University of Extrication: Thermal Events: Part 1

This University of Extrication multi-part series comes right from the headlines of today’s newspapers. The topic being addressed is what vehicle engineers call “thermal events” involving liquid-cooled, high-voltage, lithium-ion batteries...


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As we explain the layout of the battery, refer to the image to see exactly what we are talking about. The VOLT’s 400-pound battery is T-shaped and fits beneath the floorpan along the center tunnel and below the rear seats. When discussing the battery, this author frequently refers to its design as a “loaf of bread.” The cells of the battery are like slices of bread, and when set together with their connecting wires, they form the “loaf of bread.” The cells that are visible in this rendering are held in place with plastic frames called “repeater frames.” The VOLT battery consists of several of these connected modules, all within one big battery enclosure.

It has been mentioned that the VOLT battery is liquid cooled. What is critical for responders to understand from this rendering is that between each of the narrow lithium-ion cells are even thinner plates called “thermal fins.” These paper-thin, tin foil-looking fins are what cools the VOLT battery’s lithium-ion cells. To accomplish this, each fin has liquid lines running through it. The antifreeze solution enters the VOLT battery at the front end and circulates through the repeater frames, tubing, hose connections and all of these thermal fins. Entering as cool solution and exiting as warmed coolant, the system maintains optimum temperature for the lithium-ion cells to function as designed. The radiator is under the hood at the front of the vehicle.

 

Location and design

The second point that must be gained from this cutaway image is the location of the battery’s electrical components. In the VOLT design, all wiring, connectors and terminals run along the very top of the repeater frames. Like the liquid coolant, the high-voltage current flows in through one orange connector at the front of the battery and runs through all 288 cells. The 360-volt DC current flows out of the battery through a different orange connector at the front of the battery.

Now that you have a better understanding of the design of the VOLT battery, we will look at the 2011 fire incidents where a Chevrolet VOLT was present and explain what investigators determined happened in each case.

TASK: Upon the conclusion of this series, fire service responders shall be able to develop department guidelines for dealing with liquid-cooled, high-voltage batteries at a vehicle collision or fire-related incident. n