The power-shovel industry saw a somewhat revolutionary transition in the 1910s. Steam, the standard power source for these machines since their advent around 1835, was being challenged by the new technology of electricity. The Osgood Dredge Co. in 1898 developed the first electrically powered excavator, and Vulcan Iron Works, Toledo, Ohio, had an electric model commercially available in 1899.
Although these early designs made clear the advantages—at least in principle—of electricity over steam, not until development of the Ward-Leonard DC control system did the concept become practical. This system used an AC-powered motor-generator set and DC motors to drive excavator functions, producing variable speed under exact control and allowing maximum load on the motor at stall speed without burnout from overload.
The electrically powered excavator, unlike its steam counterpart, did not demand that huge quantities of wood or coal and water be continuously supplied to remote and scattered sites, through mud and ruts, probably by mule and wagon, because trucks capable of making these deliveries were still years in the future.
Even if a reliable water source were near by, the water usually required expensive treatment with softeners, filters and purifiers. Adding further to the cost and inconvenience of steam were the necessities of periodically cleaning boiler tubes and draining the boiler when freezing weather was expected after machine shutdown.
By contrast, early electric excavators could use electricity from a power plant at relatively low cost, or, lacking that, an on-site steam generator could be used. The latter involved costs for construction, fuel and water, of course, but these costs were comparatively low, because supplies could be delivered to a central, accessible site. Quarries, in fact, were already using electricity to power crushers, conveyors and other stationary equipment, so electric excavators were marketed to these operations on the principle of simply plugging them into the existing grid.
Other advantages of electrically powered excavators included instant availability—no waiting for pressure to build—and clean running. Even in the early 1920s, many cities had ordinances against excessive exhaust smoke, and boilers of all sorts were falling under tighter regulation, which could involve costs for making the boiler compliant—or for fines if it didn’t comply. Also, steam engines required that complex mechanical drive systems be used to deliver power to the machine’s various mechanisms, but electric machines could use a relatively simple system of cables and drive motors.
Although internal-combustion engines eventually dominated the design of construction excavators, electricity became the standard for draglines and cable-operated shovels in the mining industry—a power system that traces its roots to the small electric excavators of the 1910s and 1920s.
The Historical Construction Equipment Association (HCEA) is a 501(c)3 nonprofit organization dedicated to preserving the history of the construction, dredging and surface mining equipment industries. With more than 4,000 members in 25 countries, activities include operation of National Construction Equipment Museum and archives in Bowling Green, Ohio; publication of a quarterly magazine, Equipment Echoes, from which this text is adapted, and hosting an annual working exhibition of restored construction equipment. Individual memberships are $32 within the U.S. and Canada, and $40 elsewhere. Information is available at www.hcea.net, 419.352.5616, or i[email protected].