Clean power

Quiet-running and fuel-stingy, inverter generators can provide the clean power needed by jobsite computers and electronically controlled smart tools.

Most of the time, contractors are just happy to have access to an extension cord that’s properly grounded and GFCI-protected on the jobsite.

But with the increasing use of personal computers, microprocessor-controlled tools and Internet connections at the very start of projects, the demand for clean, reliable jobsite power has reached new heights even before power reaches the jobsite.

That’s where inverter-type generators are gaining favor. They are the darlings of the recreational vehicle market because they can produce clean power with low noise levels and better fuel efficiency, and are turning heads on jobsites for the very same reasons, cite generator experts.

“Sine” of the times
You may need to brush off your tech-ed textbook and read up on the chapter about alternating current (AC) power to understand what makes an inverter generator different from a conventional generator.

AC power forms a sine wave on an oscilloscope, which means that the positive and negative charge alternates. In the case of common utility-supplied power, it does this at 60 Hz or cycles per second.

“That’s the type of power that conventional generators produce,” says Pam Meyer, equipment sales manager at Subaru Robin. “However, it’s considered dirty power because the sine wave will appear jagged if it’s measured on an oscilloscope. Those small spikes in the sine wave indicate noise or resistance that can cause lights to flicker and cause problems for tools and appliances that need a clean sine wave to operate. Computers and tools such as some rotary hammers with smart chips to control speed under varying loads won’t operate well with dirty power.”

“Inverter technology provides ultra-clean power that boasts a sine wave equal to or better than the current from your household AC wall outlet,” adds Scott Podella with Briggs & Stratton Power Products Group. “The inverter generates power at a much lower voltage than 120 volts (usually 12 volts to 36 volts) and then ‘inverts’ it electronically to 120 volts AC power.”

The units also run quieter, adds Meyer. “Inverter generators run about 10 dB(a) quieter than conventional units. For example, our RG3200iS unit operates at about 58 dB(a); a vacuum cleaner creates sound levels of around 70 dB(a).”

Colin Iwasa, marketing and product planning manager at Yamaha, concurs. “Conventional generators are the old, reliable design that we’re all accustomed to seeing. They take electricity that is produced directly from an armature passing though a magnetic field produced by a coil. The quality of the electricity is determined by the quality of the engine, how smoothly it runs and how well the engine is capable of maintaining a constant speed. The quality of the magnetic field, which depends upon the quality of the windings, also affects power quality,” he says.
The inverter generator converts the power coming out of the armature coil from AC power to direct current (DC) power, then inverts it back to AC power through an electronic filter, often called a black box. “This design costs more than a conventional generator, but has many benefits,” Iwasa says.

Watt for watt, an inverter generator weighs less and is smaller in size than its conventional generator cousin.

Inverter generators also have the ability to vary engine speed to match the power requirement, while conventional generators must maintain a set speed to produce 60 Hz power. “This reduces noise, fuel consumption and engine wear when compared with conventional generators,” says Iwasa.

Black box technology
A contractor could run power produced from a conventional generator through a low-cost inverter, but may not achieve the same power quality that the inverter generators produce, adds Iwasa.

Meyer says the Subaru Robin inverter generators create more than 300 sine waves per rotation, which amounts to more electrical power produced per rotation. Then, the inverter takes that power and converts it first to DC power, then takes the next step to electronically convert it to very clean 120 volt, 60 Hz AC power.

Iwasa says that Yamaha’s inverter generators use Yamaha’s Pulse Width Modulation inverters to produce a pure sine wave that can run sensitive electronic equipment. “These units can be used anywhere a conventional generator can be used, but neither type should be used in enclosed spaces or run anywhere that would allow the exhaust to enter living or working space or be used to power life-
support equipment,” he says.

Motor starting tips
Although the power is cleaner from inverter generators, the units must still be right-sized for the job. That means totaling your expected loads and selecting the right generator for the job.

“Starting an electric motor requires up to three times more power than it takes to make it run. Check the power requirements on the tool’s identification tag to find its running power need, then triple it for the power needed for motor starting,” Iwasa says.

For other tools and appliances, Iwasa suggests looking at the wattage each electrical tool or appliance requires to operate.

If only amps are listed on the tool, multiply the amp rating with the voltage to calculate the tool’s watt rating.

You get what you pay for
Iwasa and Meyer say that price is a generally good indicator of generator quality. Better-built units will have better warranties, more resilient components and features that help protect the unit from overheating.

Published in the July/August 2006 issue of Contractor Tools and Supplies magazine.

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