VANCOUVER, B.C. - Electrical systems have become a focus for OEMs as well as truck drivers. Why? As engine-off electrical loads have increased, the old electrical systems are hard pressed to keep up -...
VANCOUVER, B.C. – Electrical systems have become a focus for OEMs as well as truck drivers. Why? As engine-off electrical loads have increased, the old electrical systems are hard pressed to keep up – and that can lead to premature failure. In the heavy truck industry, it is not uncommon for batteries to last less than expected, and many alternators don’t make it past their warranty period.
According to Bruce Purkey, president of Purkey’s Electrical Consulting, the primary culprit for early death is a poor battery maintenance program combined with uncontrolled discharge of the vehicle’s batteries, which makes the electrical system work harder. “What’s also contributed to the problem is the exploding growth of inexpensive consumer-grade inverters, which convert DC power to AC for onboard electronics,” he emphasized. “They’ve added current draw on battery packs that in many cases are already suffering from poor battery maintenance.
“Today, a truck is much more than cab and trailer. Drivers want to bring the comforts of home with them on the road. When they do, it can spell trouble for fleets that do not properly design their electrical systems for the use of inverters. For example, many drivers will use DC refrigerators and low-quality inverters to run various AC devices. The combination of uncontrolled loads coupled with the other loads drivers have on when the engine is off can draw down batteries to levels that can quickly ruin their ability to start the engine. The reason is that low-grade inverters offer little – if any – protection from drawing a battery too low. If they have any protection, it is to protect the inverter’s electronics, not the vehicle’s batteries. The more often this occurs the battery pack will lose capacity and not provide the expected service,” Purkey explained.
“The adage ‘you get what you pay for’ is especially true with inverters,” acknowledged Brian Lawrence, heavy duty truck manager for Xantrex Technology.
“The cheaper inverters are, typically the less protection you have. Without adequate ‘shut-off protection’ – which low end units usually are – a frenzied alternator will have to work overtime, potentially resulting in shortened life.”
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 said. “At idle and high loads the alternator is not turning very fast, and therefore not pulling a lot of cooling air through the alternator. This high heat and low air flow for cooling can cause issues. 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 could be shortened and again, the capacity of the battery pack can be seriously compromised. At Xantrex, we are finding that many fleets and owner/operators are expending batteries three to four times faster than necessary, and burn through twice as many alternators as they should.”
For many trucks, this equates to premature failures that can cost hundreds, if not thousands, of dollars in parts replacements. But, more importantly, said Lawrence, it can mean lost productivity and missed deliveries.
Why batteries die
Purkey and Lawrence suggest that there are some major contributors to poor battery life in heavy trucks:
Uncontrolled discharge: Deep discharge does irreversible damage to engine starting batteries on a fundamental physical/chemical level. Each discharge below 50 per cent capacity negatively impacts longevity. Each discharge below 75 per cent discharge is so harmful that just a handful of such events can drastically reduce the useful life of a battery. A battery, no matter how well maintained, has a finite number of charge/ discharge cycles (Ref; SAE J2185 deep cycling test). Routine cycling, even as modest as 25 to 30 per cent depth of discharge, will deplete the number of cycles the battery has available to give over its useful life.
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 chemistry and temperature.
Truck charging systems typically rely on single stage charging, which has traditionally been adequate for starting systems. However, this is often not the optimal method for recharging heavily discharged batteries.
Increasing battery life
Any solutions for increased battery life? “There are,” said Lawrence. “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” Controlled Protection (Low Voltage Disconnect): The best inverter/chargers have sophisticated smart load controlled 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. 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.
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 for quality and automatically connects after approximately 45 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 OEM 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.
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