48V Is Coming, and Not Just for EVs

While electric powertrains are driving 48V adoption, OEMs are realizing that xEV and ICE vehicles can benefit from a shift away from 12-volt architectures.

There are two distinct PDNs used in automobiles today. The 12V centralized architecture and fast-growing 48V zonal architecture. The former depends on the thick, 12V wire harness, while the latter draws upon the thin, 48V wire harness, which is far lighter, reduces heat loss and reduces current by a factor of four. (Vicor)

In every corner of the automotive power engineering world, there are discussions and debates over the merits of 48V power networks vs. legacy 12V power networks. The dialogue started over 20 years ago, but now the tone is more serious. It’s not a case of everything old is new again, but the result of a growing appetite for more electrical power in vehicles. Today’s vehicles – and the coming generations – require more power for their ADAS and other safety systems, infotainment systems and overall passenger comfort systems. To satisfy the growing demand for low-voltage power, it is necessary to boost the capacity of the low-voltage power network by two or three times that of the late 20th century. Delivering power is more efficient at a higher voltage, and today, 48V is the consensus voltage for that higher level.

Conversion to 48V systems reduces vehicle total current draw from over 250A to under 75A without impacting the electrical content of the vehicle. Today, most OEMs still use the 12V bus, despite the demand for more current. However, the transition to 48V is imminent and all OEMs have a strategic roadmap to get there in the near future. (Vicor)

The obvious benefits of moving to 48V

Forty-eight volt technology is SELV compliant. It is deemed safe to work with compared to higher voltages. Next, the practical benefits of a 48V power network over a 12V network are rooted in Ohm’s Law, which states that a 48V network will draw lower current than a 12V network to deliver similar power. For example, delivering 1200W of power with a 12V network requires 100 amps, while a 48V network will require only 25 amps.

This basic advantage drives a large number of vehicle-level benefits.

More tangibly, the 48V network will use a smaller-gauge wire than 12V, and it will have higher electrical efficiency. So not only will the wire harness weigh less due to lower copper content, but the higher efficiency will allow more power to reach the load. In a vehicle, the primary power cables can be reduced from a 4-gauge wire to a 10-gauge wire, which will reduce copper content by over 70%, driving substantial cost savings. The 10-gauge wire is also at least 67% smaller in diameter, yielding large efficiencies in wire routing and installation efforts. And of course, there are wire harness weight savings of up to 80% in the transition from 12V to 48V. This can be substantial, ranging from 5 to 10 kg (11 to 22 lbs), depending on vehicle size and content. This makes the 12V to 48V conversion a rare triple win for the vehicle team. It’s lighter, easier to assemble and costs less.

12V and 48V power systems compared: a power system configured for 48V offers current-carrying capacity, wire size, harness overall weight and power dissipation improvements over 12V power systems. (Vicor)

There are also point-of-load benefits for the various devices that are consuming power in the vehicle. 48V motors draw lower current for the same power, making them more efficient and reducing the heat generated and wasted by the motors. This results in lower operating temperatures and gives engineers the ability to downsize the devices themselves, again saving volume and mass. Similar reductions apply to all of the motorized loads in an automobile, so the savings cascade across the vehicle when converting to 48V.

48V is not just for EVs

Point-of-load converters like the DCM3735 in a zonal architecture bridge the 48V to 12V gap, allowing OEMs to reap the benefits of an upgraded power system without forcing a simultaneous redesign of all 12V loads. (Vicor)

The transition to 48V has been primarily driven by the growing electrification of the automobile. Mild (start/stop) hybrids, hybrids and plug-in hybrids all utilize some 48V circuits for the high-power loads in the vehicles. EVs need to step down the high-voltage battery, and 48V is a natural bridge used by many other electrical applications. EV-only manufacturers are leading the adoption of 48V power networks, but legacy OEMs building a mix of ICE, hybrid, and all-electric vehicles have also investigated the merits of 48V.

Legacy ICEs with 12V alternators have cost-optimized hundreds of high-reliability devices used in the vehicle, providing a highly effective turnkey power system. Today’s alternators are designed to supply between 65 and 130 amps, limiting the available power to under 2.0 kW, however. With the larger electrical loads coming into the newest vehicles, the 12V alternator falls short of current and power demands.

Today, OEMs have to design power controls that shed loads during high power consumption events. For example, a pickup truck with a plow system will need to shed seat and window heating loads in order to operate the plow hydraulics. Given these types of trade-offs and the work associated with designing these power management systems, switching ICE vehicles to a 48V alternator makes more sense. It meets the demand for increased power and enhances overall efficiency. OEMs have seen what 48V can do for EVs. Now, they are smartly contemplating the benefits of switching to a 48V alternator for their ICE platforms.

48V zonal architectures are the bridge to the 48V world

The top obstacle to fully converting a vehicle from 12V to 48V has always been the hundreds of 48V versions of power loads that would need to be created and validated. With a critical mass of vehicle power loads exceeding 2kW and pushing 4kW or more, the benefits of going to 48V are reaching the tipping point. To accomplish this changeover without overwhelming suppliers and engineering departments, the 48V zonal architecture has become the bridge needed to cross the chasm.

A 48V zonal architecture allows for the primary power generation and bus to change to 48V, while maintaining a mix of 12V and 48V devices. Primary power networks designed as 48V systems reap the primary cost and weight savings from downsizing the power cables from 4 to 10-gauge wire. It also supports the necessary increase in power to feed the many new and power-intensive systems in today’s vehicles.

The 48V zonal architecture borrows heavily from the zonal controller architecture that is being implemented by many OEMs to decrease the number of IC controllers in the vehicle. In fact, the 48V zonal architecture complements this controller architecture.

New, micro-sized DC-DC converters, such as the NBM2317 and DCM3735 from Vicor, are added to the zonal controller board to create a local 12V network, allowing for a mix of 12V and 48V loads in the controller’s zone. It’s also possible to deploy these miniaturized DC-DC converters to the point-of-load, independent of the controller. Deploying the 48V-to-12V conversion to zonal ECUs or points-of-load creates a future-proof architecture. As more 12V

loads are changed to 48V, the local 48V-to-12V converters can be removed, until the entire vehicle has fully converted to 48V loads. This gives the OEM control over the pace of adoption, so that engineering workload and validation budgets can be managed. This will be especially helpful as ICE-based powertrains adopt 48V alternator-generators and OEMs ramp-up demand for large volumes of 48V devices. The rate at which both ICE and electrified platforms converge on a uniform 48V architecture will undoubtedly accelerate in the coming years.

48V is the new 12V for xEV and ICE

The automotive industry is currently crossing the chasm from 12V-based power architectures to 48V architectures. In order to reach the other side (a fully 48V power system), OEMs will use the zonal architecture as a bridge. This enables easy, self-paced passage that balances the technical benefits, cost savings and engineering resources. The zonal approach capitalizes on the significant design and weight benefits while allowing the OEM to move at a cadence that suits their business strategy. Thinner gauge wires, miniature DC-DC converter modules and downstream consolidation enable incremental space and weight savings while decisively upgrading power and performance. The 48V zonal architecture, leveraging high-density power modules, is easy to design, scales effortlessly and has few tradeoffs. It is the fastest path to 48V, and it delivers an immediate productivity boost.

Greg Green is director of Automotive Marketing at Vicor.