Determining Your Generator Needs
Wed Feb 25, 2009
We all use our generators in many different ways. At home, on the ranch, construction site, campground, park, backyard, beach—anywhere we want to have power and land lines are not accessible. The one thing we cannot do with our generators is get more power from them than their maximum output, so evaluating your needs and what equipment you wish to use at any one time is critical in deciding what size generator to purchase.
You want to keep in mind the maximum and rated output of the generator you intend to purchase. You will be attaching items which have reactive loads (circular saws, pumps, drills, air conditioners and air compressors, fluorescent lights). Other items commonly used will be standard light bulbs, coffee makers, curling irons and frying pans. These items have resistive loads. A resistive load of 600 watts draws 600 watts from your generator. The reactive load items draw much more on startup and a good rule of thumb is 3 times the run load rating. So if a drill has a run rate of 600 watts then 600 x 3 = 1800 watts is your calculated need for the drill.
Maximum output is available to assist in motor starting only. The generator should only be operated at maximum load for no longer than 30 minutes or damage to the generator will result. (Owner’s manual warning.)
Many times a number of items are plugged into your generator. Your management of what is operating at any one moment is critical for proper operation of your generator.
Review the power requirements of each of the items you wish to run. Calculating the proper run load requirements is the best way to determine your actual needs. Below is a chart with many common items and their power requirements. Keep in mind your tools and appliances can vary from these averages.
Simple Calculations
Ohm’s Law
Watts = Volts x Amps
Amps = Watts/Volts
Other considerations to review prior to your purchase
Normal operating altitude
With any generator your power will reduce by 3.5% for every 1000 feet above sea level.
Average ambient temperature
Again with any generator your power will reduce 1% for every 10 degrees over 85 degrees.
Extension Cords An extension cord must have adequate wire size (AWG or American Wire Gauge)An extension cord must have adequate wire size (AWG or American Wire Gauge) for safety, and to prevent loss of power for safety, and to prevent loss of power and overheating. The smaller the gauge number of the wire, the greater the capacity of the cable, i.e. 16 gauge has more capacity than 18 gauge. When using more than one extension cord to make up the total length, be sure each individual extension cord contains at least the minimum wire size.
