From: Selecting A Generator
A generator must be properly sized for the load it will be used to handle. Electric motors are particularly difficult for a generator because starting an electric motor requires two to three times it's nameplate amperage or wattage. While electricity supplied by an electric power company has essentially infinite surge capacity (limited only by the circuit protection provided), a generator is limited by the engine horsepower and inertia of rotating parts. A current surge of short duration can be supplied by a generator, but a current demand of longer duration, such as a heavily loaded motor starting a high inertia system, can overload a generator possibly damaging both the generator and motor. A 3450 RPM air compressor motor is a prime example of this type of load. For this reason, when determining the power your generator is to provide, it is important to calculate electric motor requirements at three times the running watts to compensate for the surge needed to start the motor. With this in mind, the following guidelines will be helpful in selecting the right size generator for your needs.
- Total the wattages of all small appliances, tools and light bulbs to be operated at the same time. Most appliances have labels showing wattage (if volts and amps are given, volts x amps = wattage).
- Next determine volt-amperes (wattage) requirement of electric motors to be operated, remembering that the starting requires two or three times the nameplate or running (rated) watts. Thus, if running watts of the motor is 600, multiply the number by 3 to determine maximum V.A. needed. The starting (max.) V.A. can also be determined by referring to the motor code listing which indicates starting KVA per horsepower.
- Total watts and V.A. is Steps 1 and 2 to get total requirements.
- To allow for anticipated future needs or use of extra equipment, add 25% to total load in Step 3.
- See performance data charts at bottom of each generator listing for the unit that meets your total load criteria.
Equipment Running Watts Max VA Light Bult (100 Watts) 100 100 Radio 150 150 Fan 200 600 Television 400 400 Refrigerator (conventional) 400 1,200 Furnace Fan (1/3 HP with Blower) 600 1,800 Vacumn Cleaner 600 1,800 Sump Pump (1/3 HP) 700 2,100 Refrigerator/Freezer Combination 800 2,400 6" Circular Saw 800 2,400 Floodlight 1,000 1,000 1/2" Drill 1,000 3,000 Toaster/Coffeemaker 1,200 1,200 14" Chain Saw 1,200 3,600 Water Well Pump (1/2 HP) 1,400 4,200 Hot Plate/Range (per burner) 1,500 1,500 10" Circular Saw 2,000 6,000 Water Heater (storage type) 5,000 5,000 Electric Oven 10,000 10,000