48 Volts: Time for a Jolt to Vehicle Performance?Winn Hardin | September 03, 2015
It was an idea that emerged in the 1990s with the increasing electrification of internal combustion engine automobiles. As more electric motors, telematics, entertainment and other electronic systems were designed into cars, engineers found themselves knocking against the limitations of a 12 volt (V) battery-fueled electrical system.
In response, carmakers proposed a 42 V standard that would allow designers to cut wiring harnesses’ weight by one-third to offer more power for electrical systems and make vehicles more efficient. However, the proposed new standard never caught on.
Indeed, 42 V for automobiles shorted out for multiple reasons, says Christian Müeller, manager of Europe component forecasts and analysis for IHS Global GmbH. For one thing, “the generators got a new lease on life being water cooled and more powerful,” he says. Furthermore, head lamp filaments were not compliant with the higher voltage, among other issues.
Fifteen years down the road and the same problems are reappearing. Cars need more electricity, he says. In the upper segment, luxury vehicles that are fully loaded with options can require up to 11.5 kW of power. “An alternator delivers 1.5 kW of continuous power and peaks at 3 kW,” he says, “so you see the gap.”
However, it is not just luxury vehicles and optional electronic systems that are running out of power. Speakers at the Société des Ingénieurs de l'Automobile’s ICE Powertrain Electrification & Energy Recovery conference in May 2013 said that some 70% of new cars introduced in Europe in 2020 will need electrification to meet the European Union’s (EU) goal of 95 g/km of carbon dioxide emissions. “And synonymous with electrification will be the 48 V power-net,” says Peter Els, an automotive engineer who worked for Nissan in South Africa and now covers the automotive industry for Automotive IQ.
“Unlike past developments whose pace was largely dictated by the OEMs and available technology, the timing of 48 V is largely being determined by emission and fuel consumption requirements,” Els says. Increased levels of electrification require power far beyond the present on-board 5 kW. Start-stop systems already push 12V technology to the limit. However, with further electrification required for implementation with mild hybrids, this will need to increase to approximately 10 to 15 kW.
“At this level,” says Els, “with a 12V system, 1000 A of current would be required, which would need power cables with diameters of 10 to 15 mm—heavy, costly, difficult to manufacture and install.” Using this model cable resistance would result in significant losses according to P = R I²,” which is Ohm’s law.
Under current European regulations, by 2020 carmakers will pay penalties for vehicles that exceed 95g/Km of CO2. Avoiding these penalties will help to fund the development of new 48V power electronics and compatible electrical systems, which will help carmakers meet new emission regulations.
According to Dr. Wolfgang Bernhart, an expert in electrified powertrains at Roland Berger Strategy Consultants’ Automotive Competence Center, recovering energy during braking or deceleration with 48 V is twice as efficient compared to 12 V. He says, “If you can save 5%-10% with 48 V, you could only save 2.5% to 5% with 12 V, and [additional power for] boosting would be zero.”
Core to the 48V efficiency debate are systems such as torque assist reversing alternators (TARA). “Alternators generally work in one direction,” says Dr. Peter Harrop, chairman of independent market research and business intelligence firm IDTechEx. “You take your foot off the accelerator and the alternator charges the battery.”
Nevertheless, an alternator is a rotating machine, so it can be designed to act as both generator and a motor. Similar to regenerative braking for electrical vehicles (EVs), with a decent battery you can directly couple to the TARA and regain more electricity during braking, Harrop says. “Indeed when the engine needs a bit more effort, you can mechanically push the vehicle—thus the terminology,” he says.
Massachusetts Institute of Technology spin-off Levánt Power has developed GenShock, an active suspension system for automobiles and trucks that uses electrical power to proactively adjust the suspension while also using the natural motion of the suspension system to replace the electricity it uses, says IHS’ Müeller. “But these systems need 48 V to operate.”
Component Challenges Remain
While a new 48V automotive electrical standard could reduce a vehicle’s weight and make vehicles more efficient, the industry could not adopt the new standard currently even with 100% consensus.
For example, new DC/DC converters would be needed for OEMs that chose to have both 12 V/ and 48 V nets in the vehicle. New 48 V power inverters would need to be developed along with electronic control units (ECUs) that are 48 V compatible.
While 48 V would allow for smaller, more efficient electric motors inside the vehicle, higher voltages would require larger diameter copper wiring for the wiring harness, canceling part of the lightweight benefits in other areas of the car. A move to aluminum would save more weight, but brings its own challenges. Moreover, newer hybrid wires that use carbon nanotubes for more efficient electricity transport are still in development.
“Recent development of low-cost composite wires with high strength and ultra-high conductivity has drawn considerable interest as an alternative to pure copper,” says Els.
Several research groups, such as the Materials Genome Initiative (MGI), have succeeded in imbedding nanoscale graphitic carbon (for example, carbon nanotubes, graphene nanoscrolls and so on) into copper and aluminum matrices.
“They report very high electrical conductivities—as high as 1,000% IACS—and strengths as high as 350% that of oxygen-free high-conductivity (OFHC) copper,” Els says. “This could allow the reduction of the weight of the wiring harness by up to 25% without sacrificing performance.”
Relay, switch and conductor arcing are also problems that need to be addressed. While 48 V was chosen specifically to stay under additional international electrical safety regulations for 60 V and higher systems, dangers remain. Recent research shows that the 48 V arc energy is 50 to 100 times higher than in a 14 V system, according to Els. Such arcing can generate temperatures up to 1000°C and ignite fuel vapors, start a fire in plastic insulation and even melt metal.
“Simply redesigning relays, switches and fuses for higher voltage and using flame-retardant materials is not a total solution,” he says.
EV, Hybrids and Global Momentum?
One might assume that growth in the EV market (which regularly operates at 200 V and use power networks upward of 700 V for some military and experimental vehicles) would help traditional ICE car manufacturers develop the components and infrastructure necessary to make 48 V efficiency a reality, but not so fast, says Müeller.
“There really isn’t any carryover between EVs and 48 V,” he says. That is because the EU’s SAFEDRIVE program, which has developed a series of EV building blocks for small manufacturers, is not expected to have an impact on the larger automotive market.
Currently, Europe is leading the way in the development of 48V systems, with the first commercial vehicles hitting the road in 2015 and 2016. Müeller estimates that the U.S. is three years behind Europe, and Japan is one to two years behind the U.S.
“A 48 V standard is pretty much a European topic,” says Müller. “Audi is expected to launch a car [in 2016], but most of the move towards 48 V has not hit the market yet. U.S. manufacturers are all looking at 48 V, led by their European derivatives, while Japan with its small K cars and city driving wants to extend 12 V as long as possible.”
In order for 48 V to really work, it has to be embraced globally, not only for the rapid deployment of the technology, but also the economies of scale, says Els.
Although SAE has published several papers and convened many conferences around the topic, he says that to date the body has not formulated many norms.
“I think that it is essential to standardize at least the voltage ranges of 48 V systems,” Els says. “This is one of the major goals of the LV148 and should not be altered,” he says. In order to obtain a standard voltage level in the worldwide automotive industry that will be established like the common 12 V level years ago, it is important to use the same standards.
This standardization helps both the OEMs and the suppliers design systems on the same voltage level and reduce their costs, and to achieve that, Els says, “without giving up their individuality.”