What Size Generator Do I Need?
Before choosing a generator, you will need to decide what you will be using it for, and what types of devices you are going to be running with the generator.
Step 1. List all of the devices you plan on using with the generator
Step 2. Identify the wattage requirements for the tools and appliances that you want to power. The power requirement for the tool or appliance can be found on its identification plate or in the Owner’s Manual. If the power requirement is given in amps, multiply the amps times volts to derive the required watts.
Amps x Volts = Watts
Step 3. Add up the required watts of all the tools and appliances you expect to operate simultaneously.
The total watts calculated in step 3 is the size generator you need. These three simple steps will “size” a generator.
The Additional Guidelines section explains the procedures to calculate and size for motor starting.
This chart lets you immediately add up all of the appliances you will most likely utilize:
|ADDITIONAL STARTING |
|Furnace Fan, gas or fuel oil |
|KITCHEN|| || || |
|Refrigerator, Average||600||2200|| |
|Dish Washer – Cool Dry||700||1400|| |
|Dish Washer – Hot Dry||1450||1400|| |
|Clothes Dryer – Gas||700||1800|| |
|Clothes Dryer – Electric||5750||1800|| |
|Microwave Oven, 750W||750||800|| |
|Washing Machine||750||2300|| |
|Coffee Maker||850||0|| |
|Toaster – 2 Slice||1100||0|| |
|Toaster – 4 Slice||1650||0|| |
|Electric Skillet||1500||0|| |
|Electric Range 6-in element||1500||0|| |
|Electric Range 8-in element||2100||0|| |
|Television – Black & White|
|Garage Door Opener – 1/4hp|
|Garage Door Opener – 1/3hp|
|Vacuum Cleaner – Standard|
| || || |
CONVERTING AMPS OR HORSEPOWER INTO WATTS
If necessary, use these formulas to assist in sizing your generator:
Watts = Amps x Volts
Running Watts* = Horsepower x 932** (for motors)
Remember, this worksheet lists average power requirements — a particular manufacturer’s device may use more or less than the listed wattage. Add 10% if you are not sure.
If your customer plans to operate devices that use electric motors, list both the starting and running requirements of each.
Starting requirements of some devices maybe significantly higher than their running requirements. This higher demand must be considered when estimating your power needs. Some small, universal motors — which do not draw a heavy starting load (drills, small saws, blenders, etc.) — require very little extra current for starting.
When listing items that use motors, take them in the order of highest-to-lowest starting requirements, as shown in the example below. Motor A, for instance, has a starting requirement of 2,600 watts, so it’s listed first, followed by Motor B at 1,300 watts, and Motor C at 1,000 watts.
Once you have compiled an accurate list of what you will be operating, you can calculate the maximum power requirements. There are three different calculations you can make, depending upon the kinds of tools and appliances on the list, and their intended use:
- No electric motors.
- One motor running at a time.
- More than one motor running at a time.
NO ELECTRIC MOTORS
If your list does not include any devices that use electric motors, simply add the power (running) requirements of all the items on your list to
obtain the maximum power needed.
- For example, if you intend to use only an electric skillet, a 100-watt light and a heating pad (as shown below), the maximum power requirement would be 1,655 watts. In this case, a generator like the EG2500 or EN2500, that can produce 2,300 watts rated output is recommended.
NOTE: The EU2000’s rated output is 1,600 watts, so its output would be too low to handle this load on a continuous basis.
*Running Watts is the amount of power a motor consumes once it has started to run at normal speed.
**932 is the factor used to convert motor horsepower ratings to needed electrical energy. It takes into account normal losses in utilizing