Advantages, challenges of vaunted 42-volt systems

Cliff Henke
Posted on November 1, 2001

Already being developed for cars and light trucks, 42-volt electrical systems will soon come to heavier-duty vehicles. They will first migrate to heavy trucks and then reach the passenger market, probably within the next five years, says Halsey King, a maintenance consultant who is also a member of the Society of Automotive Engineers (SAE) Truck and Bus Council’s board of directors. When they arrive, they will dramatically improve bus electrical safety and operating performance, he predicted. However, like all new technologies in the bus market, 42-volt systems will greatly affect maintenance personnel, and the implications for maintenance must be carefully thought through, King added. Starter, alternator to marry
Through years of meetings in various SAE committees, the automotive industry has reached agreement on standards that will triple existing vehicle voltage for both battery output (12 volts to 36 volts) and generator output (14 volts to 42 volts). It’s a move that’s both dramatic and far-reaching, affecting virtually every area of vehicle supply, assembly, component design and manufacture. One such device enabled by the 42-volt system is something called an integrated starter-alternator (ISA). The ISA is basically what it sounds like: a device that performs the functions of starting the engine and generating juice for other onboard systems. The ISA unit is mounted directly on the crankshaft. It functions initially as a starter as the engine is ignited and then automatically switches over to alternator mode. It can support a variety of functions and technologies, including virtual “stop-and-go” power, which are particularly well suited to school bus applications with frequent stops. With the ISA, there is no need to idle the engine. The engine can be shut off each time the vehicle stops and can be started when the vehicle needs to move. That will result in dramatically reduced emissions due to increased engine speed during starting. Other benefits include instantaneous starting, high electrical power to cope with ever-increasing loads from the growing list of onboard equipment, potential improvement in fuel consumption, high efficiency and minimal space requirements. With weight-saving, enhanced vehicle performance, emission reduction and improved fuel consumption, 42-volt electrical systems are the future. Dudley Wass, strategic business unit director for Visteon Corp.’s Electrical Conversion Systems, says that R&D changes will be sweeping. “The move to 42-volt entails a major redesign and re-think by OEMs as it encompasses everything from light bulbs to total integrated systems,” Wass says. Think through maintenance
These profound changes will most certainly affect the shop floor in an equally dramatic way, says King. “Forty-two volt systems will totally rewrite preventive maintenance programs,” he says. “For one thing, it will probably reduce the list of PM procedures to a single sheet of paper - and that list will get shorter and shorter as vehicle systems are revised to take advantage of 42 volts.” All that, he says, is part of a trend that is arguably as long as the evolution of automotive technology itself. On the one hand, new technologies have improved reliability and made mechanics’ lives simpler. On the other hand, they have significantly increased the demand for better-trained mechanics.

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