Generator Buying Guide
The generator buying guide for the smart buyer.
When it comes to purchasing a generator, you want to be an informed buyer! To make the right choice, you should be familiar with a few electronic terms and have a basic understanding of the different types of power generators and their operating principles.
To select the generator that will meet your power needs you must first "size" your electric generator by determining how many watts you will require to operate all your essential equipment. Choosing the correct wattage is critical as too few watts can overwork the electric generator, potentially damaging it and anything plugged into it, while too many will waste your money on the initial generator purchase and on the fuel required to run it.
The electricity created by a power generator is measured terms of voltage and watts. When choosing a power generator, you'll need to know the specific voltage your situation requires, and then pick the model that supplies enough wattage to cover all the equipment you'll be running. Unlike voltage requirements, which are set based on your existing circuits and electric service (i.e. 120/240volts service or 120/208 volts or 277/480 volts service), wattage requirements increase with each additional appliance you want the generator to power. The smallest generators produce around 800 watts, while large industrial generators can produce 500,000 watts (500 kilowatts, or kW) or more. Typical sizes for small businesses are around 15 to 100 kW.
Remember that during power outages the main concern is for powering sufficiently for the safety of your family. If power is out for several hours you will want to ensure adequate heat and lighting and power the refrigerator and freezer to avoid food spoilage. It is important to note that it is not necessary to continually power these appliances: if your generator has a small power output, power management will allow you to utilize a small generator to power several appliances safely. In general, since most home appliances operate intermittently, a 3000-watt generator can provide adequate power for the most common appliances such as a furnace, lights, refrigerator, freezer, microwave, and TV. If your home has a deep well pump with up to 1 HP motor, a 5000-watt generator will be required to provide the starting capacity for the pump.
Be familiar with "maximum power theory" of electric generators (and motors as well). An electric generator can deliver its maximum capacity for no more than 30 minutes before starting to overheat. Therefore, don't push it to the max! Rather, in generator jargon, "Rated Power" is the operative word, and refers to the power that a generator can produce for long periods of time, which is a more reliable measure of generator power. Typically the RATED power is 90% of the MAXIMUM power. It has been further recommended that you purchase a generator with a rated capacity of around 20% more than your exact requirements to avoid overworking your generator. This will allow you to add a few small devices and help extend the lifespan of the generator.
Finally, equip yourself with this next item of generator know-how: Running Wattage vs. Surge or Start Wattage. Run wattage is the amount of electricity necessary to run an appliance, while surge wattage is a higher amount of electricity necessary to start (2-3 seconds) electric motors commonly found in household appliances such as a furnace or refrigerator.
Since appliances rarely start up at the same time, you will only need to factor in the surge wattage with the largest difference between running watts and surge watts. For example, if you require 6,000 running watts and the appliance with the greatest difference between running watts and surge watts has a difference of 2,000, the generator you select will need to be able to accommodate up to 8,000 surge watts - 6,000 (run watts) + 2,000 (greatest difference between run and surge watts) = 8,000 (surge watts).
The following power requirement chart may help you determine your power wattage needs. Note that on the back of each appliance there is usually a UL tag that indicates its starting wattage. Remember: the more appliances you add, the more you will pay for your generator!
Gas or Diesel?
Generators can run on several different types of fuel. Diesel electric generators are popular for larger, commercial applications due to their longevity and lower operating costs. Today's modern diesels are quiet and normally require much less maintenance than comparably sized gas (natural gas or propane) electric generators. Fuel costs per kW produced with diesels is normally thirty to fifty percent less than gas units. However, they do require deliveries of diesel fuel and a tank to hold it, and while they've cleaned up their act considerably in recent years, diesel generators are still not as clean-burning as other types.
Standby generators can run on natural gas or propane. The primary advantage is that no fuel storage is required - the generator is simply connected to utility lines and draws fuel when it needs to. The choice between gas and propane is based solely on which is available in your area.
For portable generators, the most common choice for fuel is gasoline. The only drawback is that gasoline cannot be stored for long, so if you intend to keep a portable generator around for emergencies, you may want to consider propane instead. Whichever fuel you choose, ensure that the fuel tank is large enough to give you an appropriate amount of running time, and look for a fuel indicator gauge - knowing how much gas is left in the tank can give you important peace of mind. Both portable and standby generators are sometimes available in dual- or tri-fuel configurations, where switching from natural gas to gasoline to propane is made simple.
* Quality standby generators will include safety features, i.e. shut down if they lose oil pressure, overheat, or are being worked too hard.
* Standby generators should have solid steel or aluminum enclosures, good mufflers to reduce noise, and be compliant with all relevant emissions regulations.
* Remember to include all you need - some of the more important devices to connect to a standby generator are some of the least visible: sump pumps, sewage ejector pumps, and ventilation fans.
Portable generators should have large fuel tanks for the best running time, a fuel indicator gauge, and enough receptacles to allow you to plug in all the devices you want to run.
Summary: Questions You Should Ask Before You Buy a Generator
What is the generator's wattage capacity and will it support your needs, including startup surge power required by some equipment?
Does the generator have enough outlets to plug in all of the items you want to power?
How noisy is the generator? Are there noise restrictions in your neighborhood?
What type of fuel does it use?
How large is the fuel tank and how many hours of operation will it provide?
Is the generator easy to move around? Does it have built-in wheels and handles for portability?
What accessories will I need to run the generator (fuel, heavy-duty extension cords, transfer switch)?
Portable generators: A basic commercial-quality gasoline-powered 5 kW portable generator will cost around $600 or $800; an 11 kW generator about $2,300. These "contractor-grade" generators are designed to be hauled around and stand up to rough usage. While they cost more than you would pay for a retail store generator, the latter don't have the durability, dependability, and power that a portable generator from a dealer offers. You will also have difficulty finding service when your low-end generator needs repair - the usual solution being to toss it and get a new one. Renting portable generators is also a viable option, as prices can be as low as $75/week.
Stand-by generators: As a very loose rule of thumb, standby generators cost $300 to $500 per kW, installed. The prices listed below include delivery, setup, connecting to your business, and the required transfer switch, which can cost around $800 to $1,500 on its own.
12 kW: $4,000 to $6,000
15 kW: $4,500 to $7,000
25 kW: $9,000 to $13,000
40 kW: $12,000 to $16,000
75 kW: $20,000 and up
What is the difference between a 2 and 4 pole generator? Most small generators use a 2 Pole setup, meaning that the generator spins a single magnet (that has 2 poles) inside of a coil. In order to produce an AC signal at 60Hz, this magnet must spin at 3600 RPM. This is why most small engines, which can run at higher RPM's for longer period of times, utilize a 2 Pole configuration. A 4 pole configuration spins a set of magnets with 4 poles. Thus, in order to generate AC power at the same frequency (60Hz), the 4 Pole generator need only spin at half the speed of the 2 Pole generator, or 1800 RPM.
What is the difference between 1 and 3-phase power? 1 phase power is the type of AC power you are most familiar with. It is power delivered in a single sine wave. The downside of single- phase power is that the sine wave crosses 0 Volts 120 times every second. While this doesn't present a problem in a residential setting, most commercial and industrial setting require a more steady form of power. Three-phase power uses three sine waves, separated by 120°, to deliver near-peak power at any given moment in time.
What is Automatic Voltage Regulation (AVR)? AVR is a feature offered with many different generator models. The power produced by a generator is imperfect, as many factors can interfere with power output. If unchecked, these imperfections can lead to spikes and dips that can damage sensitive electronic equipment. AVR uses a number of power conditioning techniques to smooth out the power delivered by a generator, guaranteeing safe operation for electronics.
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