Electric Power Gives New Life to Aging 20-Ton Crane

The time had come for American Crane Rental, Manteca, Calif., to make a decision about its 1999-vintage Shuttlelift 7750RT rough-terrain crane.

The compact, 20-ton-capacity, crane had provided years of good service to American Crane’s customers, both as a maintained and bare-rental machine. Its structural components were still solid, but some of its systems were due for overhauling, and the California Air Resources Board (CARB) had said its diesel emissions were higher than allowed.

American Crane Rental had to decide whether to invest in significant overhauls or to buy a new crane to replace the 7750RT.

If the company decided to replace the aging Shuttlelift rough-terrain crane, American Crane’s founder and owner, Keith Powell, had to decide whether to replace it with another diesel-powered rig or to buy a battery-powered hybrid crane that could meet growing demand for exhaust-free lifting equipment to make lifts inside factories, warehouses, and other enclosed job sites.

Thinking creatively, American contacted Bailey Specialty Cranes & Aerials, Muskego, Wis., to see whether converting the aged but sturdy Shuttlelift RT to hybrid electric power might be a more economical way to meet the need for exhaust-free lifting than investing in a brand new crane.

Bailey’s analysis showed that converting the 7750RT to run on DC power would cost about 60% less than buying a brand new machine.

Jeff Bailey, president of Bailey Specialty Cranes, said, “Typically, this kind of conversion from diesel to hybrid electric power involves an older crane. It enables an owner to serve specialized customers while getting a good return on an existing asset.”

Converting American Crane Rental’s Shuttlelift 7750RT to hybrid electric power involved replacing the 130-hp diesel engine, transaxle, and five gear-type hydraulic pumps with a set of 1,000Ah lead-acid batteries; two 35-hp 80V variable-displacement pumps with gearboxes; two additional reduction gearboxes; an LP-gas-powered generator; and Bailey’s computerized control system, which included a load-moment indicator.

Bill Cavros, Bailey’s chief engineer, led the conversion project. “This three-month project gives new life and usefulness to a machine that might have been written off.”

Cavros gave credit to engineers at Manitowoc Cranes, which now owns Shuttlelift, for their help in providing specifications for the 17-year-old crane.

The new hybrid electric system gets its power from a set of 80V, 1,000Ah, tubular-plate, lead-acid batteries that can be recharged either by the LP-gas-fueled onboard generator or by plugging into three-phase 220 or 460 power. To simplify maintenance, the automatic watering system not only monitors the batteries and fills them when they need it, but also tells the operator when watering is complete.

“This is a series hybrid system,” says Cavros. “The generator’s only job is to recharge the batteries, not to provide power to run the crane.” That means the generator can be small enough to be economical, yet recharge the batteries from 20% to full charge in about eight hours.

“It’s fairly common for a user to park the crane outside and let the LP generator recharge the batteries during overnight,” said Jeff Bailey. “The generator will run until the batteries are fully charged and then shut itself off.” The crane and generator are unlocked with two separate keys, so it is possible for the generator to operate while the crane itself is locked and the key removed to prevent operation.

The LP-fueled generator is equipped with a catalytic converter and oxygen sensors. It meets the emission standards of all 50 states, including California’s stringent regulations.

Pumping up efficiency

To use the battery power most efficiently, Bailey replaced the crane’s original five gear pumps with two 35-hp, variable-displacement axial-piston pumps with integral gear boxes and brakes. The pumps are from Oilgear and the motors are Danfoss H1 series.

The new pressure- and flow-compensating pumps deliver up to 45 gal. of flow per minute, but only put out the amount of pressure and flow needed for the functions in use.

For even better economy and function accuracy, the system’s hydraulic valves are both pre and post compensated. That efficiency lets the batteries deliver longer working cycles between recharging. Cavros says that in typical use, customers usually get about one to two days of work per charge.

The pumps power the Danfoss H1 series hydraulic motors that drive the front and rear axles through additional reduction gear boxes with integral brakes. The pumps also power the motor for the hoist winch, the motor for swing, and the hydraulic cylinders for boom raising and extension.

Swapping two exhaust-free 35-hp electric motors for a 130-hp diesel engine requires some tradeoffs. Those exchanges come in top travel speed and function speed at higher loads.

Although top travel speed is reduced from 20 mph with the diesel to five mph with the electric drive, the electric-powered 7750RT can climb the same 63% grade as the crane could when powered by the diesel engine. The oscillating rear axle gives excellent traction on rough ground, and can be locked to provide maximum stability for lifting.

Bailey’s electrically powered version of the Shuttlelift 7750RT delivers the same swing, boom-extension, boom-raising, and hoisting speeds as its diesel counterpart at up to 25% of maximum load. At full load, it operates about half as fast as the diesel-powered crane. “In everyday lifting, the operator won’t notice the difference,” says Cavros.  

New control system plus LMI

The Bailey computerized control system uses electric-over-hydraulic, piloted joystick controls along with pre- and post-compensated Sauer Danfoss hydraulic valves that deliver just the pressure and flow needed. The system also includes a full-color display whose six screens show information from the rated load indicator as well as diagnostic information. The load-indicator system gets its load-on-hook information directly from a load cell on the hook, which Jeff Bailey says is the most accurate method of measuring. The system also uses angle and length sensors on the boom to make its calculations. All of the sensors are LSI brand radio units, which minimizes the need for new wiring to install the LMI.

After the conversion, Bailey put the revitalized rig through the full battery of tests needed to meet the ANSI B30.5 code.

Although American Crane Rental’s 20-ton Shuttlelift 7750RT is the largest rig that Bailey has converted, Jeff Bailey says that his company has more than a decade of experience doing that kind of work. The first machine it converted was used by an aircraft manufacturer to handle sections of fuselage during production.

Bailey says customers tell him that once customers who need exhaust-free lifting find out that electrically powered cranes are available, rentals peak up, and so do rental rates.

Everett Powell, co-owner and vice president of American Crane Rental, said he expects the electrically powered Shuttlelift 7750RT to stay busy. “We have a propane-fueled 15-ton rough-terrain crane that is always busy,” he said. “Customers like its ability to work in closed spaces without diesel fumes. The converted Shuttlelift has five more tons of capacity and can work exhaust free, so I expect it will stay busy, too.”

Said Bailey, “Converting an older, structurally sound, crane from diesel to electric power can help an owner get more useful life and income from a machine they already own.”

Founded in 2002, American Crane Rental operates a fleet of 43 units that serve California’s central valley and San Francisco Bay area.