January 2002. In an update of his recent November feature article, Mike explains why 42-volt electrical systems are even further into the future than originally thought.

In a feature article this past November, I talked about the challenges facing carmakers on the implementation of 42-volt electrical systems. Such systems had been thought to be coming in the very near future. However, in recent months, there have been several announced delays or outright cancellations of programs featuring this new technology. For example, 42-volt technology was a big part of Ford's promise to improve the fuel economy of its SUVs by 25%. Now it's been announced that Ford's 2004 Explorer will not be built with an integrated starter/alternator after all.

The technician's group iATN recently held a conference in Dearborn, Michigan. One of the speakers was Paul Nicastri of the Ford's Research Laboratory. At the conference, Nicastri dug into the details of the technical issues behind the slowdown. It looks like some of the technology is just not ready and some of the expected benefits haven't proven out. Another major factor in the delay has to do with the slowing economy and funding problems.

One area of technology that doesn't seem to be ready yet are the wire harness and connectors. It turns out that the energy in an arc is much higher in a 42-volt system than in the current 12-volt system. This impacts the design of fuses, switches, relays, motors and especially 
connectors. The problem is not when the connectors are mated, but when they're pulled apart. Just like in the old days of points and condensers, when the contacts are opened, the current continues to flow through the gap because of the arc that's formed. Temperatures in that arc can reach 6000¡C with a 42-volt system!

Nicastri showed a short video clip to illustrate in practical terms what this really means. A mating pair of terminals were hooked up in a 17-amp circuit with a resistive load. With the current flowing, the two terminals were pulled apart. A bright, burning arc appeared, then a flash occurred. When the parts were examined afterward, the two terminals were burnt so badly they couldn't be reassembled. The male terminal's tip was burned right off.

There are solutions for this, Nicastri emphasized. One is to design the electrical and wire harness systems in such a way that it's impossible to disconnect terminals when there's power in the circuit. Where this can't be done, as in the case of relay contacts, the terminals will have to be built heavier, spaced farther apart and perhaps protected by arc-suppression devices. The shape and material of the terminals and contacts may also have to be changed. This, of course, will cost both money and time.

Another area of great concern are the battery connections. Seven automotive companies have been working with the Massachusetts Institute of Technology to come up with a new way of connecting to the battery. The new system must make it impossible to mate or unmate the connections while there's a heavy load in the system. Arcing at the battery posts in a system with this much energy could create a major hazard, as well as damage to the system components.

In today's automotive systems, electronic modules and the like are designed to be somewhat tolerant of momentarily reversed battery cables; the system will withstand some of it. This is not true with a 42-volt system. The silicon content of the electronics will not be protected against reverse voltage. The specification calls for no more than Ð2 volts for a maximum of 100 milliseconds. For this reason, new battery terminals will be designed to make a reverse-polarity connection impossible. They'll also be designed so there'll be no easy access to the alligator-style jumper cables we're all so familiar with.

A design proposed by Delphi looks pretty much like a standard battery, except there are no side-mount terminals for the cables. Instead, on top of the battery, pointing to one side, are two dual-terminal connections. 
On one side, there's a long blade and one shorter blade in each of the two-connector bodies. When you pull the harness connector off, the short-blade side opens first, with that blade connected to a power relay. 
Opening up the short-blade side opens the relay and cuts the power to the long-blade side. This effectively makes it impossible to disconnect the battery with the power on or to hook jumper cables to the higher voltage battery.

Of course, this is Delphi's proposal. It hasn't yet been settled on whose proposal will eventually become the industry standard. Until these decisions are made, development of the 42-volt electrical system will continue to be delayed.

As you can imagine, when 42-volt systems do start to appear, only small numbers of such vehicles will be on the road. To enable them to be jump-started will require the development of some technology that allows a 12-volt system to jump the 42-volt system. This can be done with a DC-to-DC converter. Such a device is similar to the inverters seen in travel trailers. The electronics chops up the 12 volts into pulsating DC, runs it through a transformer to step up the voltage, then rectifies it back into DC at the 42-volt level. But not only does this add yet another electronic module, it also doesn't work as well because the jump-start 
in this case is being used to charge a dead battery, not to run a starter motor. Estimates of up to five minutes in moderate weather, longer in cold weather, are being bandied about.

There are yet other issues to be addressed in terms of the wiring harness. Nicastri showed the results of an experiment that had been done regarding corrosion resistance. A pair of 20 AWG wires were laid side by side. Both pieces had a section of insulation about 5mm wide removed. The two bare spots were separated so there was 6mm of insulated wire, top and bottom, separating them. The first time they did this there was a difference of 12 volts between the wires as they dripped salt water on the two wires. After six hours of this, the wires showed slightly green corrosion. Nothing to worry about.

When they repeated the same test with 42 volts between the wires, the results were dramatically different. Within 20 minutes, one of the wires rotted off. The fact is that the higher system voltage is going to make it necessary for designers to do a much better job of protecting wire harness connections from salt and other corrosive elements. A viable 42-volt system can't be considered ready to go until this is done.

Susceptibility to Fires
It's now been almost 50 years since the wide-scale introduction of 12-volt electrical systems. Still, every year, there are thousands of fires in vehicles that result from faults in their wiring. Well, 42-volt systems may be even more sensitive to this. For example, if the wire insulation in a 42-volt system is chafed or damaged, say, from rubbing on a sharp edge of metal, there could be quick, momentary arcs from the wire to ground. This short-duration arcing may not generate enough heat in the fuse to cause it to blow. At the same time, as mentioned earlier, there's a lot more electrical energy or heat in a 42-volt arc. This increased potential for fire may require the use of either more heavily insulated wires or electronic arc-detection circuitry.

A new set of fuses have been developed for 42-volt systems. Such a fuse fits in the same place as the fuses used in a 12-volt system. However, the system is designed so that a common 12-volt fuse cannot accidentally be put into a 42-volt-system vehicle.

There's also the issue of unmet expectations. For instance, the current average life in Michigan for a 12-volt battery is four to five years, with seven to eight years possible if the driver doesn't mind a jump-start now and then. So far, the demonstrated life of the 36-volt battery needed for a 42-volt system has been approximately three years. Because of this, many of the prototype vehicles I've seen displayed have had three regular-size car batteries in them. Because increased weight and fuel economy move in opposite directions, you can imagine that no one likes this option.

So far, the demonstrated fuel economy improvement of a 42-volt system has been on the order of 5%. While that's not bad, it's not nearly the 15% that had been hoped for. The engine stop at idle with instant restart feature of an ISAD makes a 42-volt system very appealing, especially in an EPA city drive cycle. Problem is, the increase in weight due to the ISAD, plus the extra batteries required, offset most of the weight savings that result from using lighter wiring harnesses.

Without a doubt, though, the major obstacle to adopting a 42-volt system is cost. A 1kW DC-to-DC converter is about a $200 ticket at today's prices. Even long-term, this is a $100-per-vehicle addition.
"We sell the cars and we give away the electrical system," Nicastri said. "No one is going to go into a dealership and ask to buy a new car because it has a 42-volt electrical system." This means that the carmakers are going to be holding the bag on any new costs associated with the system. Until the new parts can be tooled and brought to high production levels, the costs will be higher.

If all this sounds like gloom and doom, it shouldn't. Nicastri made it very clear that 42-volt systems will come, and for a very good reason-they have to. Unless someone decides to change the list of coming features, 2010-model vehicles will not have a serpentine drive belt; all those loads will be handled electrically. With the addition of electromechanical valvetrains, heated seats and heated catalytic converters, today's 
12-volt system just can't possibly do it all.

The good news is that the automakers are doing their homework on 42-volt systems. They're discovering the differences, finding the challenges and developing the needed solutions. This may take a while, but it's better to take the time and get it right.