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Generator Sizing

Generators produce AC voltage, very similar to the voltage available in your home, however while your electric utility company produces sufficient power for all your electric powered devices, a portable generator is limited in power output directly relational to the engine horsepower. The amount of power that a generator can produce is rated in watts. Rated power is generally 90% of maximum power as certain components lose efficiency as they are heated from use.

To determine wattage requirements, you should determine which devices need to be powered simultaneously and what the starting requirement of the device is. Consider the maximum and rated power of the generator. This is important depending on what items you want to run off of your generator. Items such as toaster, lamps, and coffee makers are resistive, or constant/resistive loads and their total load can be calculated at amps x 1. Items such as saws and drills are reactive loads and while the running load may be small, the starting load should be calculated at running amps x 3. Remember, after the initial start less power is required for actual operation.

When calculating power requirements, consider the starting requirements are only for the initial start and then additional tools may be operated in addition. So 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.  Ohms Law of Physics (Watts = Volts x Amps) (Amps = Watts/Volts).

Contact our Member Services department here, or call 1-800-533-8658, for more information regarding generator sizing and what to consider before purchasing a unit.


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