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The Transition to 42-Volt Batteries and Its Impact on In-House Fleet Maintenance

March 2004, by Mike Antich - Also by this author

The 12-volt battery, along with the automotive electrical system it supports, will more than triple its voltage to 42 volts in the next four years. The three forces driving a new, higher voltage standard for automotive electrical systems are:

1. The increased power demands from convenience/comfort features and new electronic/telematic devices.

2. Mandated emission standards.

3. Mandated fuel economy standards.

Vehicle electrical demand has doubled in the past 20 years and the current 12-V system is taxed to provide this increased power.

Second, emissions regulations are adding impetus to adopt a 42-volt system because it allows automakers to significantly reduce hydrocarbon emissions by enhancing engine efficiency.

Finally, a 42-volt architecture can increase fuel economy by 10 percent or more because the more powerful electrical system allows the replacement of comparatively inefficient components driven by belts connected to the engine, which drain power and consume fuel. In the near future, 42-volt systems will enable the introduction of steer-by-wire and brake-by-wire systems, eliminating most hydraulic and mechanical systems in automobiles and replacing them with electronic components that do not draw power from the engine. A 42-V system makes “idle stop” possible, which reduces tailpipe emissions and increases fuel economy. Less than 30 percent of the energy in gasoline actually moves a vehicle; the rest is wasted heat burned off during idling or squandered by inefficient components. If a vehicle had a starter motor powerful enough to provide “instant start” at the tap of the gas pedal, then it could shut off the engine while waiting at traffic lights or coasting. This eliminates wasteful idling, saving gas and reducing emissions.

General Motors has introduced a “flex power” hybrid propulsion system in certain models of its 2004 Chevy Silverado and GMC Sierra, which provides 10-15-percent better fuel economy. When the truck is coasting or idling, the gasoline engine shuts off and is restarted by drawing power from a 42-volt lead-acid battery. Another benefit of 42-volt architecture is electronically controlled valves. By electronically actuating the valves, a microprocessor can vary the valve timing to allow the engine to produce more power relative to its size, while, at the same time, reducing emissions. Another way a 42-V system can reduce emissions is by pre-heating the catalytic converter. A cold catalytic converter is inefficient at startup, which is why vehicles emit the most emissions before warm-up. A 42-V system can pre-heat the catalytic converter so that it is operating at optimum efficiency shortly after turning on the ignition.

6-V to 12-V Deja Vu

Frost & Sullivan predicts that in 2008, approximately 5 percent of vehicles will use 42-V technology. By 2012, up to 20 percent are expected to feature 42-V systems, increasing to 40 percent by 2015. Some industry analysts predict that all new vehicles will have 42-V systems by 2020. Today’s situation is comparable to 50 years ago when automakers switched from the 6-V to the 12-V battery. GM started the switch in 1955 and VW was the last to adopt it in 1966. It took 11 years to make the transition. The changeover to 42-V will most likely be deployed first in high-series cars moving gradually to less expensive vehicles. Automakers probably will not replace the entire electrical system all at once; the old 12-V system will still power windshield wipers, radio, and headlights, while the new, higher-voltage system will power brake-by-wire systems or electronically actuated engine valves. Some vehicles will probably have dual batteries, or a 12-volt step-down, for certain legacy 12-volt components.

Fleet Maintenance Issues

Why was a 42-volt standard selected? Why not a 100-volt standard, for instance? The reason is safety. At a 42-V level, an electric shock is not life threatening if the battery’s positive terminal and the vehicle frame are touched simultaneously. But there are safety issues related to a 42-V system such as arcing. A frayed wire in an automotive electrical system can cause arcing, lightning-like leaps of electricity through the air. Arcing in a 42-V system is 50 to 100 times higher than in a 12-V system, raising the potential risk of burns to mechanics. Other issues are battery lifecycle and expense. Currently, 42-V batteries do not have the same long-life characteristics as their 12-V counterparts, and they are more expensive to replace. In terms of in-house fleet maintenance departments, new training will be required along with the expense of acquiring new tools and diagnostic systems to deal with 42-V system service issues. One thing is certain. During this decade, fleet maintenance will become more complex and require even greater levels of expertise on the part of your in-house technicians.

Let me know what you think.

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