Of all the conversations I have with potential customers, OEM and End User alike, this question comes up most frequently. Calculating load is crucial to sizing your generator correctly. To correctly assess your needs, one must look at amperage.
Amperage is the amount of current at any voltage that an appliance, motor or element needs to operate. Total amperage draw is used to calculate the minimum size generator. When determining this, always use the starting amperage or Locked Rotor Amps. While the running amps may be much lower, the starting amps are what will pop your breaker or overload your generator.
Environmental factors should be taken into consideration when sizing a generator. Ambient temperature, elevation and relative humidity all effect how efficient a generator will operate.
Once you have determined your minimum size and operating ambient environment the last step is to find the sweet spot. My suggestion is typically 70% of your generator's rated capacity.
If you have a consistent 10,000 watt load you don’t want to choose a 10 kW generator. That would be like driving your car 100MPH everywhere you go. It might do it for a while but it will wear out for more quickly with that kind of use. 70% seems to be the sweet spot between overworking the generator and under-powering it which could cause wet stacking.
For more information or assistance sizing a generator set for your project please contact the Power Tech sales department.