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AUTOMOBILES WITH 48-volt electrical systems are being seen in some markets as a near-term necessity. In other markets, the unsettled U.S., for example, it’s anyone’s guess.

Automobiles with 48-volt electrical systems are midway, sort of, between conventional internal combustion (IC) cars and full HEVs (hybrid electric vehicles), partway to pure BEVs (battery electric vehicles).

As background, until the mid-1950s most cars, especially in the U.S., had 6-volt electrical systems. The switch to 12 volts back then was based on two trends: more electrical options on cars and the advantage of thinner wiring. As noted in “48 Volts” here at SimanaitisSays, this latter traces back to Ohm’s Law, one of its forms V = I x R, where V is voltage, I is current and R is resistance. In a sense, higher voltage pushes more current through a given-size wire. Or, equivalently, it’s able to maintain the same current flow with thinner (and less expensive) wires.

Twelve-volt systems have been de rigueur since the mid-1950s. Back in (pre-hybrid) 1998, there was talk of going to 36–48 volts, primarily for lighter wiring harnesses in increasingly accessorized cars. This fizzled out with considerations of refurbishing costs and also of safety: An insignificant spark in a shorted 12-volt system is a big deal at 48 volts.

About the same time, along came HEVs. These have dual electrics, 273–300 volts for their hybrid propulsion and 12-volt systems for “hotel loads,” lighting, door locks, etc. By comparison, pure BEVs have voltages in the 330–400-volt range.


Battery suppliers are engineering modular energy storage dedicated to 48-volt systems. This Johnson Controls example uses lithium-nickel-manganese-cobalt cell chemistry. This and the following images from Automotive Engineering, January 2017.

By contrast, there’s the “mild” hybrid, today called the 48-volt hybrid. A mild hybrid can use its added voltage in a variety of ways. The most basic is a start-stop system for its IC engine, actuated when no power is required, at stop lights, for instance. A second enhancement is what’s now called energy recuperation (aka regenerative braking). This returns energy to the battery when the car is braked, or even when it’s coasting down from a given speed.

Note, neither of these concepts involves propulsion of the vehicle as in an HEV. On the other hand, the 48-volt system might drive an electrical supercharger providing forced induction, and higher power, for the car’s IC engine.


This Valeo electric supercharger is used on the 2017 Audi SQ7. Details of the car are at this Car and Driver review.

Another 48-volt variation gives its e-motor direct propulsion responsibility. This might be solely to smooth variations of power during shifts. Or it might convey quick initial acceleration from a standstill.

Or, if sufficiently powerful, this alternator/motor can propel the car in a “coasting” mode: Under easy driving conditions and moderate speeds, the car’s IC engine can be shut down, the steady speed maintained by its e-motor contribution alone.

In the January 2017 issue of Automotive Engineering, published by SAE International, Editor-in-Chief Lindsay Brooke summarized these latest technologies in “Bridging the Power Gap with 48 Volts.” He cites their importance in helping automakers “meet CO2 regulations and satisfy the ‘vampire’ power demands of new electrical subsystems and accessories.”

The prototype Lincoln MKZ he drove had a Valeo North America liquid-cooled belt-starter generator (BSG) incorporated into the IC engine’s accessory drive. Brooke cited other companies investigating such technology: AVL, BorgWarner, Continental, Delphi and Schaeffler.

In Automotive News, February 13, 2017, “48-Volt Hybrids Challenge Europe’s Diesels”, Douglas A. Bolduc shared the views of Schaeffler’s Chief Technical Officer Peter Gutzmer.

Gutzmer said, “I think that in the next 10 years, 48-volt systems will account for the majority of hybrids.” This, because of their relative simplicity and lower production costs, compared to those of full HEVs. He cites fuel efficiency gains of 20 percent compared with a gasoline counterpart and 5–10 percent compared with a diesel.

Schaeffler and Continental have worked jointly in developing the first 48-volt hybrid in the new Renault Scenic and Grand Scenic diesel.


The Renault 2017 Scenic uses a Continental/Schaeffler 48-volt system. The inset shows its e-motor.

The idea of a diesel hybrid may smack of a belt-and-suspenders approach. Even Gutzmer notes, “… but then you have two costly solutions. A gasoline engine with a 48-volt hybrid could offer comparable or better CO2 results than a pure diesel drivetrain.”

At the moment, all this is moot to the U.S. market. The world’s automakers have been working to meet a required 54.5-mpg fleet average target by 2025. Prior to the change of federal administrations, the U.S. Environmental Protection Agency ended this regulation’s midterm review, sort of an “offramp” option to modify it if necessary. However, Scott Pruitt, the new EPA administrator, would just as soon see this agency all but shut down. ds

© Dennis Simanaitis,, 2017

2 comments on “48 VOLTS? (YET AGAIN? OR DIFFERENT?)

  1. Mike B
    February 19, 2017

    Would adding a BSG to an otherwise conventional car really do any good? As a package including a reasonably-sized battery it probably weighs a bit; would the extra weight counteract any improvements in fuel economy? I seem to recall GM doing the BSG thing with the Malibu, and there was a small improvement in gas mileage but not really enough to cover the extra cost.

    I suspect that it would take more than a quickie 48V addon to make a hybrid worth doing. Basically, it needs to produce noticeable horsepower/torque boost to overcome its extra weight, which a BSG can’t really do well. If it were otherwise, wouldn’t we see some aftermarket kits to add it to existing cars?

    • simanaitissays
      February 20, 2017

      Agreed, Mike,
      I suspect each added nuance, regen, electric forced induction, etc., helps the tradeoff.

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