Choosing the Right Generator
By Steve Maxwell | Nov 28, 2008
Generator Oil Treatment
Two Types of Power
Wattage Per Household Appliance
Keeping Fuel Fresh
Four Generator Safety Tips
Most of us live just one blackout away from the Stone Age, but this fact is easy to forget until the lights go out. A good electric generator makes your home blackout proof. It’s relatively inexpensive insurance against complete loss of household power. Plus, portable units are convenient when you need electricity beyond the reach of an extension cord.
All generators combine an internal combustion engine with electrical components to create electricity for powering appliances and tools. Choosing a generator involves several key decisions. How much power do you really need? How often do you expect to use it? Will it be for emergency household backup? For tools? Both? What level of quality makes sense? What kind of fuel? How will you get the power from the generator to items in your home?
More power to you
The first thing to consider is generator output – determining the size that is right for your situation. This sounds simpler than it really is because not all items on your wish list are going to be used all the time or at the same time. Also, some appliances (such as furnace fans, sump pumps, washing machines and refrigerators) require more start-up power than their specified ratings.
Generator output is measured in watts, a unit of power derived by multiplying electrical flow rate (amps) by electrical pressure (volts). One typical household outlet, for example, delivers a maximum of 1,800 watts (15 amps multiplied by 120 volts), or the equivalent of a small portable generator. Many people buy a small generator but regret it later because they didn’t understand the basic issues. I’m one of those people.
The generator I’ve used for the last 20 years has a maximum rated output of 3,500 watts. That seemed like enough when I bought it, but it’s proven barely adequate for emergency backup. By the time the submersible well pump kicks in (1,500 watts at start-up), the basement freezer is running (800 watts) and a few lights are on (100 watts for several compact fluorescents), there’s not much power left for other things. If we want to use the microwave or toaster oven, we have to make sure that most other items are switched off. There’s also the issue of sustained output. When manufacturers rate generator output, they usually refer to a maximum, short-term level only. In practice, most generators can sustain only 80 percent of their maximum rating for the long haul. If you continuously demand more than this, you’ll shorten the life of your investment. Unless stated otherwise, always consider advertised generator output as overly optimistic and apply the 80 percent rule.
Because of the reasons listed above, I’m planning to upgrade to at least a 5,000-watt gasoline generator. Unless you have particularly frugal power requirements, you’ll find this to be a good basic size. But there’s still more to know before you buy.
Watt’s up with start-up?
Any appliance with a motor – a refrigerator, circular saw, drill, water pump or furnace blower – creates what’s called an “inductive” electrical load. This means energy demand skyrockets for the first second or two after start-up. You should allow two or three times as many watts for start-up compared to watts required while running. Heating elements (in stoves, toasters or space heaters), lights and small motors don’t draw significantly more current on start-up. In cases where no wattage consumption figure is stamped on an item, use the formula: volts x amps = watts. You’ll almost certainly find volt and amp numbers stamped somewhere on an appliance.
As you do the math, you may discover that you want more than 5,000 watts of backup power. If that’s the case, you should consider a stationary generator wired directly into your home’s electrical system. These units are covered by weatherproof shrouds and are ready to kick in either manually or automatically whenever the power goes off. Stationary units cost more than portables, but they deliver more power. Prices for units large enough to run multiple appliances and lights during a blackout range from about $3,000 to more than $10,000.
A dirty little secret
The quality of power is important, too. Most generators create a specific frequency of alternating current (AC) by precisely governing motor speed – or at least they try to. But in reality, governor engine control is mechanical and pretty crude, especially on cheaper generators. That’s one reason generators typically produce such dirty (irregular) and potentially damaging AC power, filled with lots of high-voltage spikes (see “Two Types of Power”). But the latest generation of “clean power” generators, often called inverters, takes a different approach.
These generators have a fuel economy feature that tailors engine output speed to electrical load demanded. Traditional generators run full blast, regardless of how much power you need. The engines on today’s best generators run only as fast as needed to create the power required. Switch on a light bulb, for instance, and the motor speeds up slightly from an idle. Plug in a 1,500-watt hot plate, and motor speed increases further to meet the electrical demand. It’s a smooth, quiet and economical system that’s easier on the environment. It also significantly reduces noise output.
At the other end of the spectrum are less expensive generators with basic engines, no-frills electronics and less than optimal mufflers. These are worth consideration if you’ll only be powering large, simple electrical items such as cooking appliances, water pumps or basic power tools.
So how do you tell the difference between premium-quality and economy generators? Engine design is one way. The most durable generator engines have overhead valves and commercial-duty chrome or cast-iron cylinder sleeves. Economy models have side valves and aluminum cylinders.
Prices reflect quality, too; top-of-the-line generators cost about two or three times as much as economy models for a given wattage output.
The right fuel
Regardless of the amount and quality of power you need, there’s also the question of fuel type. Most portable generators run on gasoline, but there are advantages to propane- and diesel-fueled models, too.
Propane (also called liquefied petroleum gas or LPG) is more expensive than other fuel options when you buy it in small tanks like those used with an outdoor grill. But it’s also more chemically stable than gasoline or diesel. Ordinary gasoline becomes significantly less flammable after several months of storage as key chemicals break down or evaporate. Diesel fuel also is susceptible to degradation by fungal growth. You can expect two years of reliable shelf life by adding a conditioner to gas or diesel fuel, but LPG never goes stale, so an LPG system is worth considering if your generator will be used for emergency backup only. But, understand that what you gain in fuel stability, you lose in generator portability.
Diesel engines are traditionally found only on large, stationary generators, but that’s starting to change. Smaller diesel systems in the 4,000-watt range are now appearing on the market. Diesel engines are harder to start and usually cost more than comparable gasoline motors, but they last longer, especially for continuous use.
Got a tractor? A whole range of PTO-powered (Power Take Off) generators are available, most for medium and large power output. These units aren’t usually designed to put out the kind of clean (regular) power required by sensitive home electronics. Generator systems also can be installed onto engines in cars and trucks, either under the hood or attached to a PTO. It’s not always a simple installation, but it does offer relatively large power output, quiet operation and portability.
You can get power from your generator to the place you need it in two ways. Extension cords are easy to use, but limited. You have to run them from outside to indoors, and even then you can only energize items that have a plug-in cord. But if you have a generator that puts out 3,500 watts or more, it’s worth creating a connection directly to your household wiring so nearly everything requiring electricity in your home can be used (at least in theory). But there’s a catch: To be safe and legal, any such direct connection must pass through a transfer switch. This safety device ensures that either your home is connected to the grid or to your generator, but never to both at the same time.
Installing a transfer switch involves splicing into the main cables feeding your house and is a mandatory safety precaution to protect utility workers. If your generator happens to be feeding power into your home while your main breaker is still switched on, it will deliver unexpected, phantom power to the utility lines. Work crews might have switched off incoming power to your area to complete work safely, but power from your generator would be hitting them from behind. For more safety tips, see “Four Generator Safety Tips.”
We’ve all seen how vulnerable the electrical grid is to major weather events and overloads, and that’s the reason I like the security offered by a backup generator. Choose your equipment well, keep it in good shape, and it will provide peace of mind that you simply can’t get in any other way.
Steve Maxwell has had some shocking experiences with generators. He’s been a hard-core do-it-yourselfer, builder and writer for more than 20 years. This article was originally published in Mother Earth News (www.MotherEarthNews.com).
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