EVs Fire Up Pyroswitches to Cut Risk of Shock After a Crash
1Reported today in Wired.
After more than a century of powering their wares with engines that produce hundreds of small, carefully controlled explosions each minute, the auto industry is moving toward a battery-driven future. But that doesn’t mean one without any helpful explosions. Last month, industry supplier Bosch revealed details on what it calls the pyrofuse, a new safety tool for electric cars.
When the system detects a crash, its uses a bit of combustion to fire small wedges into the high-voltage cables, severing the connections between the battery and the power electronics. The idea is to reduce the risk of electrocution for first responders.
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Here’s why that’s necessary: Conventional cars run about 12 volts of power, but many electrics use 400 volts. The new Porsche Taycan uses double that. That power bump has pushed the auto industry to develop new ways to keep everybody safe. Along with careful insulation of battery packs and high-voltage components, automakers and suppliers have developed a variety of pyrotechnic safety switches that activate in the event of a crash. Autoliv’s Pyroswitch throws a switch to disconnect the power source from the circuit board. Tesla has patented an “arc-suppressing gas blast in pyrotechnic disconnect” that appears to work similarly.
Bosch’s system goes further by actually cutting wires. “It’s a secure disconnection,” says Thorsten Koepke, the company’s product manager for semiconductors, “a physical opening of the wire.” His team produced the chip that uses deceleration and other data from the car to identify a crash. They originally developed the chip for use in airbags, but it serves the same function here. The exact workings of the system, including the conditions under which it will trigger, are up to the automaker, but the general idea is that the chip triggers a small explosion, similar to the chemical reaction that inflates an airbag. But here it will launch wedges into the wires in question—as many as eight, if the car has a motor at each wheel, Koepke says. And while Bosch declines to name its clients, Koepke says it’s already in use in cars on the road.
“It’s like a little guillotine.”
Huseyin Hiziroglu, Kettering University
Pyroswitches are relatively common, but this use case is novel, says Huseyin Hiziroglu, an electrical engineer at Kettering University in Flint, Michigan. “It’s like a little guillotine.” One that looks to save lives instead of take them but that delivers the same sort of permanence. The downside of this safety-minded system is that repairing a crashed electric car will involve installing a lot of new wiring. Which means, most likely, spending a lot of money. “I’m sure it will be quite expensive,” Hiziroglu says.
Jason Siegel, a research scientist at the University of Michigan who studies lithium-ion batteries, says pyrofuses “can provide a much-needed safety net for first responders.” But it’s not clear that taking the extra step of severing the wires will change how EMTs and others approach a crashed vehicle, since they won’t know that the little guillotine has done its work. “I don’t see first responders reaching for a [voltage-measuring] Fluke meter to check if the wires are live before cutting when someone is trapped in the vehicle,” he says.
Bosch developed the CG912 semiconductor chip for triggering airbags, but it works just as well for sparking a tiny guillotine to cut an electric vehicle’s high-voltage cables.
There are more than a million electric cars roaming American roads, but, so far, worries around high-voltage crashes haven’t come to fruition. Andrew Klock, who works on EVs and other emerging issues for the National Fire Protection Agency, says he doesn’t know of any first responders who have been zapped. The nonprofit group has trained 225,000 EMTs, firefighters, police, and others to deal with electric cars in the past decade. Relatively simple advice has proven effective. “You just stay away from any broken cables,” Klock says. First responders who need to cut someone out from a mangled vehicle can check the agency’s Emergency Field Guide, which collects and standardizes key information on all the electric car models on the market, to make sure they’re well clear of any cables or components that could deliver a deadly shock. Stay away from those, Klock says, “and you’re gonna be OK.”
Still, as automakers launch an onslaught of high-voltage, battery-powered cars in the coming years—more than 18 million are expected by 2030, by one estimate—more EVs will end up on the side of the road. And for those charged with taking care of them, a little insurance delivered by a little explosion may not be a terrible idea.