Vehicle 42 Volt Electrical Systems Seminar

20th January 2004, Cranfield University Library, Cranfield, UK 


Presented by Peter Hartnett, Transparent Engineering




In the last few years there has been a growing body of opinion in the automotive industry that the 14V vehicle network is approaching the end of its capabilities for higher power applications. A number of organisations, including a consortium of automotive OEM's lead by MIT, have proposed a transition to a 42V vehicle network. Many automotive manufacturers and their suppliers have started extensive studies on the subject and a number of vehicles with 42V applications are becoming available.


However, the transition to 42V is an enormous undertaking. In the extremely cost sensitive automotive industry, such a move can only be justified if it makes economic sense and provides a competitive advantage.  This talk presented some of the technical arguments for a 42V network. It also examined the commercial implications and discussed the manufacturer’s present status.  




Consensus among automotive OEM's and suppliers towards the end of the 1990's was that 14V cannot support future on-vehicle power demands.  Today some suggest this is not necessarily the case and that 14V is good economic solution.


Vehicle power requirements have shown an increase in on-state peak power demand in-vehicle from 12kW in 1996 to 23kW predicted for 2005 models.  At the same time these vehicles will require environmental improvements, primarily exhaust emissions and fuel economy.  Present alternator technologies can provide around 2kW for advanced devices with water cooling.  In some vehicles multiple generators and batteries are already in use.  Much of the 42V effort so far expended has been aimed at generator technology, including combining starter and alternator into a single integrated starter-alternator (ISA) machine that would be crankshaft mounted.


Peter Hartnett explains the power systems 

architecture for a mixed 14V/42V vehicle.

Why 42V?  A few years ago it was additional functionality and combining systems (such as ISA) that 14V technology could not cope with due to the power levels (hence currents) required.  Today emissions regulations (low and near-zero requirements) are the primary in-vehicle driver.  Soft hybrids, combining an electrical motor-assist with internal combustion engine (ICE) have proven to help meet these emissions requirement.  These soft hybrid vehicles can also take advantage of newer technologies including regenerative braking, stop-start capability (stopping the ICE in traffic for example and running on the electrical assist), electric power valve train (EPVT) etc. 




System architectures originally proposed include mixed 14V/42V system.  This allows safety critical features to be implemented as there is potentially a redundant power system available on-vehicle.  Migration from 14V to 42V was expected to eventually be complete some years ago with the mixed systems offering an interim method of technology transfer.  These mixed systems require a new product to the vehicle system, a voltage converter (DC-DC) transferring power between two electrical power networks.  The DC-DC converter offers no function to the user and OEM's would be expecting to add this at very low cost, approximately $0.05/W for a 1kW device.


The ISA device can also add further features such as damping (ISAD) by electronic control of a 3-phase asynchronous motor mounted directly on the engine crankshaft (in place of the flywheel).  This type of motor can also provide an electrical boost function.  Higher power motors and electronics also have inherent limitations, powers above 20kW make heat dissipation and cooling a challenge.  Despite these challenges there is expected US production in 2005 of a  GM pick-up truck featuring an ISA system and almost all electrical systems running from 42V, the vehicle will also offer a dual 120Vac, 60Hz household style outlets!




Introducing any new technology is especially challenging in the conservative automotive industry.  A replacement power network is even more so due the radical nature of the change and existing base of 14V systems in use.


Energy storage media (i.e. batteries) are expected to remain lead-acid technology due to cost, reliability and recycling, plus they offer very good temperature stability and are a proven automotive technology.  


Jump starting is a serious safety challenge due to potential interconnect between different vehicle power networks.  Solutions include completely removing the option of jump starting, providing a standardised electrical interface and  mechanical interlocking system.  All these solutions have no added value or function under normal operation of the vehicle.  


An arc can self sustain at 42V and be a potential fire hazard, hence current fusing methods and technology is inadequate.  There is a need for new materials for fuse blades and their mechanical support


Light sources on a vehicle are a high power consumer with a very low on-cost.  42V DC lighting with thin filaments give short life in a vibratory vehicle and at high cost.  The proposed solution is PWM control for existing 12V bulbs, but this adds on-cost in the control although permitting bulb technology retention for the end user.  PWM could improve bulb reliability and has been proven to have no detrimental effect on bulb longevity. 


Voltage conversion is another issue to be resolved, not just 42V to 14V, but also at the board level; 5V, 3.3V 1.8V. Linear regulators are no longer viable at 42V input due to heat dissipation, hence more Switched Mode Power Supplies (SMPS) will be required.  SMPS techniques are not well established in automotive industry and have perceived reliability, space, cost and  EMC issues.  


The EMC performance of the vehicle itself will change at 42V.  The associated test standards will require some changes, mainly to conducted immunity levels, other standards can be applied "as is".  Meeting the standards may prove more difficult with the increased use of SMPS and PWM techniques.


Supply Chain 


The size of the automotive supply chain can be daunting and similarly the challenge for 42V is enormous and may be as great as the technical challenges.  Renault was used as an illustration being the highest volume single marque manufacturer in Europe (figures for November 2003) and has an estimated $1bn of monthly stock turnover in its supply chain, all in 14V systems.  


The added value proposition for the manufacturer and customer are not always common requirements and 42V does not always offer obvious benefits to the end user.




The 42V system is perceived as much easier to design, electrically, for than 14V system.  This is due to the standardisation effort that has been applied at the early stages of the 42V Powernet development.


The Future


The 42V power network may not gain significant market share, although a predicted peak volume of 10 million vehicles by 2012/13 are relatively good numbers for a few suppliers.  The 42V network may be too late due to the implementation delay over last 4 years and given that other solutions (such as higher voltage soft hybrids) have already made in-road into the market (see graph).




A high voltage power network remains a necessity for future vehicles, but is it too late for 42V?   The main drivers today are environmental legislation and the automotive industry faces major technological challenges.  The higher voltages of existing soft-hybrids may become the de-facto standard power networks in the long-term and 42V may have a shorter life than many existing practitioners realise or will admit.



Predicted future European and North American 

passenger car volumes, listed by primary electrical 

power architecture

(Source: Transparent Engineering).


Martin O'Hara

Telematica Systems Ltd, Trafficmaster UK

22 January 2004


Note: This seminar was a joint meeting of the IMechE Automotive Division, Luton Branch and the IEE Beds & Herts Branch.  Details on other events organised by these learned societies can be found on their respective websites.


Personal Note:


The last items in Peter Hartnetts' presentation  raised many points about the way that the 42V Powernet is moving and whether it has "missed the boat" as far as becoming the next standard power architecture for vehicles to replace the existing 14V network.  Certainly the Japanese with the Honda Insight (144V) and Toyota Prius (202V) soft hybrids have effectively "leapfrogged" the 42V level for much higher voltages to solve the problems of motor assisted drive.  Similarly the Mercedes GST (270V) has gone straight to a higher voltage primary battery.  I attended the first international congress on 42V Powernet in 1999, by the middle of 2000 many semiconductor companies had silicon for these "just around the corner" architectures, 4 years later and there is still no market yet for these products.  Many in the industry blame the recession for the slow down and cancellation of some major 42V system projects, however, there may be more to the lack of acceptance than just the recession.


The MIT Consortium set-up to advance and promote 42V Powernet is a "closed club" and membership is really only open to the larger companies with high R&D budgets as membership alone costs $50,000 per annum.  Consequently the lower tier suppliers (as well as most of the consortium members themselves) have continued developments for 14V systems that have effectively negated some of the technical arguments for adopting the higher voltage network, and at lower cost than a 42V implementation.  The high cost of membership of the MIT 42V Powernet consortium and the clique nature of its operations has undoubtedly put off many lower tier suppliers from doing any development work on 42V.  Coupled with the recession, the initial higher on-cost of 42V systems and the size of the existing supply chain infrastructure as highlighted by Mr Hartnett, I feel the 42V Powernet consortium has unwittingly created the situation where its existence may soon become superfluous to the pursuit of a higher voltage vehicle power network and its valiant efforts on standardisation will all go to waste as OEMs develop proprietary high voltage systems. 



Other Comments: Invited from readers (e-mail to


Comments below were invited by review author and are posted anonymously to protect the respondents;


From: Tier 1 42V Practioner, UK, present at seminar 


The soft hybrids still represent very low volumes and benefit from subsidies, they might represent a promising concept but they are still not a commercial success.  Fuel cell technology might put the 42V technology back on track, as far as I know the working voltage that is most commonly being looked at is 42V.


From: Tier 1 42V Practioner, UK, not present at seminar, comments based on above review 


The MIT Consortium is now dominated by Japanese suppliers rather than the US suppliers that originally formed its core.  The hybrid system developers appear to have taken the lead.


From: IC Supplier, Germany, not present at seminar, comments based on above review 


We developed products for 42V Powernet for 2001/02 but have seen no significant sales volume.  These programmes have been scaled back, although we still have the technology to switch this on if there is sufficient market demand.  There is no new work planned for 42V Powernet this year.


From: Tier 1 ex-42V Practioner, US, not present at seminar, comments based on above review 


The 42V Powernet activity of our company was scaled back in 2001, to such an extent that only 25% of the staffers who worked on 42V are still within the company.  If the technology took off tomorrow we would go from being a lead supplier in 2000/01 to being 2 years behind today.  The loss of 42V Powernet has not effected our profitability, which has improved since 42V spend was halted.


Note: responses have been edited for brevity by the author.

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