Expect 48 V to have long life in automotive applications

March 11, 2018

Participants in power electronics have been addressing 48-V automotive applications. For example, in January, Analog Devices announced the Power by Linear LTC7821, which the company describes as an industry-first hybrid that merges a switched-capacitor circuit with a synchronous step-down controller, enabling up to a 50% reduction in DC/DC converter solution size compared with traditional step-down solutions. The company said the device is suitable for emerging 48-V automotive systems. And at APEC 2018, GaN Systems unveiled what it calls the industry’s highest current and power-efficient 100-V, 120-A, 5-mΩ GaN E-HEMT device, suitable for 48-V automotive (and other) applications. Also at APEC, Eaton announced its new 3.0-V XT supercapacitor, which offers 15% higher energy density and 20% higher power density at a lower cost per watt-hour compared with currently available supercapacitors, according to the company. Jason Lee, Eaton’s global product manager for supercapacitors, said the new XT supercapacitors are designed for 48-V automotive systems as well as industrial-systems backup and medical equipment.

Given that automotive traction motors require operating levels of hundreds of volts to deliver the required power at reasonable current levels, and that conventional ICE vehicles have operated successfully for years on 12 V, what’s the attraction of 48 V?

Norman Mayersohn in The New York Times has a succinct summary: “Car companies, starting with Volo last summer, have laid out plans to electrify entire lineups of vehicles. But the fine print makes clear that the coming decade and beyond will focus not on just massive battery packs powering electric [traction] motors, but also on adding a little extra juice to the venerable internal combustion engine.”

Primarily, 48-V systems will help efficiently serve new vehicles’ “gadget load,” he writes. But as far as the drivetrain goes, he adds, “…what’s known as a mild hybrid system [offers] the greatest value—up to 70% of the benefit of a full hybrid at 30% of the cost, according to industry analysts.”

It might seem that the move to 48 V should obviate the need for 12-V systems, but that’s not the case. Mayersohn quotes Oliver Maiwald, a senior vice president at Continental, an industry supplier, as saying, “A full switchover makes no sense”—there’s no need to redesign the low-tech, low-cost motors that open windows and adjust seats.

Mayersohn quotes Mary Gustanski, CTO at Delphi Technologies, as saying a 48-V system could boost fuel efficiency 15% at a cost of $650 to $1,000 per vehicle, vs. $3,000 for a full hybrid system, while an electric supercharger can boost torque by 30% for an added cost of $250. Further, 48-V systems could enable electrically heated catalytic converters that reduce cold-start emissions.

But isn’t the 48-V mild hybrid simply a stopgap measure? “It is a reality of how long it takes for the automotive fleet to turn over that really clarifies the picture,” Mayersohn writes. “A forecast by IHS Markit…said 10% of vehicles built around the world seven years from now would have 48-V systems.”

He concludes by quoting Gustanski as saying, “In 2025, more than 95% of vehicles sold globally will still have internal combustion engines. So even in 2030, 48 V will still be part of the mix.”

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