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BigGrey · 05-31-2012, 11:36 AM

Not promoting Honda Generators or products but found this article quite informative and thought it may help others.

How much power do I need?

Determining the power required by an appliance

Maximum vs. Rated Power
More help:

Home applications
To determine your basic home power needs, start with these three questions:

Do you use city or well water?

Well pumps require a larger 240 volt generator (3800 watts or above).

Is your heating system electric, heat pump, or gas or oil forced air?

Gas or oil forced air systems can get by with a very small generator – as little as 2500 watts. The power needed is based on the size of the furnace fan motor. See below for details.
Electric furnaces and heat pumps typically need 15,000 watts or more to run and cannot be powered by a portable generator.

Is your hot water heater electric, gas, or oil fired?

Gas or oil fired heaters use less power – as little as 2500 watts.
Electric heaters often require at least 4500 watts.
Homeowners can often power most household appliances using between 3000 and 6500 watts.
If your home has a smaller furnace and city water, you can generally expect that 3000-5000 watts will cover your needs. If you have a larger furnace and/or a well pump, you will likely need a 5000 to 6500 watt generator.
More help:

Recreational applications
RVers:
The primary factor you need to consider is the size of your AC unit(s).

The EU3000 Handi and EU3000is will power most 13,500 BTU AC units
Larger AC units may need two EU2000i’s paralleled together.
The EU6500is works well for fifth wheels and RVs with dual AC units.
The AC’s needs may vary based on many factors, including the ambient temperature and the efficiency of your model. Your dealer can help you to select the best generator for your individual situation.

Campers, Tailgaters, and Boaters:

Usually 1000-2000 watts will handle most needs.
Check the power requirement of your blender, coffee pot or other appliances you want to use.

More help:

Industrial applications
Industrial power needs range widely, based on what kind of tools you are using. To determine your power needs, start with our wattage estimation guide can help you to build a quick estimate. Simply choose the tools you will be using and add up the wattage.
Keep in mind that wattage required for starting a tool or appliance with a motor will be much higher than the watts required to run the device. See more about starting vs running wattage below.
If you need the wattage on a specific tool, see our section on determining the power needed by an appliance below.
See our section on power management to learn how to use a smaller generator to power more.
Determining the power required by an appliance
Most appliances and electric motors list their power requirements in amps. Typical locations include:

A stamp on the bottom or side
The nameplate
A data tag is found on all electric motors.

Keep in mind:

Appliances with electric motors need additional power to start – up to 3 times the amount to run. More info about starting vs. running wattageOlder appliances may require more power than what is listed. This is because they become less efficient over time.

Use an appliance load tester to determine the exact power needed for a variety of tools and appliances. Honda offers a handheld load tester that is perfect for this job. This inexpensive tool is available from any Honda dealer.
Our Wattage Estimation Guide also provides average wattage for many applications.
How do I convert amps to watts?
Appliances frequently list their power requirements in amps. Most generators list their output in watts. Fortunately, it’s easy to convert from one to the other:

Watts = Volts x Amps
Amps = Watts/Volts

Most appliances use 120 volts. See our wattage estimation guide for a list of 240 volt applications.
If you have two of the numbers (e.g. volts, amps) then you can find out the other (e.g. watts). This can help you to determine the rated power that you’ll need from your generator.
Starting vs. Running Wattage
Some appliances require extra power to start up, while others maintain the same power requirements constantly.
To calculate your power needs correctly, you need to know which kind of load you are dealing with. (A load is defined as the device that you are powering.) There are two kinds of loads:
Resistive loads
Resistive loads are pretty simple: they require the same amount of power to both start and run the equipment. Many resistive loads are involved in heating or making heat of some kind. Examples of resistive loads include:

Light bulbs
Coffee maker
Toaster

Reactive Loads
Reactive loads contain an electric motor, which requires additional power to start, but significantly less power to run once it gets going. Typically starting power is 3 times the amount of power to run the application. Examples of reactive loads include:

Refrigerators / freezers
Furnace fans
Well pumps
Air conditioners
Bench grinders
Air compressors
Power tools

Some household appliances, like a furnace or refrigerator, have internal fans that come on intermittently. Extra wattage/power is needed to start the fan each time. Refrigerators also have a defrost cycle that requires power in addition to the compressor and fans.
Reactive loads may also require additional power when the electric motor begins to work. For example, when a saw begins cutting wood, its power requirement will increase. This is not applicable for most household appliances.
My appliance is a 1000 watt model, but it takes 1600 watts to run it. Why?
Some devices are labeled or promoted with a power number. For example, a hair dryer might say "1000W." This means the hair dryer itself produces 1000 watts of heat energy. But the amount the hair dryer uses from a power outlet is always more than it produces in heat. This is because the device’s energy use is not 100% efficient.
Another example is a microwave oven. It may be marketed as "1100 watt oven" and indeed produce 1100 watts of cooking power, but it will require more than that from a generator.
Translating the data tag:
For some appliances, you can determine the power needed by looking at the data tag supplied by the electric motor manufacturer.
All electrical motors should have a data tag attached to their bodies that give volts, amps, phase, cycles, hp, and sometimes a code.

Volts (V) - The volts must be either 120 (110-120) or 120/240. 120/240 means that the motor can be wired to operate on 120V or 240V. Honda generators are either 120V or 120/240V.
Amps (A) - Indicates the amps required to RUN the electric motor but doesn't consider STARTING or LOADED power requirements.
Phase (PH) - Honda Generators can only power single phase motors.
Horsepower (HP) - Rating of how much work an electric motor can perform.
Code - This isn't always provided on the data tag. It represents the maximum STARTING power required of the electric motor. You can multiply the code (amps) times the Horsepower of motor to determine starting amps. Find a list of codes and the amps here.
Cycles (Hz) - All U.S. electrical appliances run at 60 cycles per second.

To determine the wattage needed, use Amps x Volts = Watts
Maximum vs. Rated Power
Generators are often advertised at the maximum wattage they can produce. But you’ll also see the “rated power” listed.

Maximum power = the maximum output that a generator can produce. Maximum power is usually available for up to 30 minutes.
Rated power - the power that a generator can produce for long periods of time. Typically 90% of the maximum power.

In general, use rated power to determine if a generator will be able to adequately power your applications continuously.