A Brief History of 42V

In 1994, at the initiative of Daimler-Benz, the first "Workshop on Advanced Architectures for Automotive Electrical Distribution Systems" was held at the Massachusetts Institute of Technology Laboratory for Electromagnetic and Electronic Systems (MIT/LEES) in Cambridge with the aim of defining the architecture for a future automotive electrical system. From the outset, the participants in this workshop included suppliers as well as the automobile companies Daimler-Benz, Ford and General Motors.

In September 1995, various electrical systems architectures were compared at MIT using the tool "MAESTrO", and in December 1995, in the "Conclusions" of this study, a future voltage level of approx. 40V was defined.

In early 1996, the "Consortium on Advanced Automotive Electrical and Electronic Systems" was set up. At the ensuing workshop in March 1996, the future nominal voltage of 42V was laid down.

In August 1996, IEEE Spectrum published the paper "Automotive electrical systems circa 2005".

On the occasion of the October 1996 Convergence in Detroit, Professor John G. Kassakian (MIT) gave a talk entitled "The Future of Automotive Electrical Systems" as part of the "IEEE Workshop on Automotive Power- Electronics".

On March 24th, 1997, Daimler-Benz presented the "Draft Specification of a Dual Voltage Vehicle Electrical Power System 42V/14V" to the MIT.





General Motors


At the same time as the activities in the USA, in 1994, again at the initiative of Daimler-Benz, the former SICAN GmbH held its first "Forum Bordnetz" (Vehicle Electrical System Forum) in Hanover for German automobile companies. Here too, suppliers were invited to participate at a very early stage, together with all European vehicle manufacturers.

On February 15th,1996, the introductory paper "Bordnetzarchitektur im Jahr 2005" (Automotive electrical system architecture for the year 2005) was agreed, and on June 4th, 1996, BMW presented the "Tabelle heutiger und zukünftiger Verbraucher im Kfz" (Table of present and future loads in the motor vehicle) and the "42V/14V-Bordnetz" (42V/14V PowerNet).

On September 13th, 1996, at the 7th International Technical Meeting for Vehicle Electronics in Baden-Baden, considerable interest was raised by the paper "Neue Bordnetz- Architektur und Konsequenzen" (New Automotive Electrical System Architecture and Consequences), presented by Dr. Richard D. Tabors (MIT).

On March 6th, 1997, BMW presented the "Spezifikationsentwurf für das Zwei-Spannungsbordnetz 42V/14V" (Draft Specification of a Dual Voltage Vehicle Electrical Power System 42V/14V) in Hanover.

The work at SICAN GmbH was given decisive impetus by the cooperation between BMW and Daimler-Benz, as witnessed in their joint definition of the European "Load List 2005" and the jointly authored "Draft Specification of a Dual Voltage Vehicle Electrical Power System 42V/14V".


Forum Bordnetz






After extensive preparatory work, resulting in the "List of Loads in the Automobile of the Year 2005", various automotive electrical system architectures were compared using the tool "MAESTrO" (12V, 12V/24Vdc, 12V/48Vdc and 12V/60Vac) in the September 1995 workshop at the Massachusetts Institute of Technology (MIT/LEES). The finding of this study was that the highest possible direct voltage was the best alternative.

The limiting factor for direct voltages is a shock-hazard protection limit of 60V, which must not be exceeded even during voltage fluctuations caused by extreme conditions. This limit eliminates the option of an automotive electrical system with a nominal battery voltage of 48V, because at low temperatures the charging voltage of the battery can attain 60V. Also, the price, weight and volume of batteries are influenced by the number of cells, which must therefore be kept to a minimum.

New battery technologies for automotive applications would not have been available at affordable costs for the 42V/14V PowerNet. They require a special recharging system and are therefore not operable "rigid" to the vehicle electrical system, as is advantageous for covering power peaks. Lead-acid batteries are low-priced and have a very "compliant" charging/discharging characteristic. Therefore, lead-acid batteries would have been used optimised for energy and service life at the lower voltage and optimised for power at the higher voltage.

Another important criterion for a new architecture was that it should offer extensive migration possibilities, i.e. the loads should if necessary be converted to the higher voltage only gradually as a function of actual requirements.

For the sake of clarity, it is necessary to understand that the present 12V automotive electrical system has an alternator/regulator voltage of 14V, and that 14V is therefore the dominant voltage. Consequently, in the future automotive electrical system the name of this branch has been corrected to 14V.

Depending on operating conditions, the vehicle electrical system voltage today can vary between 6.5 and 16V, with a varying degree of ripple superimposed on this value. In the 42V/14V PowerNet the 14V branch should have been freed of higher-power loads and should therefore be confinable within much narrower limits.

Power electronics is becoming increasingly important in the automotive sphere and will be a decisive factor in the price of future vehicles. This criterion was therefore especially important when selecting the most suitable higher voltage level. Despite the considerable upward trend of power electronics in automotive applications, its share of the market will decline, because growth rates in other market segments are even higher. For that reason alone, a specific manufacturing technology for automotive use is inconceivable.

Choice of voltage

In intensive discussions with the major semiconductor manufacturers, a voltage of approx. 40V was found to be advantageous. Many arguments are summarised in the paper "Intelligent Power Semiconductors for Future Automotive Electrical Systems" presented by the former Siemens Semiconductors now Infineon at the 17th "Elektronik im Kraftfahrzeug" (In-Car Electronics) conference on June 3rd/4th, 1997.

Other arguments for a higher voltage included the reduction of weight in the wiring system and the improved stability of the automotive electrical system, including by means of reduced voltage drops. With three times the voltage, thick conductors can be reduced to a third of the cross-section, and at the same time the relative voltage drop can also be reduced to a third. For the same cross-section, the relative voltage drop is now no more than one ninth.

The voltage level resulting from these comprehensive arguments was so close to three times the present voltage that 42V became the automatic choice for the second voltage level.



As one of the "fathers" of 42V I vehemently advocated the naming of 42V/14V for the new PowerNet unlike 36V/12V. After I was interviewed by Paul Hansen, the editor of the Hansen-Report, my explanation was placed on the front page of the Hansen-Report in April 1998:

Dieter Blauensteiner of Daimler-Benz's research operation explained that the present voltage is not really 12 volts: "The nominal voltage in today's vehicle is around 14 volts [voltage while your engine is running] - that's also the nominal voltage of the alternator, and 14 times three is 42."

Regarding the hight of the voltage it was hawked, that 42V would have been the Answer to the Ultimate Question of Life, the Universe, and Everything.

Others joked because the 1st International Congress on 42V PowerNet held in the Congress Center Villach/Austria on September 28-29, 1999 used the phone number 04242 42000, fax 04242 42000-42.

The Ultimative Question

Originally the implementation of the Dual Voltage 42V/14V PowerNet was planned for 2005. It was obvious that the new development of 42V components would cause adequate costs. The suppliers heavily under pricing pressure by the automobile companies for the 14V components hoped for improvement of their margin at 42V. Finally no automobile company wanted to bear the numbered additional costs for the change. The activities concerning 42V are meanwhile suspended.

Present State