42-Volt Challenges: Arcs and Sparks By Tim Moran Automotive News The auto industry was lucky the last time it boosted voltage in car electrical systems. That was in the late 1950s, when the challenge of starting large, high- compression engines led engineers to push from existing 6-volt technology to the 14-volt charging system and 12- volt battery. Unknowingly, the industry dodged a bullet in making the switch. Current flow below 15 volts is just under the threshold for persistent arc discharge. Sparking between electrical contacts occurs ina 14/12-volt system, but the arcing is unstable and is broken easily. Boost the voltage to the emerging standard of 42 volts for charging (with a 36-volt battery), though, and what you get is an effect like a series of small welder’s arcs. The effect between connectors can generate temperatures above 1,832 degrees F. Connectors that vibrate loose can create the effect; so cana car owner accidentally disconnecting alive wire or a faulty switch. The size of the connector doesn’t matter. What matter are the space be- tween charged surfaces and how the contacts pull apart. Almost all switches experience a small bounce as they bring electrical contacts together, and the result is like acar constantly trying to strike its own match. It is one of the biggest chal- lenges to the higher voltage car. Need for new connectors? “The auto industry is going to have to face up to this,” said Thomas Keim, at the SAE World Congress the first week of March. Keim is director of the Massachusetts Institute of Technol- ogy consortium, a global leader in set- ting 42-volt standards. Keim said aviation has dealt with this kind of arcing for years, and only strin- gent, intensive maintenance has helped prevent electrical fires. Most vehicles don’t receive that kind of maintenance, and mechanics agree that car wiring harness problems are notoriously dif- ficult to repair. It may take a new connector sys- tem in the car to handle electricity safely, at least on the high-power cir- cuits that drive 42-volt features. Researchers from the Fujikura Ltd. Automotive Products Division in Ja- pan have posed a partial solution. Fujikura’s Koji Sakiyama said re- searchers installed permanent magnets in either side of a 42-volt plastic wir- ing harness connector. The magnets create a field that electrical arcs must go around, making them longer and easier to break off, within 40 to 80 mil- liseconds. Sakiyama urged develop- ment of a global standard for safe dis- connects. Challenge for switch makers Switch makers, meanwhile, are fac- ing many instrument panel challenges that change the way electricity flows. At lower voltages, switches often carry the actual current used to drive devices in the car. Higher voltage switching will rely instead on indirect, low-voltage controls that may actuate remote power-handling solenoids, similar to that ofa car’s current ignition switch. Suppliers also are reinventing the au- tomotive fuse box, introducing smart fuses and computer-controlled switches to handle the loads imposed by 42 volts. The simple replacement cartridge fuse likely will be a thing of the past for high-voltage electronics. MARCH, 2001 Reprinted with permission of Au- tomotive News. Flick of the switch The advent of 42-volt power systems will prompt suppliers to redesign switches to: ¢ Generate temperatures to 1,832 de- grees Fahrenheit ¢ Melt metal or burn plastic «Ignite fuel vapors Page 1 of 1