July 22, 2013
material handling update | Batteries/Chargers

Battery room confidential

Battery room confidential

Many different factors can detract from lift truck battery performance—including a few you might not have thought of. Industry insiders tell us what to watch for.

By Toby Gooley

In some warehouses and DCs, lift truck batteries are taken for granted. Much like car batteries, they're treated as something that can essentially be ignored until there's a problem. But a lift truck battery is not a "set it and forget it" piece of equipment. Rather, it's a complex device powered by electrochemical reactions; compromise the battery's ability to efficiently produce those reactions and you'll diminish its performance and lifespan. Indeed, the key to getting superior performance from a lift truck battery, says Harold Vanasse, vice president of sales and marketing for battery management systems supplier Philadelphia Scientific, is to understand the following fact: "The laws of physics can't be violated!"

Not everyone understands that, though. As a result, some of the many factors that can detract from battery performance tend to get overlooked. Want to know what you may be missing? Here's advice from industry insiders on what to watch for—including a few things you might never have thought of.

Temperature. Temperature—both high and low—has an enormous impact on battery performance. As you might expect, a battery can be destroyed if it should freeze. But even moderately low battery temperatures will decrease capacity. At 30 degrees F internal temperature, the available battery capacity is reduced by roughly 30 percent, says Bill Rubenzer, vice president, sales and marketing at industrial battery manufacturer Storage Battery Systems LLC. Even at 50 degrees internal temperature, a 1,000-ampere-hour battery will act more like a 600-700 amp-hour unit, according to Tony Amato, executive vice president of battery distributor Industrial Battery Products Inc.

When the battery temperature falls below 40, the voltage will appear artificially high and a battery discharge indicator (BDI) will show more power available than there actually is, says Steve Spaar, marketing director-Americas for the battery manufacturer EnerSys, which also owns Douglas brand batteries. At low temperatures, the charger will also see the voltage as artificially high and will shut off too soon, which leads to shorter battery life.

There are ways to counteract the effects of frosty temperatures. One option for extremely cold environments is to insulate the battery compartment. Another is to use a battery with a high amp-hour capacity. It's possible to raise that capacity in an existing battery by increasing the acid content in the electrolyte solution (the mix of water and acid that governs the battery's electrochemical reaction and thus, its voltage). However, Amato warns, there's a trade-off: You'll get more run time per shift, but you'll also be shortening the battery's useful life by potentially as much as two years.

A battery with tubular positive plates will have more usable capacity than an equivalent flat-plate-construction battery, and so should be considered for cold applications, Rubenzer says. Not just batteries but also chargers should be specifically designed for low temperatures, and battery discharge indicators should be adjusted for cold conditions.

Sustained high battery temperatures can do serious damage. Battery life can be reduced by as much as 50 percent for every 15-degree increase over 77, based on average temperatures. As a battery's sustained temperature increases, moreover, the loss of battery life accelerates.

Battery heating is caused by the resistance of the intercell connectors while a vehicle is in use, according to PowerDesigners, a manufacturer of battery chargers and monitoring systems. Additional heating due to this same effect occurs during charging, and the higher amperage used during opportunity and fast charging exacerbates the problem, the company says. Because there's no cooldown period following the charge, as in a conventional charging application, the battery remains hot.

Hot air temperatures can also lead to overheating, especially in fast and opportunity charging operations. Power Designers explains it this way: While it is in use (i.e., being discharged), a battery usually will be warmer than ambient temperatures. As the ambient temperature rises, the air becomes less effective in cooling the battery, and the battery's internal temperature will rise. Charging will further raise the battery's internal temperature—possibly to the point where the battery could suffer damage if you're not careful.

For example, discharging typically adds about 15 degrees to the battery temperature. At an ambient temperature of 75, then, discharging will add enough heat to raise the battery's temperature to 90. Charging will add another 10 degrees, bringing the battery's temperature to 100. When a battery reaches 130 degrees, the charger will issue a "battery over temp" fault and will stop the charge to prevent battery damage. In this case, the battery has a margin of 30 degrees before that happens. But at an ambient temperature of 90, the battery begins charging at 105 degrees (90 + 15). The added heat from charging (10 degrees) coupled with the reduced cooling effect of the higher ambient temperature could potentially cause the internal temperature to rise high enough to trigger a "battery over temp" fault.

Making sure battery charging areas are well ventilated to provide good air movement will help to minimize average battery temperatures, according to Aerovironment, the manufacturer of PosiCharge fast charging systems. For battery changing systems, make sure there is a cooldown period after charging and use a first-in, first-out (FIFO) rotation. For opportunity charging, consider using ventilated battery trays or some type of active cooling, such as blowing air.

Temperature will affect cells differently depending on the battery layout or position in the lift truck, causing some cells to be overdischarged while others are underdischarged, notes Ken Sanders, director of motive power battery engineering for East Penn Manufacturing Co. Inc., maker of Deka brand batteries. A weekly equalizing charge—an extra-long charge that brings each cell in the battery up to the same, maximum capacity—will allow battery and cell temperatures to reach a state of equilibrium, thus minimizing cell-to-cell temperature variations and improving battery performance and longevity, he says.

Failing to equalize. Batteries should be equalized once a week, says Amato. Unfortunately, that doesn't always happen as scheduled, due to poor maintenance tracking or because with chargers that are set to automatically do an equalizing charge, users tend to assume that everything is happening as planned. But that's not always a safe assumption, Amato warns. In a facility that rotates multiple batteries, "the batteries don't always get on that charger the right day or time," he says. A battery tracking and monitoring system that alerts managers when a particular battery has not been equalized is one possible solution.

Improper watering. Overwatering, underwatering, or watering at the wrong time will lead to a host of problems that can shorten battery life. These include plate oxidation and capacity loss; inadequate electrolyte levels; drying out and overheating; reduced amp hours, which can lead to overcharging and overheating; and boilovers, resulting in acid damage to battery tops, equipment, and floors (and potentially personnel) and requiring a costly acid adjustment.

Battery manufacturers recommend filling after an equalizing charge. Because the electrolyte expands when the battery is in use, watering after a charge helps to prevent overfilling and boilovers, say the folks at Flow-Rite Controls, a supplier of battery watering systems. It's best to fill on a regular schedule: weekly for heavy-use applications and less frequently (perhaps as little as once a month) for light-use applications.

Manually filling individual cells correctly—adding neither too much nor too little—is not easy, and the process typically takes around 15 minutes. Single-point watering systems maintain reliable electrolyte levels and take less than a minute, according to Flow-Rite and other providers of watering systems. These systems consist of automatic shut-off valves connected to tubing, which replace the battery's vent caps. Once the tubing is connected to a water supply, water flows into each cell until it reaches the correct level. When using a single-point watering system, be sure to regularly check the system valves to prevent potential clogs.

Overdischarging. Regularly overdischarging—allowing a battery to dip below 20 percent state of charge—will damage the battery, causing premature capacity loss and shortening its lifespan. One increasingly common reason operators overdischarge batteries is that lift trucks are traveling faster and are lifting heavier loads higher and more quickly than in the past, which places greater demands on the battery. This is particularly true of trucks with the newer alternating current (AC) motors, which pull more current out of the battery than their direct current (DC) counterparts. "You're getting 10 to 15 percent more work out of [an AC] truck, but the battery technology is still the same," Amato says. "That means you're using 10 to 15 percent more power in the same time frame."

If the battery isn't sized to meet that extra demand, "the battery will draw down to a 20-percent charge sooner than you would see with a DC truck," says Spaar of EnerSys. "So if you're lifting high at the end of a shift, it could put you over the limit." Larger-capacity batteries designed for AC trucks and "lockout" systems that prevent lifting if the state of charge gets too close to 20 percent will help prevent overdischarging.

Overdischarging can also happen when lift truck operators in a facility that uses opportunity or fast charging cut short or skip scheduled breaks. Those breaks are essential windows for charging batteries; operators who miss some breaks are likely to run batteries down below the minimum before their shifts end, says Aerovironment. Making break schedules mandatory and using a properly sized charging system will help to prevent this problem.

Moisture. Moisture can cause corrosion on the battery connectors and tray, which allows voltage leakage from the battery to the frame of the lift truck—a situation that can cause the truck's electrical system to ground fault, says Sanders. Moisture, by the way, is not just a problem in hot, humid climates. It can also become a problem when batteries are overwatered or when the fans in high-frequency chargers draw in moist air and blow it over batteries and associated electrical components.

The best method of preventing humidity-related corrosion is a simple one: keeping the battery tops as clean and dry as possible. Rubenzer of Storage Battery Systems also recommends fully insulated, bolt-on cables, which are less susceptible to moisture-related corrosion. Be sure, too, to keep high-frequency chargers away from wet or washdown areas, he says.

"Parasitic" loads. Some integral devices and optional features, such as heaters, fans, and GPS, get their power from the same batteries that power the lift truck. While the energy draw of any one device may be low, a battery under such constant "parasitic" loads may require a refresh charge more frequently to counteract the higher battery self-discharge rate, says Sanders. This will negatively affect performance and life. To reduce or eliminate the need for refresh charges, be sure to use a battery with enough capacity to handle the total demand for an entire shift.

Outdated chargers. Technological advances mean that today's lift trucks—and the demands they place on batteries—are different from those of a decade ago. Yet many people who regularly update their forklifts have 10- or 15-year-old chargers, notes Amato. "Some of the outputs of those chargers have not kept up with the requirements of today's battery," he says. He recommends verifying that existing chargers are adequate for your current battery applications.

Pushing loads, driving uphill, and heavy lifting. Regularly driving up inclines, pushing loads (long frowned upon by lift truck manufacturers), and high lifting of heavy loads can quickly drain batteries while placing physical strain on trucks. There is no adverse effect on battery service life, but the kilowatt-hour consumption is higher and the battery should be sized accordingly, Rubenzer says. If those activities occur daily, consider using the highest ampere-hour-capacity battery available, he adds.

THE POWER OF PREVENTION
Lift truck batteries are designed to work for five years, or 1,500 to 1,800 cycles, assuming they are used and maintained correctly, says Vanasse. "If a battery doesn't last that long, then it's probably your own fault," he observes. That's why the experts we consulted for this article agree that regular preventive maintenance (PM) is a must for maximizing battery life and performance.

Even fleet managers who scrupulously follow a PM schedule for their lift trucks may not do the same for batteries. But batteries are costly and they're critical to an operation's productivity, so there should be a regular PM schedule in place to make sure they're getting cleaned, equalized, and watered appropriately, says Power Designers.

For many fleets, the most effective way to do that is to use a battery monitoring system that collects data, issues alerts, and creates reports on such things as cycles, equalization, watering, temperature, and state of charge. "In the past, you wouldn't recognize a problem with a battery until it was too late," says Spaar. "You could go a year or more before seeing a fall-off in performance. With the information systems available now, you can know the same day when somebody didn't water properly or overdischarged."

In Vanasse's view, monitoring systems are invaluable tools for both battery and fleet management. "If you don't measure and make use of that data, you can't improve anything," he says. Put that information together with a preventive maintenance program, and fleet managers can take a much more active role in extending the life of their batteries.

About the Author

Toby Gooley
Senior Editor
Before joining DC VELOCITY and its sister publication, CSCMP's Supply Chain Quarterly, where she serves as Editor, Toby Gooley spent 20 years at Logistics Management covering international trade and transportation as Senior Editor and Managing Editor. Prior to that she was an export traffic manager for 10 years. She holds a B.A. in Asian Studies from Cornell University.

More articles by Toby Gooley

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