AC power to the lift truck

First introduced to the U.S. market two years ago, AC electric lift trucks are powering their way into warehouses and factories.

Modern Materials Handling - May 1, 2002

Until most recently, there was only one option for North American buyers of electric-powered lift truck engines – DC power. Even though AC power had long been available in Europe, it wasn't until two years ago that lift truck buyers here had that option or the benefits that go along with it.

Since then, AC has gone from a novelty (only Toyota offered it initially) to a standard offering from several suppliers with others indicating that they will soon launch their own versions. Furthermore, AC power is now available on different types of lift trucks including counterbalanced, narrow-aisle reach and hand pallet models.

Exactly how big AC-powered lift trucks will get is an open question at this point. But there does appear to be momentum despite the doldrums that the overall lift truck market finds itself in these days. And with good reason.

AC power offers several improvements over traditional DC. To begin, AC-driven lift trucks maintain their battery charge longer than DC. That allows AC trucks to operate at peak power for longer, improving productivity. In addition, maintenance requirements are reduced, cutting time and costs. As end users are finding, that combination is meeting some key requirements in a tough economy (see side bar boxes below - Moving steel in 40 foot lengths more easily and Moving paper is more efficient with AC power ).

What AC power is worth

For all of its differences, AC-power technology still requires a DC battery. Electrical power flows from the battery to an inverter that converts the energy to a three-phase current. This power is then directed to the lift truck's travel motor, controlling speed and acceleration, and to the load handling motor, controlling load movement.

As a result, acceleration and torque are greater. There is also a faster, smoother response when the operator changes lift truck direction. Furthermore, AC lift trucks have more power when climbing a grade.

Typically, a battery of 48 volts or larger is required. That means current users of 36-volt batteries will usually need to invest more in the larger batteries. Some of the heavier-duty models from Europe use 80-volt batteries.

Performance remains high even as battery power continues to drain. Until the battery hits 80% discharge, performance is said to remain at 100%, which is beyond the capabilities of DC power.

Interestingly enough, power is not simply drained during use. It can also be regenerated. This primarily occurs during braking but also when the operator switches between forward and reverse. Power regeneration occurs when the accelerator is released and the truck is coasting as well as when the brake is applied. While this extends battery run time, it is not a substitute for battery recharging

The end result is a longer time between battery charges with AC than DC, when both are used comparably. This extends truck run time between charges, making the vehicle available for longer uninterrupted periods of time out on the shop or warehouse floor where it is needed.

Another feature of AC systems is cooler running motors, which has two benefits. Because less energy is lost as heat, the AC system is more energy efficient than DC. Additionally, there is less concern about heat-related issues with other lift truck components such as wiring.

Lower maintenance requirements are still another distinction of AC systems. When the first AC models were released in the U.S., there was some discussion as to whether maintenance advantages were real or not. That, however, has dissipated, an important shift given the typically higher initial cost of AC trucks.

"Over time, the true operating costs of an AC-powered truck offsets the initial cost," says Dirk von Holt, president of Jungheinrich Lift Truck Corp. "And most end users will recognize a significant cost savings," he adds.

Looking over a 10-year service period on a four-wheel electric counterbalanced truck, von Holt places the replacement parts cost savings alone at $3,200. Those savings are possible because AC systems do not have brushes or contactors that need to be replaced regularly. Additional savings are realized from lost time due to maintenance schedules and related activities.

Overall, "AC technology offers significant advantages to end users," explains Jim Malvaso, president of Raymond Corp. These advantages include higher overall performance, higher productivity and lower cost for each load handled. Malvaso cites greater operational efficiencies and lower operating costs as the bottom line with AC-powered lift trucks.

But as Kim Wanamaker, vice president of marketing and sales at Drexel Industries, points out, comparable AC and DC trucks can be designed and used for various applications. "It's important to remember that AC versus DC offers certain advantages but is seldom a primary reason for a particular model/truck selection for an application," says Wanamaker. "Many other product capabilities and functionality of trucks being considered should weigh more heavily on decisions."

Options in AC trucks

While no longer the only AC game on the continent, counterbalanced models still dominate these offerings two years after Toyota brought the technology to the North American market. Additionally, AC is available with various reach truck models, both pantograph and moving mast type, as well as hand pallet trucks.

Meanwhile, Toyota has expanded its initial offerings. Its pneumatic-tire, all-electric 7FB models were joined last year by an expanded 7-Series lineup. These cushion-tire trucks combine AC with Toyota's System of Active Stability (SAS) that reduces the risk of tip overs. "The performance of these AC trucks rivals that of most engine-powered lift trucks," says Brett Wood, national product planning and research manager at Toyota.

Additional counterbalanced offerings are from Jungheinrich. The EFG family features 2,000, 3,000, 5,000 and 6,000 pound models. Travel speeds compared to DC models are said to be 10% higher while lift speeds are 15% higher. Recommended servicing levels are every 1,000 hours or every six months.

Narrow-aisle reach trucks have also entered the picture. First offered in North America by Drexel, these models initially extended the reach of AC into applications previously closed out to counterbalanced and hand pallet trucks. Drexel's offerings include the MDR- 45 and 55 narrow-aisle truck for long awkward loads that must be handled in aisles as narrow as 94 inches. The three-wheel vehicle features four steering directions including side travel and circle mode. Other entries include the DXR 45 and 55 sit-down reach trucks with lift heights to 31 feet and a top end capacity of 5,500 pounds.

The most recent entry into the AC fray is Raymond. Earlier this year, Raymond introduced what it calls the first AC-powered reach-fork truck designed and built in North America. The Accelerated Cycle Reach-Fork Truck, also known as ACR, combines Raymond's Easi control system with its intellidrive system for top speed and acceleration. The ACR family includes deep-reach, side-stance, four-direction and cold-storage-proven models.

The first hand pallet truck with AC power was introduced to the North American market in late 2000 by Multiton MIC Corp. The EME 30, as a replacement for manual pallet trucks, is for horizontal transportation of loads. It features a maintenance-free gel-cell battery pack and an on-board charger.

In all likelihood, these will not be the only AC offerings in North America. By all indications, this technology is not only here to stay but poised for future growth.