For some time past, technical commentators – including me – have been forecasting the arrival of 36/42V electrical systems to replace the existing 12/14V set-up. But now it seems that potential customers have, at best, taken a raincheck on 42V. Why? To quote from a report by auto consultants Frost & Sullivan, “the initial enthusiasm for change has dampened as the high conversion costs became apparent”.

Comments like this have raised a cheer from the opponents of change. What’s wrong with 14V anyway? It has served us well for 50 years with generally acceptable results and everybody knows how to deal with it. One has a certain amount of sympathy with automotive electricians who can see their lives changing dramatically, just as one can appreciate that some of the claims made for 42V – much lighter wiring looms, electric motors a fraction of their current size and weight – are overstated. But the fact remains that 42V is coming. As Frost & Sullivan says, the initial enthusiasm for change has been “dampened”, not extinguished.

More specifically, it has been dampened among the vehicle manufacturers. Their Tier-1 suppliers remain as enthusiastic as ever, not least because the change-up would afford them scope to bring a great many ideas out of the laboratory and into production, to the benefit of their profits. Recent presentations by Delphi and Valeo have underlined the potential benefits of 42V for both cars and commercial vehicles. Their problem is that the arguments are already well rehearsed. We already know there are exciting things which can only be done with a 42V clout: electric power steering for larger vehicles (we already have it in small ones, of course), immensely powerful and efficient combined starter motor/generator systems, engines with electric valve operation and no camshafts.

Pushing the 14V limits

However, we have also seen the vehicle manufacturers push those same suppliers to the limits of 14V capability. It may well be that 42V permits the easy generation of the 5-6kW that many electrical systems engineers would love to play with, while 14V alternators are in trouble producing more than around 2kW. But, say the vehicle manufacturers, at least let’s have those 2kW and see what we can do with that before we take the big jump. Thus we are about to see a generation of cars with the most advanced possible 14V alternators, notable in particular for a switch from air to water cooling (you just can’t take out enough heat with air alone). And experts are already pointing out that on a cold morning, heat begins to flow from a water-cooled alternator much more quickly than from the engine itself; very handy for a quick burst of demisting, especially in cars with common-rail diesel engines, which are notorious – because of their very efficiency – for a low heat rejection rate at low load.

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Just what else can be done with 14V systems, without making the big change? Well, Mercedes has already shown us, first in the SL and soon in other models in its range, genuine “brake by wire” running off 14V. And the Tier 1 suppliers themselves, working with the vehicle manufacturers, have now introduced automatic start-stop systems working with belt-driven high-output 14V motor-generators. In short, the history of the last two or three years is that every time a “killer” application has emerged based on 36/42V, a lot of people work very hard to see if it can’t be accomplished with 12/14V. So far, it has proved (mostly) possible, admittedly by pushing the lower voltage about as far as it is possible to go.

But it cannot go on for ever. Eventually, either the killer application will emerge for which there is no viable 14V answer, or the efficiency argument will prevail. For many in the industry, the key question is not which of those two it will be, but rather when it will happen. The most significant date is the autumn of 2007, when carmakers have pledged to achieve a fleet-average fuel economy figure equivalent to 140 grams of CO2 per kilometre for the 2008 model year. Considerable strides have been made towards meeting that target but there is still some way to go.

Companies with the greatest concern about the situation are those which make the bulk of their money from medium-to-large high performance cars, especially BMW and Mercedes (Jaguar, Saab and Volvo are allowed to aggregate their results with the other European products of their American masters). There are strategies for reducing the fleet average, such as introducing new smaller-size cars like the Mercedes A-class and “son-of-Smart”, and the forthcoming BMW 2-series, and increasing the proportion of diesel-engined cars, which both BMW and Mercedes have done with a will. It seems likely that a gap will remain unless further technical ventures are undertaken. The most likely of these is 36/42V, whose additional efficiency and weight-saving could make all the difference between making the mark and having to do something drastic, like temporarily withdrawing the largest and heaviest cars in the range from the market. 

Implications for economy

It will be expensive, but apart from (potentially) bridging the remaining gap to 140 grams/km it will enable the pioneers to exploit the other advantages of the higher voltage and to present themselves – to an even greater extent than they do already – as the natural leaders in high technology. From that point on, they will be free to use the 42V principle in all manner of ways, and they are certainly preparing to do so. Only yesterday – as I write – I was driving a Mercedes prototype with full “drive by wire” steering, totally dependent on 42V electrics (and also, as it happens, with a new twist on the “active suspension” theme which made similar demands on its hydraulic system). The German executive car specialists are keen to move in this direction and, whatever the cost, will not fight too much against their high-range products going to 42V systems during 2007 at the latest (a year sooner than that might be preferable, to gain field experience and to accustom their service outlets to dealing with the new technology).

Others may be even quicker off the mark. At a presentation just before the end of 2001, Valeo demonstrated a Citroen C5 converted to dual 42/14V electrical system operation, with a 42V air-cooled alternator and a DC-to-DC converter to deliver 14V for those systems which remained standard. The car’s 42V outputs included the engine starter motor (of conventional design rather than in flywheel-integrated type so often suggested), heated windscreen, wiper motor, engine cooling fan, electric cabin heating and heater blower. Naturally, the car had two batteries, one of each voltage – one of the factors tending to push up the overall cost.

At the time, Valeo engineers were keen to stress that a number of options existed when it came to making the voltage change and that dual 42/14V systems could be devised within various cost requirements, and meeting certain limited technical aims. Such a flexible approach means that existing 14V components can be retained except where there is a genuine need to move to the higher voltage, enabling the extra cost of 42V to be taken on board stage by stage. It now seems likely that Valeo will work with PSA in what amounts to a French national project to gain a lead in 42V technology, with a production vehicle – probably of a fairly specialised kind – appearing by 2004.

Expert Analysis

Emerging Developments in Automotive 42 Volt Systems – a focus on materials

The study represents a benchmark look at the implications of 42 volts, with respect to materials.  Forty-two volt technology is evolving at a rapid pace.  Many design concepts are being considered and prototyped.  However, most development work is focused on systems and components rather than on materials in support of these technologies.  Issues are surfacing that need to be addressed and the selection of materials with adequate cost/performance will become increasingly important as 42 V systems penetrate the automotive industry.  This study is the first in a series that will track and evaluate the changes and developments of thermoplastics, thermosets, elastomers and other materials as a result of changing electrical system technology.

Meanwhile, Delphi is pressing ahead not only with systems for cars, but also for CVs. At a recent presentation at its CV electronics unit near Gloucester, the company discussed a range of 42V components and systems opportunities and showed a number of units, including high-capacity alternators and batteries. High electrical output and high efficiency potentially mean even more to CV operators, for whom very often there is a requirement to provide substantial amounts of auxiliary power related to the load rather than the vehicle. Add the fact that system weight saved means additional payload, and that CV operators may take a more rational view of extra first cost if it yields immediate savings in operating costs, and it may yet be that 42V will make its first large-scale appearance in this sector rather than cars.

Sitting at one corner of this argument is the hybrid internal combustion/electric car in all its possible forms. For an “electric heavy” hybrid with electric propulsion and with power coming much of the time from an energy-bank battery, 42V is not enough. These cars, including the existing production examples of the Honda Insight and Civic IMA, and the Toyota Prius, need a 3-phase supply in excess of 100V for satisfactory operation, even though that means taking all the necessary special precautions (which under existing regulations are called for as soon as the voltage exceeds 50) to contain it. But fuel saving opportunities can be created even with 14V components, and certainly with 42V ones.

At the Valeo event, a Peugeot 206 demonstrated satisfactory automatic stop-start operation with a belt-driven 14V alternator/drive motor, claiming a 5% improvement in full-cycle fuel economy and up to 10% in town driving, with the potential for further savings via regenerative braking and optimised energy management. One stage up, Valeo showed a Renault Twingo with an example of the often-discussed “toroidal” starter-alternator integrated into the flywheel. With 36/42V operation, this is a true “mild hybrid” capable of providing electric-motor boost to the engine’s torque output and achieving up to 30% better fuel economy.

Almost all the pressure, note, is coming from two directions: from the Tier-1 systems suppliers, and from legislators tightening the CO2 emission requirements. Overall system efficiency, by whatever means, remains one of the main technical targets in meeting these limits, and the suppliers insist that 42V is an excellent way of achieving it. They have not only the figures to prove it, but – increasingly – fleets of modified vehicles to serve as convincing demonstrators. The target dates may have slipped a bit, but they cannot afford to slip very much more. We may have another year or so of working behind the scenes to optimise solutions and systems, but from 2005 onwards we are likely to see a rush towards the higher voltage. By 2010, a high proportion of new cars, especially at the top of the range, will use 42V for some, if not all of their electrical needs – and the way will then be open to still more technical development.