YOU CAN SEE IT coming. Each year brings new electronic widgets as standard equipment on trucks. At what point does electrical demand for all these added components exceed the truck's ability to power them?
Today's 12-volt systems are keeping up for now, but automotive engineers are convinced that higher voltages will be necessary to power the additional electrical equipment that future vehicles are expected to have. As a result, automotive engineers expect to begin replacing 12-volt systems — the industry standard for more than 50 years — in the near future.
Since the 12-volt system became standard in post-World-War-II vehicles, demands placed on truck electrical systems have increased significantly. Just as the industry gave up on the six-volt standard years ago, engineers are looking to higher voltage systems as the way to quench the growing thirst for power.
If alternators are stressed today, imagine what the load will be like when some of the additional electrical loads that truck engineers envision become reality. With chassis manufacturers under pressure to meet future emissions and fuel economy regulations, one path they expect to take will be to reduce parasitic loads on engines. So instead of belt- or gear-driven accessories, expect to see items such as:
- Electric powered air-conditioning.
- Electric powered water pumps.
- Electronic oil pumps.
- Electric power steering.
- Electronic braking.
With loads such as those, don't expect to see a 12-volt alternator.
Work has progressed to the point that several automobile manufacturers (BMW, Mercedes, and Volvo) will be introducing 42-volt systems in 2003, and Ford is expected to introduce the truck market to the higher-powered system with a 2003/2004 Explorer. The 42-volt Explorer will be a hybrid model combining gasoline and electric power.
“Today's electrical systems are very forgiving,” says one truck engineer. “You twist two wires together, and the light comes on — at least for a while. That won't be the case in three to five years from now when these new electrical systems begin to appear. You will have to know what you are doing.”
Why 42 Volts?
A consortium of auto and truck manufacturers and suppliers (including DaimlerChrysler, Ford, and General Motors) has been at work in recent years working out issues and standards for selecting a higher-powered system.
Selecting a standard voltage is a balancing act. Too small of an increase might mean that the standard would have to be increased again as electrical demands grow. Raising the standard too high could raise fears of safety issues.
According to Underwriter Laboratories, approximately 50 volts is the shock threshold. However, this varies — principally by the surface area of the body in contact with the electrical source and the moisture of the skin (perspiration is more conductive than skin coated with rainwater). A 42-volt standard provides a margin of safety while simultaneously offering a substantial increase in voltage.
The proposed system would charge at 42 volts and operate at 36 volts — three times that found on today's cars and trucks. The advantages that the more powerful system would provide include:
The capacity to power more of today's parasitic engine loads, thereby helping reduce emissions and improve fuel economy.
Improved engine cranking, charging of the electrical system, and more power for future braking, steering, and engine controls.
Smaller wires and wiring harnesses. Tripling the voltage provides the same power at one-third of the current. By reducing the size of conductors, connectors, and other components, weight can be trimmed and costs reduced.
Obstacles to Overcome
But before we can change to 42-volt systems, a lot of obstacles must be overcome to address what are major negatives. For example:
Battery posts must be redesigned. A 42-volt system when disconnected while under load has enough power to generate an arc that melts the battery terminals and scare the absolute fool out of the technician who disconnected the battery cable. In fact, engineers fear that most injuries coming from 42-volt systems will be caused by the instinctive reactions of mechanics jumping away from the electrical sparks, rather than any sensation received by touching a hot circuit.
To address these concerns, the MIT/Industrial consortium formed a standard 42-volt battery committee in October 1999. The design committee is close to reaching an agreement on a common battery connection that will be standard worldwide. To prevent terminal meltdown, the battery would have two primary posts 15 mm wide and 1.7 mm thick. It also would have sensing blades 2.8 mm wide and 0.8 mm thick. The blades would sense battery temperature in addition to automatically turning off power before someone can disconnect a battery cable.
Vehicle incompatibility. The design committee is working on a jump-start terminal inside the engine compartment to minimize the risk of arcing when jump-starting two vehicles with 42-volt systems. The connection may be recessed inside a plastic shroud in an effort to prevent a jumper cable connection between 12-volt and 42-volt vehicles.
New batteries will be required. During the initial rollout of 42-volt systems, trucks will use existing 12-volt batteries wired in series, according to Bob Galyen, director of heavy-duty battery field service for Delphi Automotive Systems. However, he expects that 42-volt batteries will begin appearing within three to eight years.
Electrical system components will need to be redesigned — including wiring harnesses, switches, fuses, relays, solid state components, lighting, and accessories. Even the venerable J-560 connector is getting another look because of the increased voltage. Larry Strawhorn, American Trucking Associations engineer, says that the J-560 must be tightly connected, or it will weld itself together. Higher voltage increases arcing and accelerates corrosion, making it imperative that connectors provide tight contacts.
Effects of higher voltage will be felt throughout the electrical system. For example, fuses will need to be redesigned to accommodate several factors. Because of the arc that 42-volt systems can sustain, it might be possible for poorly designed fuses to have a melted element and still short circuit. Plus, overloaded fuses in a 42-volt system will generate more internal pressure. The plastic body of the fuse must be able to withstand the additional pressure and extinguish the arc.
What does this mean to the truck equipment industry? For all the reasons mentioned above, technicians will require additional training, particularly during the transition from 12-volt systems.
Electrical engineers foresee under-informed technicians creating significant damage — to vehicles and to shop equipment.
According to a recent test conducted by TMC, only 37.6% of technicians knew how to use voltage meters. That statistic may cost shops money given that some of the meters in today's shops cannot be used on 42-volt systems. It also may cause additional damage to customer vehicles when additional voltage is hooked up incorrectly.
Technicians will need to be able to recognize 42-volt systems, whether they are dealing with series or parallel connections, what the voltage should be for a particular circuit. They also should be able to utilize tools properly and follow procedures.
But while training is an issue, a 42-volt system can be good news for the truck equipment industry, especially for power-hungry equipment like cranes, liftgates, and ambulances.
Liftmoore Inc of Houston, Texas, already is using 24 volts to power its 6,000-lb electric crane. The company's largest model requires a specialized charger and two 12-volt batteries connected in series. Increasing the voltage of truck electrical systems in effect would create “plug and play” installation for even the most power hungry models.
“A 42-volt system would be a huge advantage for us,” says Herb Koenig, president.
Trailer manufacturers and customers, having recently gone through their own power struggle involving the use of the J-560 connector to illuminate the in-cab ABS warning lamp, are not as enthused. At a recent industry meeting, some fleet operators said the higher voltage will lead to higher frustration levels. They are particularly concerned about the transition period when the industry begins switching from a 12-volt to a 42-volt system.
One major area of concern: compatibility between tractors and trailers with different voltage systems.
“It's one thing to have a 42-volt system on a straight truck where only one electrical system is involved,” one fleet manager said. “But connecting the electrical systems of tractors and trailers will be a disaster. I'm glad we won't see this before I retire!”