is more energy dense by weight than the Bolt EV module. Not a surprising finding. . . .

However, there is one caveat to all this. We have not included the weight of the case in our calculations and Tesla’s case may be heavier than the Bolt EV case. Why? Because Tesla’s battery chemistry is much more flammable than GM’s and it requires more armor to deflect foreign objects.

So, Tesla may not have as big an edge as these numbers indicate if we were to include the cases in the calculations.

Photos included.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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