48-Volt Electrical System Could Revolutionize Heavy-Duty Trucks

This story appears in the June 13 print edition of Equipment & Maintenance Update, a supplement to Transport Topics.

Industry exhibitions of trucking technology would not be the same without trucks showcasing components, systems and features intended to hit the road in the future. Some examples of future componentry come to market quickly, others never make it into production. Meanwhile, others represent demonstrations of technology that might be integrated into Class 8 trucks decades down the road.

Romba

One such technology likely to appear soon on one of those trucks is a 48-volt electrical system. Automaker Audi is working on the technology, which will help drive development for car and truck makers alike. While not as “sexy” as an engine boasting higher horsepower and torque, a truck’s electrical system is as fundamental as the powertrain, tires, brakes or wheels.

In fact, a 48-volt electrical system could revolutionize heavy-duty truck systems by helping truck makers increase fuel efficiency, reduce engine emissions and power the continually increasing electrical demands for so-called hotel loads in the cab.

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The shift is foretold in a December report from the Technology & Maintenance Council of American Trucking Associations. The report, authored by TMC’s Future Truck Committee, outlines how the new electrical system will “change the face of trucking.”

It’s been about 60 years since the last major upheaval in the design of a heavy truck’s electrical system. The shift saw the move from 6 to 12 volts. In the 1980s and 1990s, carmakers and industry associations considered developing a 42-volt electrical system. However, that effort never made it to market due to higher costs.

According to TMC’s study, the battery for a 48-volt system would be lithium-ion, the same type used in batteries for mobile phones, laptop computers and gas-electric hybrid cars. The 48-volt battery would be larger than a typical Group 31 lead-acid battery, while being smaller and lighter than four absorbed glass mat (AGM) 12-volt batteries.

Other electrical components — wiring, fuses and connectors — would be about half the size of today’s electrical components. In addition, trucks would have to be fitted with both 12-volt and 48-volt electrical systems, at least during a transition period.

As trucking has added electric and electronic components to vehicles, TMC pointed out the growing electrical current drawn from charging systems continues to grow. The council pegs current peak demand at 5 kilowatts when a truck is parked with a driver resting inside. Through 2030, that figure is forecast to grow an average of 5% per year.

A 48-volt electrical system could provide between 20 kilowatts and 40 kilowatts to power today’s vehicle accessories and tomorrow’s electronics such as electronic data recorders, video cameras, additional electronic system controllers, engine control units and more. In my view, it’s sensible to get this discussion going now because the transition from 12 to 48 volts could take between 10 and 15 years.

Development of a more robust electrical system will allow truck builders to improve fuel efficiency, primarily by reducing parasitic loads on the engine. Also, some of the current emissions controls systems could be driven or assisted by electrical means rather than today’s engine-based methods.

Even though fleets currently enjoy some of the lowest prices for diesel fuel seen in about 10 years, we know the price of fuel will eventually return to levels seen several years ago. A long-range forecast from the U.S. Energy Information Agency predicts $5.15 diesel fuel by 2030, just 14 years from now.

The higher voltage system could support many of the accessory functions currently hung on or in front of the engine. Accessories including the air compressor, power steering pump, air conditioning compressor, cooling fan, water pump and turbocharger could be electrically driven and electronically controlled. On-demand, rather than full-time, use of these components also would likely extend their life.

With increased voltage on tomorrow’s trucks, designers and engineers would have a more robust platform on which to build new engine emission control strategies. Rather than continue on the current path of such strategies, TMC suggested the 48-volt system “would diversify industry efforts to control emissions.” That approach would foster development of new technologies that could reduce regeneration time of the diesel particulate filter, extend cleaning intervals of the DPF or reduce the use of diesel exhaust fluid.

One of the greatest solutions offered by a higher voltage electrical system would be providing sufficient power for “hotel” electrical loads. The current trend of increasing electrical loads used during driver rest periods shows no signs of slowing. Typical devices drawing down batteries when a truck is shut down as the driver rests include cab heating or air conditioning, engine sensors and electronic controllers, interior and exterior lighting, communications systems and in-cab appliances.

When powering those systems, the typical 12-volt Class 8 tractor consumes about 5 kilowatts of power per hour. Assuming four fully charged Group 31 batteries provide about 400 ampere-hours are in good condition, TMC’s estimate shows the batteries would provide 4.8 kilowatts of power per hour. In only one hour, the tractor would not have enough cranking amps to start the engine. A 48-volt system could provide between 20 kilowatts and 40 kilowatts to sustain the hotel loads and provide power to start the engine.

A future truck with more onboard electrical power also could support numerous yet-to-be developed systems such as waste-heat recovery, electro-mechanical valve train, regenerative braking and partial electrification of the air-brake system. Waste-heat recovery recycles exhaust gas energy for various on-vehicle uses such as battery charging.

An electro-mechanical valve train would replace the engine’s camshaft and provide more precise timing of engine valves, resulting in better control of engine combustion to reduce fuel consumption or reduce engine exhaust emissions.

Regenerative braking captures and stores the kinetic energy generated when brakes are applied. Energy stored from braking could be used to reduce the power needed from the engine to accelerate the vehicle, using electric power to supplement diesel power. The use of battery-stored energy through an electric motor uses no diesel fuel and creates no emissions.

However, as innovations are explored for the 48-volt system, several obstacles and risks would have to be resolved. Foremost is the need for two electrical systems on the tractor, at least initially. Even though wiring and connectors would be smaller, the addition of a 48-volt system would require its own battery, starter-generator and several voltage converters. That would add weight and complexity.

TMC envisions voltage upgrades only on the tractor. The industry would continue using the 12-volt seven-pin connector. The 12-volt system on trailers would remain.

Additional issues such as corrosion of 48-volt components and risk of electrical shock would have to be addressed in product design and technician training.

With a 15-year horizon for development of the first 48-volt systems, many advantages can be optimized and disadvantages minimized. But the longer the industry takes to decide on whether to implement the higher voltage electrical system, the more difficult or lengthy the process will be due to continual growth of electronic systems and components on trucks.

Freelance writer Phil Romba has covered trucks and maintenance as a full-time journalist and worked as a public relations manager for Volvo Trucks North America during his 20-year-plus career.