Electrical systems have become a focus for OEMs as well as truck drivers. Why? As electrical loads increase, systems have not kept up - and that can lead to premature failure. In the heavy trucking industry, most batteries don't last one year, and most alternators don't make it past two years of life.

According to Brian Lawrence, heavy-duty truck manager for Xantrex Technology, the primary culprit for early death is over-discharge of the vehicle's batteries which makes alternators work harder. "What's caused much of the problem is the exploding growth of inexpensive consumer-grade inverters, which convert DC power to AC for onboard electronics," he emphasizes. "They've added additional voltage draw on batteries and have encouraged poor battery care.

"Today, a truck is much more than cab and trailer," he says. "It is a home away from home for drivers who have brought the comforts of home with them on the road. When they do, it can spell trouble." For example, many drivers will use DC refrigerators and low-quality inverters to run various AC devices. This combination can draw down batteries to levels that can ruin their ability to accept a charge.

"The reason is that low-grade inverters offer little - if any - protection from drawing a battery too low to recharge," Lawrence explains. "The adage 'you get what you pay for' is especially true with inverters. The cheaper they are, the less protection you have. Without adequate 'shut-off protection' - which cheap systems don't have - a frenzied alternator will eventually burn itself out trying to recharge truck batteries."

Lawrence says the scenario doesn't get much better when you're idling at a truck stop. "You might think you can run all your 'goodies' with no impact on your batteries, but often that's not the case," he says. "An alternator charges far less at idle than when on the road. Electrical loads can easily exceed an alternator's ability to recharge. If a truck idles frequently and battery levels are drawn down to handle these DC loads, there are four significant consequences: fuel is wasted, the environment is polluted by exhaust, alternator life is shortened and again, the charging ability of batteries can be seriously compromised. At Xantrex, we are finding that truck drivers expend batteries three- to four-times faster than necessary, and burn through twice as many alternators as they should."

For an average truck, all this equates to premature failures that can cost hundreds, if not thousands of dollars in parts replacements. But, more important, says Lawrence, it can mean lost productivity and missed deliveries. "And missed deliveries are the true cost," he says. "Ever have an alternator go out in the middle of the night and have to find a dealership to do a repair? In these days of tight belts and even tighter margins, I suspect that very few people in the trucking industry are prepared to write off this unnecessary expense, or chance downtime."

Why Batteries Die
The field experience of Xantrex engineers - along with input from major battery manufactures and industry experts - suggests that there are three major contributors to poor battery life in heavy trucks:

* Over-Discharge: Deep discharge does irreversible damage to engine starting batteries on a fundamental physical/chemical level. Each discharge below 50 percent capacity negatively impacts longevity. Each discharge below 75 percent discharge is so harmful that just a handful of such events can end the useful life of a battery.

* Cycling: Routine cycling, even as modest as 25 to 30 percent depth of discharge, is known to have a negative affect on batteries.

* Battery Charging Profiles: Battery manufacturers suggest the best charging profiles for long-term battery care in cycling applications involve multiple stages - typically, a constant current stage followed by a constant voltage stage and then maintained with a 'float' voltage stage. Ideally, voltage levels should be adjusted based on battery temperature. Truck charging systems typically rely on single-stage charging, which traditionally, has been adequate for starting systems. However, this is not adequate for heavily discharged batteries.

Increasing the Life of Batteries
Any solutions for increased battery life? "There are," Lawrence says. "Although it is very difficult to achieve a meaningful field test with controlled variables, there is mounting evidence that vehicles employing a managed electrical system can experience better battery life and lower associated costs than those offering traditional DC systems. This managed system includes an AC infrastructure (otherwise known as shore power, using an outside power source for high-draw items, such as microwaves, heating and air conditioning), and industrial-grade inverters or inverter/chargers. Industrial grade inverter/chargers are the ones offered by most of the truck OEMs."

According to Lawrence, AC power takes a "systems" approach to cab convenience power, the specific technical features of most good quality inverters and inverter/chargers plus the use of shore power when available. "The AC system actually uses driver behavior, which today is battery unfriendly, to extend battery life - and save truck operators money."


Here's why Lawrence feels this combination is good for trucks:
* "Smart" Over-Discharge Protection (Low Voltage Disconnect): The best inverter/chargers have sophisticated over-discharge protection. The combination of several "smart" algorithms detect dangerously low discharge levels and shut down AC output, preventing further discharge. In addition to eliminating the need for dead-battery jump starts, this feature is sophisticated enough to avoid nuisance shut downs when load conditions create temporary low voltage excursions.

* AC Plug-Ins: If you order a truck with AC infrastructure, or have it installed on the aftermarket, AC wall outlets can become a self-fulfilling prophecy. As soon as they are present, a driver's natural preference for better performing - and less costly - AC appliances and equipment will shift most "house" loads to the AC system. Once on the AC side, the battery is protected from over-discharge by the inverter/charger's low- voltage disconnect. According to Lawrence, some fleets prefer to switch even common DC loads, such as refrigerators, to AC for this reason.

"What's more, AC infrastructure incorporates built-in features to capitalize on the availability of shore power," stresses Lawrence. "Originally offered as a necessity for block-heater connections in cold areas, AC power is becoming available to drivers who wish to 'plug-in' during downtime at travel stops, terminals or even at home on the weekend. Drivers are motivated to plug-in because they see that the 'unlimited' power provided by the electric utility allows continued use of AC appliances without running the truck and without risking battery discharge. For example, when leaving the truck for the weekend, it is more convenient to 'plug-in' than to empty the refrigerator and turn off the DC systems. Driver demand for shore power, plus the positive environmental impact of reduced truck idling, has pushed travel stop owners to consider truck stop electrification in many areas."

* Transparent Transfer Switching: Inverter/chargers have a built-in transfer switch feature that allows connection to shore power without re-routing appliance connections or running extension cords into the cab. This "transparency" facilitates the use of shore power. As soon as power is applied to the exterior AC connection point, (the same as present block heater plugs) the inverter/charger monitors the incoming power quality and automatically connects within 40 milliseconds. If shore power is disconnected (or a "brown or black-out" occurs) the inverter/charger picks up the load within a fraction of a second - fast enough to provide uninterrupted power for most computers.

* Built-in Battery Charger: The charger feature in inverter/chargers improves battery life in three ways: Typical inverter/chargers provide 50 amps of DC output at 12 volts that can keep pace with virtually all DC demands. This eliminates DC loads - such as marker lights or refrigerators - as a source of battery over-discharge. By running DC loads directly, the charger feature reduces the amount of battery cycling imposed by DC systems (both automotive and auxiliary).

According to battery manufacturers, three-stage battery charging with temperature compensation is widely considered to be the best form of charging and is universally considered superior to single-stage charging. Every re-charge with this system actually improves battery state-of-charge and positively impacts the batteries' long-term performance.

Looking Ahead
Is AC power the future for trucking? "We feel it is, no question," says Lawrence. "The majority of truck OEMs now offer AC power infrastructure and shore power connections. I'm convinced that the emergence of an AC infrastructure in trucking is an inevitable evolution of the industry - the benefits are too hard to ignore. When built around a high-quality inverter/charger, these systems will not only improve drivers' quality of life on the road, they will save truck operators significant dollars. In the near future, we expect that the emerging AC infrastructure at truck stops - as well as at home - will benefit progressive truck operators with heightened driver satisfaction, better fuel efficiency and less battery and alternator replacement. In a business where every penny counts, those using AC power will be the winners in trucking's survival of the fittest."