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Modern Trucking Techniques
The promise of the 42-volt electrical system
We’ve reached the limit of what can be done with 12-volt systems, so what’s next?

by Paul Abelson, technical editor

About two years ago, the hottest topic among both automotive and truck engineers, even hotter than the 10/02 EGR engines, was 42-volt electrical systems.

By increasing electrical force, more work could be done and other advantages could be realized. The 42-v electrical systems were due to be phased in on several makes of American, Japanese and European cars and trucks in 2004.

The promise of 42 v goes beyond making electrical systems function better. By redesigning systems to take advantage of the higher voltage, fuel economy can be improved, weight can be saved, idling can be reduced and truck engineers will be free of many compromises that have influenced and restrained truck design.

Currently, all accessories, subsystems and components that must be driven are located at or near the front of the engine. They get their power through belts or gears driven off the front of the crankshaft. These include the alternator, air conditioner, power steering pump, air compressor, water pump and radiator fan. Each of these is sized as much because of its location as for the work it has to do. Because we have come to the limit of what can be done with 12-v systems, we must drive these devices mechanically.

But think of what can be done if there were enough electric power. Here’s how our trucks would change:

  • n Driven by computer-controlled electric power, air conditioners, water pumps, air compressors and radiator fans will operate at their most efficient speeds for their load conditions regardless of engine rpm.
  • n Power steering pumps, a continual power drain now, will be eliminated, replaced by electric steering.
  • n Alternators will be combined with starters within the flywheel. Depending on current flow controlled by a computerized gatekeeper, the Integrated Starter/Alternator/Damper (ISAD) will start the engine, generate electrical current and even dampen engine vibrations to keep them out of the drive train.
  • n Free from the need to be at the front of the engine, air-conditioner compressors will be located closer to or inside truck cabs. Water pumps can be integrated with radiators. Air compressors can be mounted close to air tanks and brake chambers.
  • n Without the constraints of locating accessories and the compromises forced by engine speed, truck designers/engineers can develop newer, more aerodynamic and efficient shapes for truck cabs.

The question I put before some of our industry’s leading electrical engineers was, “How soon will we have 42-v systems?”

Brian Lawrence of Xantrex thinks “the momentum has died.” Truck builders and component suppliers are still working on 42 v, but European-style 24-v systems may offer the benefits of higher voltage without major costs for research and development. With the economy as it is, the limited funds available must be applied to projects with a more immediate return. Several truck builders have European ties (Freightliner, Sterling, Western Star, Volvo and Mack). It would be easy to adapt technology from their parent companies and use 24-v systems.

Truck-Lite’s Brad Van Riper also feels “the momentum for 42 v is starting to die.”

While higher voltage makes possible such advances as steer-by-wire and variable engine valve timing, it puts additional strain on many subsystems such as lighting. Truck-Lite currently produces 10- to 30-v lighting for the Armed Forces, who use the worldwide 24-v standard for trucks. As soon as there is a demand, Truck-Lite is ready to launch its OmniVolt products, capable of handling up to 48 volts. But Van Riper thinks there is now more pressure to globalize, to harmonize standards worldwide, than there is to develop a new system.

“With 24 v, trucks can have dual systems; a 12-v bus for lighting and radios, and a 24-v bus for starting and the systems currently driven mechanically,” Van Riper said.

Charlie Groeller of Mack agrees that the hype about 42 v has gone, but there is still interest. He should know. He chairs the Electrical Subcommittee of the SAE Truck and Bus Group. His organization will approve any new electrical systems engineering standards for the next generations of trucks.

“At Mack,” Groeller said, “we probably won’t do anything until our next platform comes out ... probably in the 2008 to 2010 time frame, not before. There’s a need, but technology must catch up.”

One major concern is arcing. When you break a 12-v, or even a 24-v circuit, arcing is not a problem, but with 36 v (42-v circuit with the alternator not charging), current will arc between connectors.

As Charlie said, “We’ll need different relays and circuit protectors. Connectors will have to be redesigned. Arc suppression must be integrated. And technicians will need training on how to avoid problems. If 12-v connectors are used in 42-v circuits, they’ll work until the first time they’re disconnected. Then arcing may damage the old style 12-v connectors. The same holds for fuses and circuit breakers.”

Carl Smith of Sure Power Industries feels there is a future for 42-v systems, but he mentioned that “at present, all experimentation with 42 v is on cars. The prime motivator is emissions control, especially shutting the engine down when not moving and starting it with the accelerator. We still don’t know if that will be possible with 80,000-pound trucks.”

New technologies being developed include true electric braking, Carl said.

“Dynamic electric braking has each wheel turning a motor/generator that generates current to charge batteries and super capacitors. When these devices are full,” Carl told me, “a resister bank will convert the current to heat.”

This would be an ideal auxiliary braking system because it captures kinetic energy for future use. Current can also be reversed on the regenerative braking system, to put extra power to the wheels for hill climbing and bursts of acceleration.

Other voltage systems may leapfrog 42 v. Hybrid cars and SUVs are operating at anywhere from 140 v to 300 v, and Caterpillar’s MorElectric Truck uses 340 volts. Any switch from either 12 v or 24 v will, according to Mack’s Groeller, “cost billions of dollars in just tooling costs worldwide.” There have been DC to DC converters and developmental 42-v vehicles made, “but no one has yet mass-produced 42-v components.”

Caterpillar plans to launch to MorElectric Truck sometime next year. The Caterpillar system, by the way, does not require a Caterpillar engine. It will work with any engine, but the truck architecture must be modified.

If successful, it may eliminate the need for 42 v altogether and take the industry to a higher level.

Why do we need higher voltage?
Higher voltage helps electricity work more efficiently.

A good analogy is torque applied by a wrench to a fastener. You can apply 500 lbs.-ft. to a wheel nut by using a 2-foot-long wrench with 250 pounds of force, a 4-foot wrench with 125 pounds, or a 5-foot wrench with only 100 pounds. If it were practical to use a 10-foot wrench, you’d need only 50 pounds. The math works out the same, but the longer the wrench, the less force is needed to achieve the desired result.

The same applies to electricity. Work is measured in watts (w), the product of electrical force, measured in volts (v) times the amount of current, amperes (amps).

Watts = Amps X Volts

The higher the voltage, the less current is required. By doubling or tripling voltage, amp draw can be cut by half or two-thirds for the same amount of work. For a given level of amps, increasing volts allows the system to do more work.

Amperage is what heats wires, requiring larger, heavier, more expensive wiring as amp load increases. With higher voltage, wiring can be kept smaller while work increases.

But the most important consideration is that, just as a longer wrench lets you get work done with less effort, higher voltage lets the truck’s system get its work done using less current.