Mother Earth News - Mother Earth News 2008

A good electric generator makes your home blackout proof. Its 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?

The first thing to consider is generator output. What size 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 x 120 volts), or the equivalent of a small portable generator. Many people buy a small generator but regret it later because they didnt understand the basic issues. Im one of those people.

The generator Ive used for the last 20 years has a maximum rated output of 3,500 watts. That seemed like enough when I bought it, but its 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), theres 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. For sample wattage data for common appliances, see How Much is Enough?. (Guardian has an online calculator to estimate the size of generator thats best for you. Visit Guardian and click Which One Do I Need?)

Theres also the issue of sustained output. When a manufacturer rates generator output, it usually refers 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, youll 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, Im planning to upgrade to at least a 5,000-watt gasoline generator. Unless you have particularly frugal power requirements, youll find this to be a good basic size. But theres still more to know before you buy.

Any appliance with a motor - a refrigerator, circular saw, drill, water pump or furnace blower - creates whats 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 dont draw significantly more current on start-up. In cases where no wattage consumption figure is stamped on an item, use the volts x amps = watts formula. Youll 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 thats the case, you should consider a stationary generator wired directly into your homes 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.

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. Thats one reason generators typically produce such dirty (irregular) and potentially damaging AC power, filled with lots of high-voltage spikes (see Pure Power below). 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 todays 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. Its a smooth, quiet and economical system thats 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 youll 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.

Regardless of the amount and quality of power you need, theres 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 its 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 algae 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 thats 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.