Cool Tools: Portable Power
Published: June 2008
Portable power systems remain one of the most essential items in the equipment fleet of electrical contractors.
Compact generators provide needed power on projects when conventional power isn’t available, for maintenance work when facilities lose power and after disasters allowing rescue and restoration work to progress before electrical service is restored. Versatile generators come in a variety of sizes, power tools and temporary lighting, and operate computers and other equipment in mobile offices.
Portable generators are available in many sizes, from compact models that fit in the trunk of a car to larger trailer-mounted models. Output of portable generators varies widely, starting at 4 kW and going up to large units producing as much as 5,000 kW or more. Units producing from 50 to 100 kW are popular choices and are available with a variety of features. Depending on the model, both single- and three-phase power can be developed, and some units permit the use of small tools at the same time the generator is producing three-phase power. Packages such as portable light towers, including both generator and lighting components, are popular with electricians.
The latest portable generators are smaller and lighter than earlier models, are more fuel efficient, and they run quieter than older models. Inverter generator technology allows a generator’s engine to run only at the rpm needed to power the load, saving fuel and reducing sound levels. Full ground-fault circuit interrupter (GFCI) sensors are available on some models.
Portable generators are readily available from general rental centers and equipment rental specialists, allowing contractors to limit the number of units owned and rent exactly the models they need for specific projects. Because most rental stores replace equipment on a regular basis, most rental units are relatively new and are equipped with the latest features.
Representatives of generator manufacturers offered these comments about today’s generator projects:
GENERAC POWER SYSTEMS, Dave Rademaker, wholesale channel manager: “We believe electricians want portable generators that have high power output, long run times, multiple receptacles and easy maneuverability of the machine. More and more durability is coming to the forefront. I believe we will see electricians willing to spend the extra dollar for a highly durable portable generator that will save them money in the long run.
“In today’s models, you are seeing higher outputs to run bigger equipment, larger fuel tanks to increase run times and higher durability to avoid the damage that comes with having a generator on a job site. A nice feature on more portable generators is the rugged, all-terrain tires to help with maneuverability in difficult conditions. Another new feature is multiple-voltage output, which facilitates powering welding machines and temporary lighting.
“Battery-powered tools are convenient, but they still have limited operation and recharge needs. And this may have increased the demand for small portable generators, so they can charge tool batteries on the job site while not in use. Higher output generators have their place to supply the high demand of power that batteries simply cannot support. This is the reason 4,000-watt and higher units are being used on a consistent basis.
“To operate computers and office equipment, clean power is a necessity. A portable generator needs a tight voltage and frequency output as well as a long run time,” he said.
GILLETTE GENERATORS, Rodney Weimer, director of sales and marketing: “Electricians need very clean power (total harmonic distortion [THD] of 8 percent or lower), light weight, portability and reliability with a warranty the manufacturer will stand behind. Generators should have OSHA-required GFCI protection on all 120 and 240V AC receptacles, electric start with recoil backup, and fuel tank capacities that provide extended run time.
“There are now portable gas generator sets as large as 22 kW where, two years ago, 15 kW was more or less the maximum size. Physically, the overall size of portable generator sets have been reduced and in some cases enclosed in order to deliver quiet power. Sound levels have been reduced during off-peak performance with auto idle controls, and again, enclosures for portable generator sets have allowed for very low dBA levels.
“Certainly, the equipment is more load sensitive with a cleaner wave form output from the generator. For use with office equipment, THD on the generator end is important—bad THD may cause the computers not to function, flickering or may reduce the overall life of the equipment.
“About half the generators on jobs today are rented. But prices of product from the big box stores are so attractive, or the price of an extended rental users can buy three or four units and throw them away as they fail,” Weimer said.
HONDA POWER EQUIPMENT, Gary Childress, assistant manager, product planning and marketing: “Portable generators today are smaller, more fuel efficient and quieter.
“The development of inverter technology provides equipment offering clean power acceptable for sensitive equipment. This process takes the raw power produced by the generator and passes it through a special microprocessor that provides ultra-clean power with a sine wave equal to or better than AC current from a standard household wall outlet.
“Computers and power-sensitive testing equipment require such clean power—consistent electrical current that has a stable sine wave or signal. A computer without clean power would likely freeze, shut down or its operation be interrupted. Inverter technology also has allowed portable generators to substantially reduce weight and noise.
“When considering your power needs, first determine the highest power application that will be operated by the generator. When operating reactive loads (tools and other devices with electric motors), it requires as much as three times the power to start the device as it does to keep the device running, so 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; loaded power requirements necessary when the tool begins to work—saw begins to cut, drill penetrates material.
“A generator should 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 measure of generator power. Typically, the rated power is 90 percent of maximum power,” Childress said.
WACKER CORP., Marc Leupi, product manager utility: “Electricians require compact, robust generators that can be transported easily and moved around easily once at a job site. GFCI protection is required by OSHA for job sites, so this is a must.
“Power rating categories of popular generator models remain the same as in the past in most cases; however, equipment continues to evolve. One of the most popular features of our generators is the folding lift point, which allows a contractor to lay a board across the top to create a flat working surface, a prized space on any job site.
“A new, state-of-the art alternator, which has a separate excitation winding and soft start [automatic voltage regulator] capability slowly ramps up a heavy load.
“The central GFCI sensor on some models offers full GFCI protection for all outlets, including twist lock outlets. Besides offering the same level of personal protection for all outlets, the system nearly eliminates one of the biggest problems with portable generators: nuisance tripping of outlets with built-in GFCI outlets. By having a stand-alone GFCI sensor that is physically isolated from the main electrical circuit, most nuisance and premature outlet failures are eliminated,” Leupi said.
DEWALT, Tony Nicolaidis, director of marketing, generators: “Our end-user research has found that the most important user requirement for generators is engine reliability. Engine life is critical with a commercial electrician requiring 2,000 hours before any major repair. Stricter engine emission controls as found in California soon will be enforced across the country, and improved emissions at the same time can improve fuel economy, which will be a key consideration.
“Other important features include power output, portability and ease of use. Manufacturers are equipping
electric-start generators with batteries that are smaller and lighter than traditional lead acid batteries. As a result, it is much easier for professional contractors to transport and start portable generators on job sites.
“When evaluating generators, buyers should take into consideration that the generator they want to purchase can handle the load in terms of the amount of power they need. Office items, such as lights and air conditioning systems, use a lot of power, so buyers will want to purchase a generator that is big enough to handle the amount of power they will need,” Nicolaidis said.
KOHLER, Anne Feudner, Kohler rental product manager: “EPA mandates have required changes of emission levels of generators and other equipment. A primary initiative here has been to add fuel capacity to the towable generator fleet. Reducing operating sound levels is another initiative. We also have added GPS technology to portable generators, which enables owners to monitor location, hours of operation and identify service needs.”
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or email@example.com.