To meet ever increasing electrical power demands, automakers are moving to increase vehicle battery voltage from today's 14V to approximately 42V. It has been more than 40 years since US carmakers switched from the standard 6V system, a change triggered by similar power considerations. During that time, vehicle electrical power consumption has increased by more than 50 percent. Every year, new features and functions are added; the more recent ones include cell phones, personal computers, and satellite navigation systems. Currently, less than 30 percent of the energy in gasoline is used for locomotion; the remainder is wasted by inefficient components and burned off as waste heat during engine idling.
The next generation of automobiles will have even more electronics and require a power source with an output of more than three kilowatts, the limit of today's 14V system. A 42V system will deliver around eight kilowatts and allow better management of the higher power requirements. Numerous other advantages include:
- Reduced electrical current levels
- Downsized wiring and electrical components
- Lower electrical system cost
- Reduced mass and volume
- Improved fuel efficiency
- Lower vehicle noise, vibration, and harshness
- Improved system stability
A 42V system also sets the stage for advanced technologies that will allow a switch from mechanical belt-driven systems to those that are electrically powered. Possibilities include electric power steering, electromechanical brakes, electrical HVAC systems, electromagnetic valve trains, integrated starter-generators, and electronic ride control systems. The so-called "beltless engine" of the future will be another reason for lower weight packaging (because accessories can be located outside the engine compartment), leading to higher efficiency that improves gas mileage and reduces emissions.
Initially, cars are expected to have a dual 14/42V system, which will help manage costs by avoiding a simultaneous switch of all vehicle systems to the new 42V standard. During the gradual changeover, some components will operate at 14V and some at 42V. This could persist for a few years, given that some 14V components, such as lamp filaments, are more rugged and last longer than their 42V counterparts. It could be that certain components, such as sensors, spark plugs, radios, and other electronic devices will always work better at 14V than at 42V.
Toyota Motor has already begun selling a 42V luxury sedan, but only in Japan. A few European cars have two lead-acid batteries on board, so higher voltage electrical system should follow soon. About two dozen vehicles with various types of 42V systems are in advanced design stages. US consumers will probably see the first dual 14/42V vehicles on showroom floors beginning with the 2004 model year, when General Motors rolls out its first-generation 42V system in a hybrid gas-electric pickup truck. Volume ramp-up is expected to start with the 2007 model year, particularly in large and midrange automobiles and light trucks (especially SUVs), where power-hungry features, fuel consumption, and emissions are becoming major issues. At least one forecast places production of 42V vehicles at around 13 million units by 2010.
Before 42V systems can be adopted widely, many engineering problems must be addressed, including the engine/electrical system architecture and a migration strategy (dual 14/42V systems vs. straight 42V systems). Short-term challenges associated with dual voltage systems include more wiring, extra weight, and added complexity. Regardless of migration path, suppliers need time to develop new components and a part identification system that distinguishes between 14V and 42V parts.
Evaluation of Electrical and Electronic Components. While 42V is not far from 14V in physical terms, real-world issues are a cause for concern. Current 14V designs won't automatically work at 42V; even simple fuses will not migrate, let alone dimmers and active load controllers. Some fuse panel and harness makers have found that common 14V mini- and maxi-fuses do not behave properly at 42V. They can fail to interrupt excessive currents properly, causing serious overload conditions. Also, interconnection technologies have evolved for optimal cost and performance in a 14V environment. The present design of connectors, circuit breakers, and relay contacts may not be optimal at 42V. Therefore, manufacturers must re-evaluate component suitability for the higher voltage. Tests can range from simple continuity tests to full electrical characterization of a component's functional performance at 42V.
Reliability Issues. At 42V and higher power levels, many components, such as wires and relays, experience electrical stress that is three times higher than before. With higher stress, components tend to break down more often. Therefore, component and module manufacturers have to perform more reliability testing, such as burn-in and accelerated stress tests, to ensure adequate service life.
Safety Issues. Safe distribution of 42V power throughout a heavily optioned automobile also is a challenge. In the first place, the 42V standard was established because higher voltages create human safety issues. For example, 50V can stop a human heart, and anything higher than 60V requires more heavily insulated wires and connectors, which add weight. To prevent fires, electrical distribution designs must allow for jump-starting at the higher voltage, and provide protection if battery connections are reversed.
Component and Conductor Arcing. Relay, switch, and conductor arcing is another problem that must be addressed; its potential for serious damage is greatly increased in 42V systems. Recent research shows that 42V arc energy is 50 to 100 times higher than in a 14V system. Such arcing can generate temperatures up to 1800F, ignite fuel vapors, start a fire in plastic insulation, and even melt metal. Simply redesigning relays, switches, and fuses for higher voltage and using flame-retardant materials is not a total solution; these component designs should suppress arcs. The same is true for other connections, particularly those that could be opened during replacement of fuses, batteries, and other components. Mechanical design features must ensure that electrical terminals are correctly seated and locked; therefore, increased use of clips, clamps, and shields may be required.