Within a decade’s time we will probably have very different electrical systems on trucks than those in use today. Electrical demands on today’s highway trucks have pushed systems to their capacity. Current electrical demand on a typical on-highway truck is about 3-5 kW, but that is projected to increase to 40 kW by 2030. Development of advanced powertrain technology is stalled because of capacity constraints. There’s much more we could be doing with electricity if the systems were up to it.
In short, we need to upgrade our electrical systems. But do we migrate up to 24 volts or 48?
“I don’t think the industry has converged on 24 or 48 volts at this point,” says Craig Jacobs, Eaton’s director of engineering and program management for Controls & Protection, Transportation, Military and Aerospace Division. “There are a couple of different camps on this. The 24-volt supporters point to Europe where 24-volt systems are used, so there’s already some standardization and components are readily available. The 48-volt camp says if we’re going to make a change, let’s go all the way.”
Jacobs says 24 volts might take us out 10 or 15 years, but then we’d be at capacity again, with very limited potential for expansion. “Going right to 48 volts would last longer before having to upgrade again. It also gives OEMs a lot more flexibility in how they design vehicles.”
The Australian trucking industry uses both 12- and 24-volt electrical systems because they use both European and North American equipment. Mathew Jenkins, global engineering and sales director for lighting system supplier, Optronics International, is based in Australia, and has some first-hand experience using both systems.
“Australia leans to the 12-volt architecture,” he says. “Our trailers are 12-volt, but some of our [power units] are 24-volt. That forces us to deal with reducing voltages, but that is fraught with other problems.”
Voltage reducers are not linear, he says. They will take 24 volts and turn on and off very quickly, producing an average voltage of about 11 volts over time. “That’s very much like how an AC circuit works, so devices like electronics, motors, LED lighting, etc. do not respond well to that sort of signal. Voltage-drop over distance, like with our multi-trailer road-trains, makes it even more problematic.”
In North America, we can avoid those challenges, making the jump only once — if it’s carefully orchestrated.
“As an industry, we should have gone to 24 volts years ago,” says Bruce Purkey, chief creative engineer at Lowell, Arkansas-based Purkeys Electric. “We’d be further ahead than we are today, but we’d still be close to the same capacity limits on the system. 24-volt systems would still not be up to some of the advanced technologies engineers are talking about today.”
Purkey suggests going to 24 volts would help, but it would be costly and of limited value in the long run because of future demands on the system.
“When one looks at mild hybrids and the likes, 48-volt electrical systems for accessories can be desirable,” says John Bennett, general manager of global product strategy and advanced engineering for Meritor. “They will require roughly four times less current than a 12-volt system, reducing the amount of copper required and reducing costs. With mild hybrids, 48 volts could also mean all electrified components operate at the same voltage, simplifying the system.”
Hurdles for 48-volt migration
Systems operating at 48 volts would open up huge possibilities for fuel savings and emissions reductions while fundamentally transforming the basic vehicle electric and electronic (E/E) architecture and the way Class 8 trucks are designed and built. Switching to 48 volts would probably take close to a decade and would come with a long list of challenges. But that list would still be significantly shorter than the list of opportunities.
In December 2015, the Future Truck Committee of the American Trucking Associations’ Technology & Maintenance Council issued a discussion paper on the topic, Exploring the Potential for 48-Volt Commercial Vehicle Electrical Systems: Changing the Electrical/Electronic Face of Trucking.
In it, the authors outlined some of the challenges:
“While 48 volts is not far from 12 volts in physical terms, real world issues are a cause for concern. Current 12-volt designs won’t automatically work at 48 volts; even simple fuses will not migrate, let alone dimmers and active load controllers. Some fuse panel and harness makers have found that common 12-volt mini- and maxi-fuses do not behave properly at 48 volts. They can fail to interrupt excessive currents properly, causing serious overload conditions. Also, interconnection technologies have evolved for optimal cost and performance in a 12-volt environment. The present design of connectors, circuit breakers, and relay contacts may not be optimal at 48 volts. Therefore, manufacturers must re-evaluate component suitability for the higher voltage...”
As Purkey puts it, “at 48 volts, none of the electrical components we use today would work anymore. They will all have to be redesigned, tested and approved for the higher voltage. But once we get to 48 volts, there’s almost no end to what we can do with emissions reduction and fuel efficiency.”
Changing to 48 volts would have profound implications for almost every component supplier at every level, from the OEM all the way through to aftermarket. For technical reasons, the components will need to be almost impervious to damage and electrical shorting. They will need more robust insulation, different contacts and wholly different designs. They would need to develop a coding system where 48-volt parts are readily distinguishable from 12-volt components. Systems will also have to be designed with fail-safes to ensure that inadvertent use of the wrong parts, or improper connections — jump starts, for example, or drivers hooking up their own electronics — do not cause catastrophic damage to other parts of the system.
Since they will be handling higher voltage, the components will experience greater electrical stress, and will therefore be likely to wear out sooner. They will also cost more. But that’s not the end of it.
“When you increase the voltage by a factor of four [from 12 to 48], you’ll increase the potential for corrosion in the system by a factor of 10,” says Purkey.
Any moisture wicking into a connector will kill that circuit 10 times faster than today, so that will call for impermeable connectors and lots more training for technicians on how to work with 48-volt systems.
That’s a daunting but far from complete list of the challenges of moving to 48-volt systems. You may think, do we really want to go there? Experts agree that it’s not only inevitable, but the sooner it happens the better. The TMC paper suggests that the time is right for this sort of a move because truck designs in other parts of the world are facing similar electrical shortcomings.
“Such a move on a world-wide scale would uniformly advance automotive electronic technology and achieve, for the first time, a global truck design, since both the Western European 24-volt system and the North American 12-volt system would likely be superseded simultaneously.”
With all those challenges, why would we want to move to 48-volt systems?
Unless you understand the basic principles of electricity, it might seem counterintuitive that you can use thinner wire and smaller components with 48 volts as opposed to 12, but that is in fact the case. When you double the voltage, you reduce the current by half. If you quadruple the voltage, you cut the current by a factor of four.
Headlight wires, for example, could go from the present 12-gauge to a much thinner 28-gauge. High-amperage cables like those on starters and alternators could similarly use much thinner cable. “In transmissions at 48 volts, we could use smaller and lighter actuators that are actually more powerful,” says Jacobs.
The same goes for things like fans, compressors, pumps, etc. To comprehend the benefits of using 48 volts rather than 12, you have to re-imagine the heavy truck powertrain.
For example, we presently use a big broad or tall radiator mounted in front of a giant engine-mounted fan. Beside the engine we have components such as alternators, AC compressors, power-steering and coolant pumps. They are placed there only because of the proximity to the gear train on the front of the engine.
If the radiator could be moved to a side position on the truck, with the big cooling fan replaced by several smaller electric fans, you eliminate the need for a large, relatively square front to the truck. All the pumps and compressors we drive off the engine today could be replaced with electric pumps and located elsewhere on the chassis and controlled so that they operate only as needed. That nearly eliminates the need for the drive mounts on the front of the engine, while reducing the parasitic losses associated with turning compressors, fans and pumps that not in use. With electric air compressors or power steering pumps, you energize them only when there’s demand. And that power comes not from the engine, but the battery.
“If you take a lot of that stuff away from the front of the engine, it would give the OEMs a lot of freedom they never had before to redesign the front of the truck,” Jacobs says.
Taken to its ultimate potential, as explained in the TMC paper, it’s likely that we’d see engine camshafts disappear, replaced by electro-mechanical valve actuators that would give very precise and independent control of the operation of the intake and exhaust valves to optimize the combustion process. It could also facilitate a sort of internal EGR process where not all the spent gas is ejected from the cylinder before the next intake stroke, eliminating the need for troublesome EGR valves and coolers and the associated plumbing.
Here are just some of the other potential innovations that will come with 48-volt electrical systems and the off-boarding of current engine-mounted components:
- Smaller and lighter HVAC systems that can be packaged independently of the engine, likely leading to a single set of evaporators and condensers, rather than the separate cab and sleeper systems used today.
- Integrated starter/generator units, likely built into the transmission, can provide much more efficient power generation than current belt-and-pulley systems while being unobtrusively packaged. Because the transmission is always turning while the vehicle is in motion, it allows for energy generation even if the engine is not running, as could be the case in coasting situations.
- Electric turbo-compounding could use a high-speed generator built into the compressor side of a turbocharger to generate electricity to charge batteries.
- Hybridization through electric motors in the drivetrain, or as some manufacturers like Dana, Meritor and others are thinking about, electric-powered drive axles in a 6x2 arrangement.
Ryan Laskey, vice president, driveline and commercial vehicle engineering at Dana Inc., sees 48-volt architecture lending itself to hybridization of on-highway trucks as a bridge between diesels and pure battery-electric vehicles.
“We see axle-mounted electric propulsion units possibly acting in a start-up or boosting application with downsped drivelines,” he says. “That would take some load off the engine, possibly opening the potential for lower horsepower engines or another source of tractive effort in a 6x2 setup. Bear in mind that such a system would be used only for short periods of time as needed, not run constantly, so the 48-volt architecture would support that kind of application.”
We haven’t discussed batteries here, but the size and type of battery used with a 48-volt system will have a major bearing on how this advanced technology works. There are several technology contenders, including lead-carbon, nickel-metal-hydride, lithium-ion, lithium-polymer, carbon nanotube and even lead-acid. Depending on the 48-volt method used, it could consist of a 48-volt battery source and E/E system, one 48-volt battery source and one 12-volt battery source with two E/E systems, or one 48/12-volt battery source combination and two E/E systems, notes the TMC 48-volt discussion paper.
While a wholesale switch to 48 volts could take a decade, some of the technology may be here much sooner than you think.
“Eaton is working with a couple of major OEMs now, and we’re tentatively targeting some of this technology for production in 2021,” says Jacobs. “There are really no technical roadblocks to implementing it. We want to ensure the technology is ready for the market and the market is ready for the technology. It’s a major change.”
Major indeed, especially when you consider the impact on the supplier side of the industry. Still, it’s all part of the evolution of the heavy truck powertrain, and it should all prove beneficial in the long run, even if it is expensive.
“There’s opportunity ahead of us to harvest more energy as efficiently as possible from smaller or less-polluting engines,” says Optronics’ Jenkins. “We need to understand the reason for the change, and that the change is for the positive. It’s for our futures and for the environment; it’s not just for the sake of change.”