How Do I Choose a Generator?

By CTD Blogger published on in Consumer Information

For a preparedness-minded individual, it is easy to see the value of owning a generator. Actually choosing the type and size of generator to buy can be quite intimidating. Generators are application-specific tools, meaning the right generator will vary depending on its intended use. The most common generators people think of are 10,000-watt portable gasoline generators, and there are many more that fit a variety of situations.

Generator Type

Small Generator for Home Use

Understanding the types of generators is a first step to deciding which one is right for you.

Portable

Portable generators are by far the most common generators, ranging from 1,000 watts to 80,000-watt trailer mounted sets. The most common sizes are 3,000 to 10,000 watt gasoline-powered generators.

  • The smaller economy-model generators are little more than a lawn mower engine attached to a dynamo. They have aluminum sleeves, use side valves and are not manufactured for extended use. They often have minimal electronics, and the power they generate can be very “dirty.”
  • Larger commercial generators use overhead valves and steel sleeves and are often computer-controlled so the power produced is clean and consistent. The engine runs at maximum efficiency, regardless of the load.

Fixed

Commonly found at data centers, hospitals, prisons and other locations needing uninterrupted power, fixed generators are large systems and are not designed to be moved once installed. They are generally hardwired to the building and set up to automatically provide power once grid power has been down for a predetermined amount of time.

Power Take Off (PTO)

A less common type of generator is the Power Take Off, or PTO, generator. The alternator in your car is actually a small PTO generator, although it does not power much. Most PTO generators are mounted onto the main PTO of a tractor or to some vehicle transmissions. They are also available as just a plain PTO you could, theoretically, mount on any rotating drive shaft.

Industrial and Turbine

These generators are truly massive beasts. Often generating in excess of 250,000 watts. They are usually only found at large outdoor concerts, traveling carnivals or permanently installed in large commercial installations. Turbines have the advantage of being relatively quiet compared to piston-driven generators.

Portable versions of the huge behemoths are either mounted on 18-wheeler trailers or have a trailer integrated into the generator itself. It’s unlikely a single individual would ever need such a large generator. They are often trucked in for use by first responders when power is knocked out to entire cities for weeks at a time, such as in the aftermath of a hurricane or earthquake.

Fuel Type

One very important concern when choosing a generator is the type of fuel it uses.

Propane

Most residential backup generators use propane and natural gas interchangeably. Liquid propane is easy to store and, in rural areas, large storage tanks are commonly found at every house and business and propane delivery services are widely available to keep these tanks full. In urban settings, large tanks are less common and more heavily regulated, though small versions are very common due to their prevalent use in starting BBQ grills and other outdoor accessories.

Natural Gas

Most homes in the United States have access to natural gas through municipal gas lines, which makes it very convenient when you install a residential backup generator. Be aware that in certain situations, if the local power grid goes down, it is likely that municipal gas lines may lose pressure and go down as well. Be sure to have an alternate fuel source, such as propane, available.

Diesel

While diesel does not go bad as quickly as gasoline, it is still susceptible to hydration and fungal growth if not treated with an additive. Diesel has the advantage of being easier to store and it is a more efficient fuel. Diesel-powered generators usually need less maintenance and have a longer operational lifespan. While not common yet, a few small portable diesel-powered generators are available.

Gasoline

Gasoline is the most common fuel used for small portable generators rated for less than 20,000 watts. Gasoline-powered generators require the most maintenance and have the shortest lifespan of any fuel type. Storing gasoline is a problem since it decays within just a few weeks unless stabilized with additives. Even with the use of stabilizing agents, it is generally not a good idea to use gasoline stored longer than two years.

Gasoline is the most dangerous fuel to store, due to its low flash point (the point at which fuel fumes form an ignitable mixture in the air) and its sensitivity to temperature fluctuations.

Power

Even though you need a generator to produce power, you also need to understand how to power the generator.

Understanding Ratings and Choosing the Right Size

All generators are rated for two wattages. There is a big difference between a generators’ peak capacity, or surge wattage, and its rated operating capacity. Most generators are designed to run at approximately 75% of its surge watt rating. If you run at more than 75% capacity for a long period of time, the generator undergoes excessive wear and tear and eventually becomes damaged. Exceeding the surge watt rating for even a limited amount of time can damage or destroy a generator.

Knowing what your energy demands are helps you choose a properly-sized generator. If you have a refrigerator (3,000 watt start up), a hot water heater (3,000 watts), and a well pump (1,500 watt start up) you need to run, you have a total energy demand of 6,500 watts. Given that demand, you need a generator with a surge rating of at least 9,000 watts. This leaves you 250 watts to power some lights while keeping you within the 75% total load guideline.

A recommended rule of thumb is to calculate your total need, add in the overhead so your load is 75% of the rating, and then double that. That means that instead of a 9,000 watt we would buy an 18,000 watt generator to allow for future energy needs.

Start-up Load v. Running Load

Many appliances have a very high inductive start-up load. The start-up load is the power it takes to get an electric motor moving. All electric motors draw the most power and produce the most torque while starting up. These loads are often 2-3 times higher than the operating load. Naturally, this puts a higher demand on the generator so be sure to consider start-up loads when calculating the total load demanded of the generator.

Power Quality

Power quality used to be a concern with older generators since they attempted to create a specific frequency (usually 110v – 120v at 60 hertz) of AC current by governing engine speed. This mechanical means of regulation was not perfect, and the result was fluctuations in the frequency and voltage, or “dirty” power. Dirty power isn’t an issue with light bulbs, heating elements, or most motor-driven appliances, but it can play hell with computers and computer-controlled appliances, as well as some transformer-powered appliances.

Small economy style generators still produce “dirty” power, although most modern generators have computer-controlled power outputs and have no problem putting out perfect sine-wave 60 hertz AC power.

Wiring Concerns

Having a generator is great, but how do you get the electrical power to where you need it? Extension cords are a natural solution although are limited in their usefulness. A typical household outlet is capable of running 1,500 to 2,000 watts of continuous power. A single extension cord should never be used to supply more than 1,800 watts (approximately 15 amps) of power. If you need an extension cord run of 50–100 feet, make sure to use a 12 gauge cord and remain within the 1,800 watt guideline.

For large generators (3,500 watts or more) it makes more sense to install a transfer switch that allows the generator to supply power directly to the house wiring. Transfer switches isolate the house wiring and generator from the grid. If the house were not isolated, the generator would be putting power down the power lines at potentially deadly voltages. This would obviously endanger repair crews and potentially damage the generator.

Choosing the Right Size Generator

Average Power Demands of Common Appliances

Appliance Start-up Watts Operating Watts
Furnace fan 1,400 700
Portable Heater 1,800 1,500
Well pump (½-horsepower) 1,500 750
Sump Pump 3200 1700
Refrigerator 1,500 800
40-gallon water heater 3,000 3,000
Freezer 2,000 800
Refrigerator 3,000 1,200
Water Heater 4,000 4,000
Clothes Washer 1,500 750
Light Bulb 60 60
Home Security Alarm 100 100
VCR 50 50
Radio 100 100
TV/Computer 350 350
Microwave 750 750
Coffee maker 850 850
Electric Skillet 1,200 1,200
Crock pot 250 250
2-slice toaster 1,100 1,100
Plug-in heater 1,500 1,500
7¼-inch circular saw 1,500 750
Belt Sander 1,900 1,500
Bench Grinder 1,800 700
Jig Saw 900 600
3/8-inch Hand Drill 750 500

 

Safety Concerns

Making sure you, your family AND your equipment are safe is a top priority when choosing a generator.

Fuel Storage

If you’ve got a generator you’re going to need fuel for it. In a situation where the power is out, most fuel stations are unable to pump fuel. This means that you’re going to have a fuel storage system.

  • Store fuel in a detached structure away from a house or living quarters.
  • Always abide by local fire codes and safe storage laws.
  • Even stored in a proper container, gasoline should never be stored in a building with any pilot lights or open flames.
  • Rotate stored gasoline and diesel out on a yearly basis and restock with fresh fuel.

Exhaust

  • Always run generators in a well-ventilated area with the exhaust away from people.
  • Never run a portable generator indoors or in an enclosed porch or garage.
  • Install a carbon monoxide detector in your living area to detect any dangerous fumes in the house.

Grounding and Electrical Safety

When running the wiring for your generator, don’t neglect grounding requirements.

  • If possible, the frame of your generator should be bonded to your house ground.
  • If you are using an extension cord and not bonding to your house, then you can achieve adequate grounding by driving a 12” metal stake into the ground and wiring that to the generator frame.

Generator Maintenance

Make sure you carefully maintain your generator so it is ready if, or when, you need it.

Storage

If you are using a gasoline powered generator, do not store it with fuel in the tank. When preparing the generator for storage:

  1. Drain the fuel tank
  2. Run the generator until the fuel line and carburetor are dry. This prevents gummy deposits forming from fuel left in the system.

Like most small engines, run your generator with a load at least twice a year and check and clean sparkplugs once a year.

Oil Changes

Check your owner’s manual for the recommended service intervals for your specific generator. Be aware that some smaller, economy model generators require oil changes as frequently as every 24 hours of use. This means that you should always have a ready supply of oil on hand for your generator so you can change the oil during a power outage.

Parts Compatibility

Some generators use common automobile based parts, such as spin-on oil filters, and commonly found fuel and air filters. When purchasing a generator, find out if parts that wear out are easily replaced. A generator with a bad spark plug is useless if you cannot easily find a replacement. Use particular caution when considering generators from smaller companies, as these often have parts that are difficult to find replacements for if they break.

Do you have a generator on hand? Have you had to use it? Share your experiences in the comment section.

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The mission of Cheaper Than Dirt!'s blog, "The Shooter's Log," is to provide information-not opinions-to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (3)

  • Mandy

    |

    This guide is quite informative. Thank you for this. I was in the market of buying a generator because we’ve been experiencing black outs frequently due to low water reserves on our local dam.

    Reply

  • Lillian Schaeffer

    |

    This is some great information, and I appreciate your suggestion to choose a generator that can fulfill your needs while only hitting 75% of its surge watt rating. My husband and I have been discussing ways to become more prepared for emergencies, and one thing we’ve talked about is power outages. We’ve decided to get a generator, so we’ll make sure to get one that can cover all of our electric needs while only at 75% capacity so it doesn’t get worn out. Thanks for the great post!

    Reply

  • TexasScout

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    One thing about fuel. The best “Long term” fuel to store I’d propane. It just never goes bad. Gasoline and diesel will both go ban within 5-7 years. Propane will last as long as it doesn’t leak. Only Kerosene comes lasts longer than other liquid fuels, but not by much.

    There is also the benefit of not filling your carbarator bowl with varnish after sitting for a couple of years.

    Tex

    Reply

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