THE BUYING GUIDE TO PORTABLE GENERATORS
COMPARISON, REVIEWS, SELECTION, PRICING
THE BASICS.
Frequent blackouts and growing awareness lead to increasing interest in backup power solutions. Portable electric generators (or gensets) are designed to temporarily supply AC power during the electrical outages or in locations where grid is not available. As the name implies, this type of devices is for stand alone (non-hardwired) applications. Such devices are normally used to energize a few critical appliances via extension cords (although high-end models can power an entire home and can be used as a supplementary energy source in off-grid solar power systems). Besides residential application, portable gensets are utilized on construction sites, farms, motor homes, recreation vehicles, and in camping trips. Currently, they are available for sale in the range of 500W to 17.5kW. They are generally cheaper than home standby systems and may be used right away without any professional installation.CHOOSING THE FUEL TYPE.
Depending on the design, genset's engine can run on gasoline, diesel, biodiesel, propane, or natural gas.Gasoline-powered devices generally cost less then other types of gensets. You can buy for example a 4000W gas model for about $350. The main problem with this type is when the grid is down the gas pumps may not work. To assure a backup electricity during a wide-spread blackout you would need to store a substantial supply of stabilized gasoline. Note that unstabilized unleaded gasoline has very short shelf life- it can begin breaking down in about six months and will gum up the fuel system. Some stabilizers are claimed to extend gasoline shelf life to two years. So, you would need to replace your supply of stabilized gasoline at least every other year. Alternatively, for a few hundred dollars consumers can convert practically any gas-fueled engine into a multi-fuel one with a third party conversion kit. Note that if not properly maintained, a gasoline engine may have cold weather start up problems due to gum deposits. All gas engines require frequent maintenance such as periodic oil, filter and spark plug changes.
Portable diesel generators are more efficient, more quite, have the longest engine's life, but generally are the most expensive. Diesel also is the least flammable fuel source and has longer then gasoline shelf line, but it likewise may not be available during a blackout.
Propane can be easily stored in large tanks, has practically unlimited shelf life, and besides natural gas is the only type of fuel normally available during wide spread outages.
There are also multi-fuel devices that offer more options when one type of fuel is not available. Usually a simple field adjustment is needed to switch from one type of fuel to another. They may cost almost the same as a permanent system with the same wattage, but you save on the electrical installation.
FEATURES/OPTIONS.
When choosing a genset, aside from rated power, type of fuel and cost, there is a number of features and accessories to consider. Cheap models may sound like a lawn mower. Check if there are any noise restrictions in your neighborhood. Quiet models normally cost more. Besides this consider the following useful features: OHV engine, electric start (in addition to manual recoil), 30 or 50 A twist-lock receptacles, GFCI for additional safety, and oil gauge. Since a typical model may weight several hundreds pounds, look for wheels kit- devices with wheels can be moved around by one person. If you want a clean sinusoidal voltage for sensitive electronics, you need the devices with inverter technology (which may cost typically twice more than regular gensets). Also, for a peace of mind it is preferable to have a model that is listed with the Underwriter's Laboratory (UL) or FM, or a respective safety agency in your country. See our comparison chart for ratings, features and prices of top-ranking models.HOW TO CONNECT A PORTABLE GENERATOR.
The most common method of hooking up your AC loads is by using extension cords. You plug the cords into your genset outlets and run them through an open door or window to the appliances you want to power. Be sure to use heavy duty outdoor-rated extension cords. You will need 3-wire cords for 120VAC outlets and a 4-wire cord for 120/240V. The required wire size depends on its length and the rated load current. As a rule of thumb, AWG #12 cord is sufficient for currents up to 20 A. Instead of running individual extension cords, you may use a 4-wire extension cord set that plugs into the high-current locking 120/240VAC receptacle of your generating set and provides several female outlets on the other end. Likewise, for a 120V locking outlet you can get a 3-wire cord splitter.The extension cords method perhaps is your only option if you are looking for a quick solution. However your lights, boiler, central a/c and everything else that is directly connected to your house wiring will not be powered- you will need to figure out how to disconnect them one by one from the building wiring system and then connect to the extension cords. You would have to go through all these troubles every time you need to use a generator. A more convenient and safe method is to hook up your backup power device to the house system via a professionally installed transfer switch. The transfer switch isolates genset from the grid and prevents power backfeeding into utility lines, which can hurt utility workers and is illegal. It also protects your genset from damage if power returns while it is running. Once you wired it, all you need to do is roll out your genset from a storage and connect it to the transfer box via a single power cable that plugs into generator's high-current twist-lock receptacle. You can either buy such a generator cord or just buy a plug and a socket and build it by yourself: see the diagram below for the pinout of a single phase 120/240V 30A plug NEMA L14-30. The method with a transfer system is safer and gives you more flexibility. However it increases the cost of your setup, requires professional installation, and may cause problems if your genset has GFCI and internally grounded neutral. For your safety, be sure to turn OFF the main circuit breaker BEFORE starting the installation.
SAFETY.
Your owner's manual will include the recommended safety rules. However you need to know certain basic things in advance to plan your layout.- Just like all engine containing devices, electric gensets should always be used OUTDOOR at least 15 feet away from the house to avoid carbon monoxide poisoning and, fumes build up.
- A genset should never be connected directly into a wall outlet or your house wiring unless they are isolated from the grid.
- Most portable generators need to be protected from rain and snow.
For prices on some of the top rated models which you can buy from a leading online retailer, visit our Discount generators page.
See Material Connections Disclosure.
THE BASICS AND DIY TIPS
REVIEWS, SELECTION GUIDES, SAFETY TIPS
Understanding emergency power systems
Building a homemade generator from a lawn-edger motor
Lightplants and homemade generators
Consumer Reports review and buying guide
OSHA safety fact sheet
Understanding portable generators features and terminology
© 2005, 2007-2010 L. Rozenblat