By Barry Manz, Contributing Editor
[Sponsored by Coilcraft]
As electrification takes over automotive design, efficiency becomes crucial, which has reignited interest in the dual-system approach using 12 V and 48 V.
The auto industry is rapidly moving toward what might be called “total vehicle electrification,” in which everything that can be powered by electricity rather than hydraulics or belts will undergo that transformation. Very simply, engine-driven components powered by electricity reduce the load on the engine, fuel consumption, and thus emissions.
In addition, the increasing number of electronic systems, such as ADAS, employed in vehicles creates higher demand for power. As a result, the auto industry intends to supplement current 12-V power with a separate 48-V system, each one dedicated to specific needs.
The concept of increasing the voltage of electrical systems has been tried before, beginning in the late 1990s. Several factors drove this idea, the first being that as voltage increases, the amount of required current decreases, making it possible to use thinner-gauge wires and smaller motors and other components. In turn, it would reduce size and cost.
Second, the electrical load in vehicles was already increasing every year with the introduction of power-hungry features like heated seats, power windows, electrically adjustable (i.e., motor driven) seats, and other accessories. This began to result in bulky wiring harnesses running throughout the vehicle; boosting the voltage threefold could potentially reduce the size of the cable bundle by 50%.
Initially, the goal was to use two systems, one at 12 V and the other at 42 V, easing the transition from the lower to the higher voltage over time. This would be necessary because making such a change all at once would be a massive undertaking, to say the least. It would place enormous burdens not just on auto manufacturers, but those of test equipment, as well as hundreds of other components in the vehicle.
What ultimately killed off this approach was that the operating life of switches and other components would shrink to the point where they would have to be replaced, probably more than once, over the life of the car, essentially making it a step backward. This and massive retooling, plus other costs, slowly reduced its appeal until it vanished altogether.
Dual-System Redux with 48 V
However, the idea has returned in somewhat different form, this time retaining the 12-V system while adding a separate 48-V system (Fig. 1). It’s the same approach as last time, except the need for separate systems is now far greater, and technologies have dramatically advanced in the last 15 years to make it less costly. Dozens more safety and convenience features are built into vehicles today. And as the industry moves toward autonomous vehicles, that number will rise exponentially over the years as achieving full autonomy requires wireless connectivity, formidable processing power, radar, LiDAR, cameras, and other sensors.
So, recent moves to reign in fuel economy standards notwithstanding, the trend is to increase vehicle efficiency regardless of government mandates or the lack thereof. To achieve this, the industry is moving toward electrification, from various types of gas-electric hybrids ultimately to fully electric vehicles, even though hydrogen fuel cells and other technologies might eventually be competitors.
The current approach uses the 12-V system to power devices such as lighting, infotainment, and other less power-hungry systems, while the separate 48-V system powers start-stop motors, turbochargers, power steering, brakes, air conditioning, and other systems. Together, they will ultimately power all, or nearly all, systems in the vehicle, whether it uses just an internal combustion engine or combine that with an electric motor or motors.
Like its predecessor, this initiative will require huge changes within the industry, but its benefits are potentially large. The roadmap for the future makes a higher-voltage system not just desirable, but a necessity. Several examples help to illustrate these benefits.
Start-Stop and Turbocharger
As time progresses, the start-stop system, formerly called idle shut-off, is being used on more vehicles for its ability to incrementally improve fuel economy. Although it’s a bit unnerving at first, the best systems are almost transparent and will become increasingly so in the future.
To provide this capability, the 12-V starter motor is replaced by a much larger 48-V type called a motor generator unit that uses a 48-V lithium-ion battery and a dc-dc converter. This scenario is (oddly) called a “mild-hybrid” powertrain (Fig. 2), and its champions claim that it can produce two-thirds of the benefit of a full hybrid at one-third of the cost while increasing efficiency by up to 20%.
Electrifying a turbocharger also has significant benefits. For example, turbochargers suffer from turbo lag. Exhaust gases that power the impeller (i.e., the turbine blades) need to increase its speed from a fixed position to between 100,000 and 200,000 RPM as fast as possible, otherwise you have turbo lag.
If the turbocharger was powered by a 48-V system, it could spin up the impeller so fast as to make turbo lag virtually imperceptible. Some automakers are combining this approach with a turbocharger, which is typically driven by a belt powered by the engine. However, in this case, power is supplied by an electric motor. The result is greater power, reduced load on the engine, and better fuel economy.
These are just two examples of how, when electricity replaces the engine as the source of power for an engine component, to achieve significant increases in vehicle efficiency. Major automakers and suppliers such as Aptiv (formerly Delphi) have created their own proprietary solutions that produce even greater benefits to meet future stringent fuel-economy standards while improving vehicle performance. However, nearly all of them require a higher-voltage system to function, so there’s little doubt that 48-V electrical systems are here to stay.
For more information on high-voltage components involved in automotive system design, check out Coilcraft’s application notes.