Catching a wave? Hydraulic power generation gradually expanding from traditional applications to include wider range of vehicles; an industry coming of age?

Diesel Progress North American Edition, May, 2004 by Dawn M. Geske

First appearing on the scene in 1969, hydraulic generators have only begun to come of age within the last 10 years. The engineless power units initially found their niche in the fire and rescue industry and more recently have experienced rapid growth into additional markets segments.

The basic premise behind hydraulic power generation is the absence of an engine as the driver. "We're basically eliminating the need for a secondary engine," explained Jim Otwell, president of hydraulic generator manufacturer Harrison Hydra-Gen. Hydraulic generators typically use a vehicle's engine as its main power source, drawing from its horsepower rather than that of an auxiliary, engine power source.

In most cases, a hydraulic piston pump is coupled to a transmission PTO. The pump drives a hydraulic motor, which is used to turn the unit's alternator. The process continues by filtering the hydraulic fluid, cooling it and circulating it back to the pump.

The benefit of such a system, usually applied in vehicles with larger diesel engines, is two-fold. The larger engines are typically not using their full horsepower rating, allowing a higher power draw without creating additional load or sacrificing fuel economy. In contrast, explained Scott Dixon, director of" sales and marketing for Advanced Modular Power Systems Inc. (A.M.P.S.), a hydraulic generator manufacturer based in Sugarland, Texas, "a generator that has a stand-alone combustion engine burns its own fuel, makes its own emissions, has its own maintenance and its own carbon deposits in addition to that of the vehicle engine."

Dixon also noted that maintenance requirements were typically significantly reduced, citing only the need to change hydraulic filters, usually at 200 to 500 hours, depending on the manufacturer's recommendation.

Entirely removing the engine from the generator provides additional benefit in reducing the weight and overall size of the unit. "In the normal gas and diesel generator industry you have a gas or diesel engine to drive the alternator," noted Fred Hartdegen, president of hydraulic generator manufacturer Hart-A-Gen Systems Inc. "In a hydraulic generator you have a very small motor--the size of a football or loaf of bread."

That difference now means that 10 kW can come out of a smaller, 180 lb. package as opposed to a 550 lb. engine gen-set and the package size is dramatically decreased, said Hartdegen. This allows the unit to be mounted almost anywhere, freeing up interior space, a precious commodity in emergency vehicles.

While the first hydraulic generator is believed to have originated for the oil industry over 30 years ago, it wasn't until the early to mid-'90s when more companies began to manufacturer hydraulic gen-sets. Harrison Hydra-Gen, headquartered in Houston, is generally considered the founder of the hydraulic power generation technology seen today, as it holds the first serialized records of a hydraulic gen-set produced for Schlumberger Limited, a New York oil field services company. Schlumberger wanted to equip its oil patch trucks with a gen-set that fit within a small space. The answer turned out to be Harrison Hydra-Gen's first hydraulic generator.

"Its been going great, we've grown tremendously over the last five years," said Otwell. Harrison Hydra-Gen's line of hydraulic generators ranges from 5 to 30 kW. Its product line features the HAS series, a line of small- end generators 10 kW and below with primary application in hand power tools and light towers for the construction and utility industry. The MAS series are capacitor controlled generators with Gillete coiled, two-pole alternators.

Harrison Hydra-Gen's range also includes the 10 kW and above MPC series, its core line designed over 30 years ago for oil fields, marine and export industries. The MPC series are voltage regulated generators designed to provide constant power using a four-pole industrial alternator coiled by Newage, a subsidiary of Cummins Inc.

The typical mounting for the MAS and MCP generators is off the vehicle PTO, but they can also be attached directly to the transfer case or off the front of the engine. Harrison generators are driven by Bosch Rexroth and Kawasaki pumps.

Nearly 20 years after Harrison Hydra-Gen began manufacturing, a number of other hydraulic power generation manufacturers began to emerge. A.M.PS. began production of hydraulic generator systems in 1992 and according to Dixon, the growth of the company, "from conception to current state was probably 1000%."

"In 1997 we were selling 15 units a month," he noted. "Last year it was 80 to 90 units"

A.M.P.S.' generator line includes the eHP scries, a range of 6 to 30 kW single- and three-phase generators target ed toward the fire, oil and gas and marine industries. The el IP series is standard with an electronic digital controller to monitor and control the generators' system performance in ac volts, frequency and two-line amps. The eHP series is driven by a Bosch Rexroth hydraulic pump, typically mounted directly to the PTO or to a bracket behind it.