Guide to selecting a portable generator

The key to selecting the best portable generator is to consider how much power you need for the jobs you do and which features will work best for you.

Portable generators are available in a variety of styles, wattages and prices. For contractors, the key to selecting a portable generator is to consider how much power you need for the jobs you do and which features will work best for you.

Generators produce power in direct proportion to the engine’s horsepower rating – the more horsepower, the more wattage the generator produces.

Generators typically carry two ratings: maximum and rated, with the rated power usually being about 90 percent of the maximum rating. Generators should not be operated at maximum power for more than 20 or 30 minutes at a time. Rated power is the output a generator can safely produce for extended periods of time, so base your selection on that number.

For selecting a portable generator and to know how much power you’ll need, determine the power draw of the power tools you’ll be using for the job and how many power tools you’ll be using at one time. A simple example: A generator with a maximum rating of 10,000 watts can power 100 100-watt light bulbs simultaneously for about 30 minutes. The rated wattage would be about 9,000 watts, meaning it could power 90 100-watt bulbs at one time all night long.

Once you know the power rating you need, determine what features you need using these questions.

Determine how often you’ll be moving the generator, which handle and wheel style will allow you to move it easily and comfortably on your typical jobsites, and how you’ll transport it.

How will the portable generator be transported?

Most smaller, albeit less powerful, generators are easily transported by one person – even up and down stairs. Larger, more powerful units can be transported using wheels and handles. The heaviest units feature steel carrying hooks integrated into the frame so they can be moved by construction equipment.

Determine how often you’ll be moving the generator, which handle and wheel style will allow you to move it easily and comfortably on your typical jobsites, and how you’ll transport it.

How quiet should it be?

If the generator will be used in semi-enclosed spaces or in close proximity to workers for extended periods of time, compare the decibel ratings for the models you are considering and choose a quieter model.

Before you pick a generator determine which features you need and which are likely to go unused.

Which features do you actually need?

The features available on generator vary. Before selecting a portable generator determine which features you need and which are likely to go unused. Here are some typical generator features:

• GFCI outlets are not standard on all generators, but they are a must if working with tools outside or near water.
• Low-oil shutoffs prevent a generator’s motor from burning out from low oil levels. They are a must if you are working away from the generator or unable to monitor it throughout the day.
• Electric start may not seem like a necessity, but you might wish you had it after pulling on a recoil rope a few dozen times on a cold morning.
• Power gauges can prevent you from tripping a circuit, forcing you to stop work and reset it. Tripping a circuit can damage the tools you are using.
• With an “idle-down” feature, the generator automatically idles the engine when power is not required, increasing engine and alternator live, increasing overall runtime, and reducing noise.
• Larger generators have larger fuel tanks, which means you can keep working longer. For example, a 6-gallon fuel tank on a gasoline model should provide steady power for up to 12½ hours at 50 percent load.
• You’ll likely want to purchase a generator that uses the fuel type you use most often on your jobsites, i.e. if you’re set up to refuel with gasoline, but not diesel fuel, you’ll probably want a gas-powered machine.

Portable generator styles

Light-duty: These low-power units range from 1,000 to 5,500 watts and are easy to move on a jobsite to power a paint sprayer or a pancake compressor. Most light-duty compressors are gas-powered.

Utility or emergency:  With wattage ranging from 1,200 to 17,500, this type of portable generator is often used for emergency standby power. Power choices are gas, LP and natural gas. The smaller gas versions are an economical choice for contractors who don’t often need jobsite power.

Semi-professional: A good choice for most residential contractors, semi-professional units are usually gas powered. More portable than most professional models, these generators typically have fewer features – and cost less. Wattage ranges from 3,500 to 10,000.

Professional: Heavy-duty professional-quality portable generators are designed to be used daily. They are usually less portable, although manufacturers are always working to make them easier to move, and more durable and they are the most expensive. Professional generators deliver 2,500 to 15,000 watts and are gasoline or diesel powered.