Cool Tools: Portable Generators
Published: June 2012
Compact generators are one of the most-used types of equipment on electrical projects, providing temporary power sources on job sites where commercial power is not yet available or not readily accessible, for jobs to restore power in commercial and industrial locations, and in emergencies.
“Electricians demand reliable and smooth power when choosing a generator. Time is money on the job, requiring a generator that will do the job without any down time or need for repair,” said Sara Pines of Honda Power Equipment Public Relations. “Also, having equipment that provides stable voltage is key during generator operations.”
Compact, easy-to-move portable generators provide the electricity for work lights; to power tools and to recharge batteries of cordless tools; to electrify portable heaters in the winter and fans in hot weather; and to power lights, computers and other equipment in on-site mobile offices. A wide choice of portable generator models is available with a broad range of power output capacities. The smallest models can be picked up and moved by one person. Larger single-axle trailer-mounted models provide more power for various needs, including operation of temporary lighting in outdoor areas.
Many contractor companies and facilities own one or more generators in different sizes, while late-model portable generators are readily available at general rental centers and equipment rental specialists.
Pines said the Honda Power Equipment (www.powerequipment.honda.com) line of portable generators ranges in capacity from 1,000 watts (W) to 10,000W, with units in the 3,000W to 10,000W range most popular for commercial applications and rental center operations.
The focus of the latest compact generator models, Pines said, is to provide excellent fuel economy and advanced features, such as digital automatic voltage regulator (DAVR) technology for increased performance.
“DAVR holds the voltage stable within 1 percent over time during standard operation and has a built-in self-diagnosis function to prevent engine speed from exceeding 4,140 rpm for longer than three seconds and abnormal voltage,” she said. “In addition, the DAVR adjustments are driven off the main winding, as compared to a sensor winding in conventional AVR [automatic voltage regulator] systems.”
To get the most efficiency and ensure safe use, it is important to evaluate the requirements for which a generator is to be used and to match equipment with those requirements.
First, consider the highest power application that will be operated by the generator and the type of load the generator will serve. There are two types of loads: reactive and resistive.
Reactive loads (tools and other devices with electric motors) require three times the power at start up than during regular operation. Therefore, the power required to start the capacitor motor on these applications will determine the rated power of the generator for the application. When determining the proper generator for reactive loads, three modes of operation must be considered: starting power needed, power required to run the motor once it is started, and loaded power requirements necessary when the tool begins to work—e.g., when a saw begins to cut or a drill penetrates material. Capacitor motors can take three or more times additional power to start than to operate. Universal motors require one-and-a-half to two times more current to start.
If a generator has the power to start a load, usually it will be able to power it continuously. If more than one piece of equipment is to be operated, estimate the starting and running load of the largest piece of equipment. Provided two tools are not started at the same time, the generator will be able to start and run a second tool of lower wattage.
Resistive loads (lights, devices without motors, etc.) require the same amount of power to start and run.
Honda recommends a generator never be operated at its maximum power output for more than 30 minutes. Rated power, or the power that a generator can produce for long periods of time, is a more reliable measurement of generator power. Typically, rated power is 90 percent of maximum power.
Pines said, when a generator is to be used for computers or sensitive electronic equipment, it is important to determine whether a generator incorporates inverter technology. Inverter technology takes raw power produced by the generator and passes it through a microprocessor that provides power with a sine wave similar to alternating current.
“Inverter technology is stable power that can be delivered in a small and light package and allows the most sensitive of electronics to be operated without fear of interruption,” Pines said. “Specifically, inverter generators offer clean power or electrical current that is consistent and has a stable signal or sine wave.”
A computer without clean power would likely freeze or shut down, or its operation would be interrupted.
Inverter technology also allows portable generators to be substantially lighter in weight and smaller in size by eliminating a standard alternator.
A significant number of portable generators on job sites today—electrical and other—are rented.
“In the past several years,” Pines said, “an increasing number of independent or smaller contractors and commercial generator users have turned to rental stores for their product needs, rather than purchasing their own units. Traditional generator purchases are still strong for commercial users, yet rental stores comprise a healthy share of industrial generator purchases.”
United Rentals (www.ur.com) is the world’s largest renter of construction equipment, and portable generators represent a significant segment of its business.
Construction sites typically demand a lot of electricity because of the need to power tools and site lighting at all stages of a project, said Matt Thomas, United Rentals sales and marketing manager for power and HVAC equipment. The testing process also creates large power needs—for example, the testing of elevators, electrical systems and mechanical systems.
A fair estimate of the number of rented generators on job sites would be in the range of 10 to 15 percent, Thomas said. However, while every job site may use a generator, electrical contractors are not the only ones using portable generators.
“In our experience, 6-kilowatt [kW] gas portable models up to 100 kW diesel towable units are those most often rented by electricians. Contractors are interested in sound quality, meaning how quiet the unit is, and power quality. New inverter series units are high profile right now—the technology is quieter to operate and reduces energy consumption. We’re also seeing demand for units with self-contained environmental basins; the basin keeps fluids away from the surrounding environment in the rare case of a mechanical failure,” Thomas said.
Generator rentals range from days to weeks, he said.
“There’s no strong skew toward one end of that range or the other. Each site is different, and the need for temporary power often depends on the local utility’s ability to provide a temporary power pole.”
Thomas said the biggest change in larger generators is meeting Environmental Protection Agency (EPA) Tier 3 and Tier 4 emission standards for off-road equipment powered by diesel engines.
Regarding emissions, Honda does not produce any diesel-powered generator products, so Tier 4 is not a consideration, Pines said.
“In relation to all other emissions regulations for gas powered portable generators, Honda is committed to meeting or exceeding all EPA and CARB [California Air Resources Board] emissions standards for all of our products,” she said. “We are always working to design new products that will utilize new innovations to further reduce all types of engine emissions. As a specific example, our newest generators incorporate a fluorine fuel tube and canister system along with a tethered chain-type gas cap to meet current EPA evaporative emissions regulations.”
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at firstname.lastname@example.org.