The decision that needs to be made before the industry can progress further is how to address the need for more electrical power on-board the automobile. A number of groups such as the MIT Consortium, Forum Bordnetz, and SAE have agreed that 42 volts is a reasonable choice for the voltage of a new automotive electrical system. However, after picking the voltage level, the real choices have to be made.

There are three important aspects of an automotive electrical system - the generation, storage, and distribution of the appropriate power levels.

In the mid 50s the industry also needed more electrical power because of the higher displacement engines that required additional ignition energy. The switch from 7 V to 14 V was accomplished in two years. The proposed switch from 14 V to 42 V is slightly more complicated.

Various architectures have been proposed for the introduction of the 42 V electrical system:

• Single 42 V architecture - This would consist of a 42 V alternator, 36 V starter, 36 V battery, and 36 V bus. This would be the easiest to do on paper but the most difficult to pull off. This single volt scenario would also be the most expensive since all the electrical components in the vehicle would have to be redesigned to operate on 42 V.
• Dual voltage architecture - Under this scenario, both a 42 V and 14 V bus would be available. This is where the decisions need to be made so that the industry can move into the 42 V electrical system. First of all, there is a choice of having two alternators, one 42 V and one 14 V. If the choice is made to use a single 42 V alternator, then another decision is to whether or not to have both a 12 V and 36 V battery on board.

A 42 V integrated starter alternator is used to generate 42 V. A 36 V battery is used along with a 12 V battery. Two bi-directional dc-to-dc converters are used to give an almost redundant supply of both 14 and 42 volts.

The system also uses a 42 V integrated starter alternator along with a 36 V battery. Two dc-to-dc converters supply various voltages to components as needed. Under this scenario, a pulse width modulator (PWM) is used to chop the 42 V such that 12 V components such as lamps can be used on a 42 V system.

There are also a number of variations on the dual voltage system. Both of these are variations where two batteries are used. They differ in how some 14 V components get their energy - either with a PWM and/or dc-to-dc converters.

According to Ted Vartabedian, Systems Engineer, Body Electronics, Siemens Automotive, different scenarios may be used for different car lines. It may take two decades for all vehicles to be on the single 42 V electrical system. Of course, all these statistics are subject to change depending on advances in technology and customer acceptance.

The present day challenge is for the automakers to decide what architecture will be used and when. In any case, the suppliers and automakers must deal with the challenges involved in the generation, storage, and distribution of the 42 V.

• Generation - A number of suppliers are working on methods to generate the 42 volts. Present day Lundell alternators can produce about 2 kW of power, which is not enough power. Upgraded belt-driven alternators being examined by Delphi can produce 3.5 kW. Moreover, based on the Lundell design, 6 kW appears to be the maximum output available. A number of companies including Bosch, Delphi, Mannesmann Sachs, Siemens, and Visteon are developing integrated starter alternators (ISA) that may be capable of producing the required 10 kW of electrical power. The ISA can be mounted on either end of the engine's crankshaft. Most of the prototypes are being mounted on the transmission side of the engine, replacing the flywheel. The big plus for the ISA is the fact that the vehicle can be operated in a start/stop manner to conserve fuel and reduce emissions. Norman L. Traub, Technology Integration Manager, Delphi Automotive Systems points out with the capability of an ISA, the industry is beginning a 20 year technology revolution that will change the cars we drive. An ISA can produce enough power to allow a number of new technologies to be added to the vehicle.
• Storage - Some type of storage device must be developed to start the vehicle. Jim Gracyalny, Sales Director, Inspira, Johnson Controls believes that the spiral wound technology using absorbent glass mat (AGM) is a very good choice for the 36 V battery. Johnson Controls has just acquired Optima Battery that has been producing spiral wound batteries for some time. There are a number of variations in the spiral wound technology; one is where lead in the form of thin metal film is used in place of flat sheets of lead. Other batteries using technologies such as Lithium Ion and Nickel Metal Hydride are also under consideration.

  A key challenge for the battery is to be able to store energy especially if the ISA is used for regenerative braking. Ultra- or super-capacitors are also being considered for use together with a 36 V battery to supply the quick power to accelerate an ISA vehicle that is in the stop mode at a stop light or in traffic. To size the battery properly more details about the 42 V electrical system need to be decided so a final design can be developed.

• Distribution - Once the source of the 42 V and a method to store the energy have been determined, the energy must be distributed throughout the vehicle. Under a dual voltage architecture, many of the electrical components that operate on the 14 V bus will not need to be redesigned. However, control electronics will need to be developed along with items such as fuses, switches, and relays. One of the big winners in moving to 42 V will be the semiconductor industry. According to Jeffrey Sherman, Strategic Marketing Manager, Infineon Technologies Corp., semiconductors are available that will work on a 42 V electrical system and because of the new voltage it is possible to continue to make them more cost effective. Prices of semiconductors have been decreasing and their uses in automobiles have been increasing. The cost of semiconductors in a present day vehicle is about $230.

A concern under the 42 V system is arcing when removing or replacing fuses or when contacts in relays and switches open and close. Michael E. Williams, Sales Manager, Pudenz has stated that the company has developed a 42 V fuse that uses tin-plated copper terminals instead of zinc. Copper is less susceptible to arcing than zinc. Also, Pudenz is developing a footprint that will allow only a 42 V fuse to be inserted into a 42 V electrical circuit. According to Jerry Bricker, General Sales Manager of Omron Automotive Electronics, Inc., there is the possibility of arcing in present-day technology relays and switches but the company has been developing new technologies which will work under the 42 V system. However, under a dual voltage architecture, many of the circuits will remain on the 14 V bus and thus many of the present day relays and switches will continue to be used.

The introduction of the 42 V electrical system will also bring about the use of more multiplexing. Depending on the electrical system architecture chosen, the look of the system may differ. Under this scenario, a CAN bus is used to communicate among a series of network boxes located strategically throughout the vehicle. This will help reduce the complexity of the wiring harness with proper power distribution control electronics.