Application Tips: Generators

The glut in the used generator market is over. Not surprisingly, 2000 and 2001 were horrible years for generator manufacturers. In 1998 and 1999 they couldn’t make enough of the machines to assuage the fears of Y2K doomsayers. But when January 1, 2000, arrived without calamity, people wanted to bring them back. If that didn’t work, they sold them into the used market. The economic downturn that came on the heels of Y2K compounded the situation.

“You had too many units on the ground, too many units in fleets and too many people selling off into the used market,” says John Gibbons, product manager for Terex Light Construction.
But during the past 18 months, almost every generator manufacturer has increased production, he says. The economy has picked back up and rebuilding in Iraq and Afghanistan has pulled equipment, including a large number of generators, out of the U.S. market.

If you are looking to purchase a new generator for the first time in several years, asking yourself the following refresher questions will help you find a unit that fits your applications.

What kind of tools will you be powering with the generator and how many will you use at one time? Once you know how many watts or kilowatts of power you need, you can pick an appropriately sized generator. Remember to consider how much start-up power your tools require. They will typically draw two to five times their running amperage when starting up.

Manufacturers say the most common buying mistake contractors make is not getting the right size generator for their applications. They end up either without enough power or running the generator without enough of a load and wasting fuel. “With fuel prices today, that’s getting to be more and more of a cost,” says Marc Leupi, power product manager for Wacker.

The simple thing to do if you’re worried about not having enough power is to get a much larger generator than you need. The other downside to this – besides the fuel issue – is you can damage a diesel engine if you consistently run it below 50 percent of its capacity. Leupi says a phenomenon called wet stacking occurs. The cylinders collect carbon and the engine’s life is shortened. This is not as much of a problem with gas engines, says Dale Gabrielse, training manager for Robin America, but it can still shorten their lives.

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Where will tools be located in relation to the generator? This will help you decide if you need multiple generators. If you’ll be using tools in areas of your jobsites that are long distances apart, instead of buying one big generator and running extension cords or setting up distribution boxes, you might want to get two smaller generators and position them near the tools, Leupi says.

TIP: Inspect extension and tool cords
everyday. No wires should be exposed.

Do you need three-phase power or just single phase? All generators provide single-phase power. Most mobile, or towable, generators provide single- and three-phase power. Most jobsite tools are single phase, and typically all small handtools in the United States are single phase. But larger equipment and specialty tools (such as tower cranes) that use electric motors are three phase. Large submersible pumps are also three phase.

How durable does the generator need to be? “A jobsite is a very demanding application and there’s lots of potential for impact to the unit,” Leupi says. If you’re buying a portable unit, make sure it has a full frame. Look for a fully enclosed mobile generator. A unit without a lot of air intake openings or air exhaust openings will be less likely to get rain or dirt inside it. Because you’ll probably be pulling it over rough terrain, make sure the generator has a heavy-duty trailer.

How important is frequency regulation? If you will be using tools or equipment with electronics, especially computers or electronic measuring equipment, they will be sensitive to frequency fluctuations. Generator manufacturers recommend you buy a unit with an electronic governor. This will give you precise frequency regulation – within 0.1 hertz of the 60-hertz U.S. standard.

With a mechanical governor, frequency can range as much as 5 percent, damaging electronic components. “More and more tools have electronics built into them,” Leupi says.

“You have to consider this as soon as you get into anything more sophisticated than a hand tool – breakers, for example, have more sophisticated electronics that allow them to perform better -but you also need a cleaner electrical supply.” Some tools have solid-state circuit protection that won’t allow them to run if frequency or voltage isn’t within a preset range.

Are there noise restrictions at your jobsites? If so, you might need to buy a sound-attenuated model. Most units have decibel ratings in the mid 60s to low 70s, with the average being about 68. “Some generators are extremely quiet, some are very loud, and a lot of them are in between,” says John Leisner, product manager for Miller Electric. Local noise ordinances vary considerably, but less than 68 decibels is usually acceptable, Raber says. It also helps to know if noise won’t be a factor. If you’re working on jobsites such as big road projects in rural areas you can save yourself about 20 percent the cost of the generator by buying a unit that isn’t extra-quiet.

TIP: Know how many tools you want to power at one time and their wattage requirements before you purchase a generator. Don’t forget the amount of power a tool needs at startup is usually two to five times as much as it requires to run.

How hot do your jobsites get? Generators are set to run at a certain ambience, typically 95, 100 or 105 degrees. If the temperature is consistently warmer than that and you are running the generator at its capacity, it will begin to bog down and you’ll have to take some of the load off. If you know you need a 40-kilowatt generator in Phoenix, for instance, you would probably be better off buying a 60-kilowatt model because there’s not a big price difference.

Do you want to be able to check for phase imbalances? Gibbons recommends buying a generator that gives you this capability. If you have a three-phase generator and it’s running one leg at 90 percent, one at 70 percent and another at 20 percent, the one at 90 percent is working harder and getting hotter. Heat is what kills a generator eventually. Electricity makes heat that breaks down the windings and ends the life of the generator after several thousand hours. “If you want to make it last as long as possible, you want to know you’ve got your load balanced,” Gibbons says. To do this, you’ll need an electronic gauge readout or a phase selector switch.