Not Too Hot, Not Too Cold—How to Please an EV Battery

Coda EV

In the coming electric car wars, Coda Automotive, which we've written about before, is one of the scrappiest contenders. The startup car company wants to take on established giants like Chevy and Nissan, and it’s planning to deliver its first cars to customers by the end of this year (for something like 37 grand, after the federal rebate). Folks who choose to buy electric will probably let appearance be a major deciding factor, and Coda actually takes pride in its plainness. But looking at the inward anatomy of the car is just as important, and Coda has recently filed patents enabling it to give a closer look under the hood.

Or under the chassis, rather. The core of the Coda is the battery—700 pounds of cells, five feet long by four feet wide, running beneath the cabin. Batteries, like people, can be finicky about the weather. If they get too hot, they age prematurely; if they get too cool, you don’t get the range you need. Different EV companies have tackled this problem in different ways. Nissan, for its upcoming Leaf, has opted for a passive thermal management, using just an internal fan to evenly distribute heat (Wired.com’s Darryl Siry called this "cut[ting] corners on the most critical aspect of electric vehicle technology"). Coda, for its part, is using an active thermal management system: the same HVAC system that cools and heats the car’s cabin also cools and heats the battery.

Here’s how it works. Say the battery is becoming too hot. The car’s HVAC system produces cool air, sending it down to the battery. But here the engineers encountered a sort of spatial puzzle. "Air heats up as it moves along the cooling path," Coda engineer Broc TenHouten tells Fast Company. The simplest thing might be to simply send the cool air along the five-foot length of the battery. Rather than do that, Coda’s engineers struck on an idea. Their design pulls the air into the center of the battery, and then has it radiate out through little rivulets across the battery's width. "By shortening the distance the air needs to travel, you reduce thermal gradient in the pack," says TenHouten.

It’s a neat piece of engineering geekery. But it’s hard to imagine that it will make the difference when consumers come to make their choice. With its competitors offering a lower price ($33,500 for the Chevy Volt, and around $25,000 for the Nissan Leaf, after a rebate), Coda may have to make its case that it’s design is superior more loudly and persuasively if it wants to wind up the victorious one in the David vs. Goliath narrative it's concocted for itself.

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