A Little Secret GM Isn’t Telling Us About Improving The Bolt EV Battery
What’s one of the biggest complaints about the Chevrolet Bolt EV (besides the seats)?
Remember the song “I can’t Drive 55”? It’s about the same thing when it comes to charging speed. Why won’t GM make the Bolt EV charge faster?
Our resident heat transfer expert Keith Ritter made a very interesting discovery when analyzing the Bolt EV battery pack. It was part of a detailed heat transfer investigation of both the Tesla and the Chevrolet Bolt EV batteries.
Keith modeled the heat transfer aspects of the Bolt EV and we discovered that the pinch point for heat transfer out of the cells is the metal “fins” that go between the cell pouches and transfer heat down to the bottom plate. Those metal fins essentially limit the pack charging rate to what it is now.
Here’s another interesting discovery we’ve uncovered in the analysis: If you add another cooling plate ON TOP of the cells you get a factor of 3.5 heat transfer improvement. A factor of 3.5 I asked? It’s got to be a factor of 2. Two plates=twice the heat transfer. Right?
Wrong. There’s a compounding effect. Not only have you added another plate you have cut the effective length of the fin in half, thus the compounding effect.
Now get this. The top of the cells is nice and smooth exactly like the bottom of the cells.
Here are the photos that show that:
Image 1: Bottom of the Bolt’s cells. Photo courtesy John Kelley, Weber University
Image 2: Top of Bolt’s cells. Photo courtesy John Kelley, Weber University
So the top of the cells are just ready to slap on another plate and we now have enough heat transfer to up the charging rate to 100+kw!
Sounds good to me!
*This article was written as a collaboration with Keith Ritter (HVACman)