1. Enter the Amps.  Useally the amprage of the equiment is listed on the equipments name plate label
  2. Select the Voltage:  120 or 220 volts
  3. Select the Duty Cycle:  The duty cycle is the percentage of this the equipment is actully running, thsi is sometime listed on the name plate label if it is an appliance.  Some appliances that you may be backing up such as a refrigerator may be on 100% but has a compressor/motor that turns on and off.  typically a refrigerator has a duty cycle of 25-30%
  4. Select the model you are interested in purchasing. 

The result will be the runtime the selected model will support the load. 

If you are trying to size a battery back up system you may also find our battery bank calculator tool usefull. 

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