Portable Generators

Portable Generators:

Careful preparation is essential to select, buy and install a backup system. Don’t leave it to the last minute- your household should have time to learn how to use the system in advance. And during a power failure, you may not be able to find suitable, reasonably priced equipment, fuel, and or installation.

Using a portable generators during a power outage can be a convenient way to keep your house comfortable and maintain a somewhat normal lifestyle. Portable generators are sold at home hardware stores, home improvement centers, and outdoor supply stores, as well as online. Prices range from $200 for small units that can power several light bulbs to more than $1800 for whole-house units. Some models have automatic electric starting capability. Better generators have an automatic shutdown if the crankcase oil is low. Larger units can produce both 120 volt AC and 330 or 240 volt AC for larger appliances. You can determine what capacity generator you need by comparing the wattage rating of the unit to the wattage of lights and appliances you intend to operate. Depending on fuel tank size, a generator may be able to operate for 2-12 hours between refueling. Do not plug a generator into an electrical outlet to feed power into your house wiring. Besides being illegal in most states, the generator can feed electricity back through the utility power lines and possibly electrocute those working to repair the power outage. It’s also likely you will overload the generator.

Connecting to a portable generator can be safely done two ways:

1) Direct hookup using extension cords to connect to lights and appliances. Use only heavy duty extension cords with adequate capacity to handle the wattage. Remember, the smaller the number rating means the greater the capacity ability. (i.e. an extension cord with a 12 rating can handle a greater capacity than an extension cord with a rating of 14 or 16). Do not connect more wattage than the continuous duty rating of the generator (the generator will slow down when it’s overloaded).

2) Permanent connection using a transfer switch. This provides a safe way to connect a generator and usually is installed by an electrician. It assures that no power from the generator can reach the grid. Because most people do not want to power their entire house, the transfer switch usually controls a sub-panel, which feeds a few circuits for lights, outlets, and critical appliances throughout the house. Be sure the transfer switch and all wiring meets requirements of your local building department and the National Electrical Code. Manual and automatic transfer switches for use with electric start generators are available. Locate the generator outside so exhaust fumes do not enter the house or attached garage.

If you hear the motor slow down while using the generator, it means the generator is overloaded. If a generator is overloaded for prolonged periods, it will overheat and shut down, and could possible damage the generator.

12 Volt Inverters: If you want to operate a few lights or small appliances, another possible power source is a small inverter connected to a storage battery. An inverter changes 12 volt DC power from a storage battery to 110 bolt AC power used by lights and appliances.

Compact inverters are sold at hardware stores, home improvement centers, and outdoor and electronic stores. Inverters are designed to plug into a cigarette lighter of a vehicle or to be connected to a deep cycle storage battery. Depending on the capacity of the storage battery and the wattage of what you’re trying to operate, inverters can provide power for several hours to as long as 1 day.

To maintain the life of a storage battery, no more than 50 percent of the rated capacity should be used before recharging it. Plug lights or appliances directly into the inverter or select the proper sized extension cord.

Using fluorescent lights with an inverter provides more hours of operation since they consume less energy than incandescent lamps. An overloaded inverter automatically will shut off from overheating.

A storage battery can be recharged with jumper cables suing an automobile alternator. If you use a non-sealed battery indoors, be sure to remember it is filled with corrosive, toxic acid and is very dangerous. Sealed batteries provide more protection.

If you plug an inverter into the cigarette lighter of a car, do not use it for more than a few hours before starting the car to recharge the battery. Car batteries are designed to provide high power for short time periods, not the slow, deep discharge needed for emergency power sources.

Calculating Generator Size:

The capacity of a generator or inverter is usually listed in watts. Many appliances are rated in amps listed on a specification plate on the back or bottom of the appliance. Keep in mind that motors, such as those used to operate a refrigerator or freezer compressor, take about three times more power (watts) to start up than to keep running. Most generators or inverters list both their continuous and temporary overload capacity.

The Ohms law formula converts watts and amps: Watts=Amps x Volts. For example: the blower on a gas room heater is rated 0.3 amp. What is the wattage? (The following calculation assumes the typical house voltage of 120 volts.)

0.3 amp x 120 volt= 36 watts

Start-up Power: 3 x 36 watts=108 watts temporary “overload”

Storage Battery Capacity: To determine how long a battery can power a light or appliance using an AC power inverter, you need to know the rated amp-hour capacity of the battery (this is not the “cold cranking amp” rating of automotive batteries). Use the Ohms law formula above to figure this example.

For example, a deep cycle 12 volt storage battery is rated for 50 amp hours. Using a small inverter, about how long could it power the 36 watt blower from the above example:

50 amp hours x 50% rate capacity=25 amp hours useful battery capacity 25 amp hours x 12 volts=300 watt hours battery capacity 300 watt hours/36 watts=8.3 hours of continuous power.

Recommended Extension Cords for Use with Generators: It’s important to use extension cords of adequate current carrying capacity when using a generator to operate electric equipment. Undersized cords result in excessive voltage drops and additional generator loading, as well as over heating and cause of possible fire. This can also lead to reduced performance of the electric equipment.

Wire Gauge for Various Extension Cord Lengths:

Watts 50 ft 100 ft 150 ft

240 18 ga. 18 ga 18 ga

480 16 ga 16 16

720 16 ga. 16 14

960 16 ga 14 12

1,680 14 ga 12 12

2,000 12 ga 12 12

For more Information:

Utility weatherization programs. Call the utility that provides your heating fuel (or the State Home Oil Weatherization Program for oil and propane heated homes) for a free energy audit to determine the best steps to weatherize your home. Call 1-800-452-8660.

American Red Cross. Order a copy of Before Disaster Strikes by visiting: www.redcross.org/disaster/index.html