Portable power

Performance, reliability and durability make jobsite generators stand out from the rest.

Jobsite generator experts agree: When it comes to selecting a generator, you get what you pay for. If you take a shortcut on features, you will be shortchanged on performance, reliability and durability.

“The biggest error made in choosing a generator is buying a unit that is too small. You can never have too many watts when it comes to generators on jobsites,” says Charles Hampton, generator product manager at Porter-Cable. “Buy the largest unit that still offers the portability required by your work.”

“Contractors want performance, reliability and durability,” says Pete Morris, DeWalt generator product manager. New models offer advanced features that help the units meet jobsite demands.

It starts with the engine
The experts agree the generator’s engine plays an important role in determining the overall quality of the unit. “When it comes to reliability, it’s almost always engine-related,” says Morris. “If the engine doesn’t have the torque to get the generator through a sustained load, voltage will drop,” he says.

The engine is also the most expensive generator component. Jobsite-quality generators have overhead valve engines built to take extended run times. “Side valve engines can’t take the long run times contractors need. Overhead valve engines also run quieter,” says Hampton.

“The engine should have ball bearing construction supporting the crankshaft vs. a bushing type of shaft support. The engine’s block should be made out of an aluminum alloy material cast under high pressure for long life. These materials wear better, have tighter tolerances and dissipate heat better than engines made with low-pressure cast blocks,” says Colin Iwasa, generator marketing, product planning and sales at Yamaha. “Look at the muffler used on the unit. It should be oversized to minimize noise levels,” he adds.

Finally, the experts agree the gas tank should be big enough to run all day without refueling.

Generator design
Most jobsite generators provide 120/240-volt power. “The generator has two sets of windings, each set powering one circuit for 120-volt power,” says Hampton. A central tap neutral pulls power from both windings to produce 240-volt power.

Most all jobsite generators have a “full power” switch that allows the generator to use both sets of windings to produce 120 volt power, giving the unit more capacity to handle heavy loads. However, few contractors understand how it works.

“On jobsites I have visited, about half of the full power switches were set correctly,” says Morris. This switch allows the generator to fully use its windings to start heavy loads.

“With the full power switch in the right position, you get twice the surge capability for starting heavy loads such as compressors,” says Hampton.

Another way to maximize the generator’s output capability is to use all of the duplex receptacles on the generator. “Instead of plugging one extension cord into the generator and branching off of it inside the building, run an extension cord from each receptacle. Each duplex receptacle is wired as a separate circuit. That gives you full capacity from the generator windings instead to pulling all of the current from one side of the generator,” says Morris.

Another option: Use a power box that pulls power from the 240-volt receptacle and break it into two circuits of 120-volt power. This allows you to use heavier wiring to get the power into the building, then branch it from there to run tools.

Generators are commonly outfitted with two types of circuit breakers for user and generator safety. The first line of defense is a thermally activated circuit breaker that will protect the unit from overheating. The second breaker is electromagnetically-
driven and protects the generator and the worker from short circuits.

OSHA requires that ground-fault circuit interrupt (GFCI) protection be used on any 120-volt, 15- or 20-amp receptacle used on jobsites.

However, it is not required as standard equipment on generators smaller than 5,000 watts, although many manufacturers include them. If the generator does not have GFCI protection, it should be provided through a GFCI-equipped extension cord.

Built to take a beating
Generators are subjected to unintentional abuse. “They can slide around in back of pickups which can damage components,” says Morris. For transport, the units should be tied down with straps.

Today’s models incorporate roll cage protection into the generator frame, wrapping around the engine, fuel tank, generator and control panel to protect it from jobsite impacts. Rocker switches are more damage-resistant than toggle switches.

“Look for flush-mounted components that don’t stick out from the unit,” says Hampton.

Morris suggests you consider how you plan to transport the generator on the jobsite. “Many contractors choose not to buy a wheel kit when they first buy the unit, then regret not getting it. It’s easier to put on before you put the generator into service and makes it more portable,” he says.

He also suggests looking at the unit’s wheels. Narrow wheels can sink in mud; pneumatic wheels can go flat from punctures. “Wide, semi-pneumatic wheels can handle jobsite terrain,” he says.

New generation generators
New generator models sport many user-friendly features that protect the units and make them easier to use, but they are variations on the same old theme: an engine that’s capable of turning the generator at 3,600 rpm to produce 60 Hz power.

Yamaha recently introduced a solid-state generator that is lighter, more fuel-efficient and even more reliable. Other generator manufacturers are also researching this technology.

“These generators use inverter technology to provide power,” says Iwasa. The units weigh 30 percent less than a conventional unit with similar output.

“The inverter allows the engine to match the power to demand. Conventional units need the engine to turn the generator at 3,600 rpm to get the 60 Hz power. With an inverter, the engine only runs as hard as it needs to produce the power required,” Iwasa explains. “The units burn less fuel and run quieter. They are smaller and lighter, so one person can easily move them. Contractors testing the units like them. They cost about the same as conventional units of similar output.”

Published in the January/February, 2002 issue of Contractor Tools and Supplies magazine.

back to top