Generator Sizing

DETERMINING YOUR ENERGY NEEDS

BECAUSE WITH A GENERATOR, SIZE MATTERS
The first thing you need to do is determine what size generator would work best for your particular requirements.

This section will help walk you through that process.

When purchasing a generator, it’s important that you select one that’s capable of meeting your energy requirements.

bulletYou must match the rated output of the generator to the maximum anticipated power to be used.

This section will assist you in estimating the power requirements so you can purchase the generator that will satisfy your needs.

bulletThis includes using the accompanying worksheet to make a list of the tools and appliances you expect to operate, as well as the approximate power requirements for each device.

Once you have the list, you can estimate the highest demand that will be put on the generator under the “worst-case” conditions. With this figure, you can determine the appropriate model Yamaha generator for your particular needs.

WARNING: Electrocution, severe personal injury or death can occur: Do not connect any generator to any building’s electrical system unless an isolation switch has been installed by a licensed electrician. Refer to the Generator Owner’s Manual.

CAUTION: Property damage can occur: Do not connect any generator to any building’s electrical system unless an isolation switch has been installed by a licensed electrician. Refer to the Generator Owner’s Manual.

TAKE IT STEP-BY-STEP
Follow these steps when determining your energy needs:
 

1. 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

2. Add up the required watts of all the tools and appliances you expect to operate simultaneously.

3. The total watts derived in step 2 is the size Yamaha generator you need. These three simple steps will “size” a generator. Normally, you won’t need to consider motor starting requirements when using a Yamaha generator. When a Yamaha generator is properly sized for a tool’s or appliance’s running requirements, Yamaha’s surge capability usually is sufficient to handle the motor’s starting surge needs.

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:

G EN E R A T O R   W O R K S H E E T
 
RUNNING
WATTAGE REQUIREMENTS
ADDITIONAL STARTING WATTAGE REQUIREMENTS
TOTALS
HEATING/COOLING:
Furnace Fan, gas
or fuel oil furnace
 
  
1/8 horsepower
300
500
 
1/6 horsepower
500
750
 
1/4 horsepower
600
1000
 
2/5 horsepower
700
1400
 
3/5 horsepower
875
2350
 
Central Air Conditioner
 
 
 
10,000 BTU
1500
2200
 
20,000 BTU
2500
3300
 
24,000 BTU
3800
4950
 
32,000 BTU
5000
6500
 
40,000 BTU
6000
6700
 
HEATING/COOLING:
SUB-TOTAL:
 
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 
Freezer 2500 2200 
KITCHEN  SUB-TOTAL: 
BATHROOM   
Hair Dryer 800 – 1700 0 
Iron 1200 0 
BATHROOM  SUB-TOTAL: 
APPLIANCES   
Lights- Wattage Actual:  
VCR 50 0 
Heating Pad 65 0 
Radio 100 0 
Television – Black & White 100 0 
Television – Color 300 0 
Dehumidifier 400 0 
Electric Blanket 400 0 
Garage Door Opener – 1/4HP 550 1100 
Garage Door Opener – 1/3HP 725 1400 
Well Pump – 1/3 hp 750 1400 
Well Pump – 1/2 hp 1000 2100 
Sump Pump – 1/3 hp 800 1300 
Sump Pump – 1/2 hp 1050 2150 
Vacuum Cleaner – Standard 800 0 
Vacuum Cleaner – Deluxe 1100 0 
APPLIANCES  SUB-TOTAL:  
COMMERCIAL PRODUCTS:   
1/4″ Drill 300 300 
Jigsaw 300 300 
Electric Weed Trimmer 500 500 
Router 1000 1000 
Belt Sander 1000 1000 
Disc Sander 1200 1200 
Chain Saw 1200 1200 
Worm Drive Saw 1560 3100 
12″ Concrete Cutter 1800 3600 
7 1/4″ Circular Saw 1500 3000 
Disc Grinder 2000 4000 
Air Compressor, Average 2000 4000 
COMMERCIAL PRODUCTS:  SUB-TOTAL:  
   GRAND TOTAL 

ADDITIONAL GUIDELINES

CONVERTING AMPS OR HORSEPOWER INTO WATTS
If necessary, use these formulas:

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.

bulletAdd a 10% correction factor to your totals to help overcome this uncertainty.

If your customer plans to operate devices that use electric motors, list both the starting and running requirements of each.

bulletStarting 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.

MOTOR/
DEVICE
STARTING
WATTS
RUNNING
WATTS
Motor A2,600850
Motor B1,300600
Motor C1,000750


 

 

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:

bulletNo electric motors.
bulletOne motor running at a time.
bulletMore 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.

bulletFor 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 EF2800i, that can produce 2,500 watts rated output, is recommended.
 DEVICE  WATTS
 Electric Skillet  1,500
 Light  100
 Heating Pad  65
 Total:  1,665

NOTE: The EF1600’s rated output is 1,400 watts, so its output would be too low to handle this load on a continuous basis.

Footnotes:
*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 that power.