Watts Used by Common Appliances and Tools (Usage Guide)
When selecting an inverter, choosing the right size is essential based on your power needs. For example, if you’re considering a 500W inverter, you might opt for a larger one to accommodate additional devices, like running a fan while using your computer or letting the kids watch TV.
Understanding Continuous Load and Starting (Peak) Load:
To determine the appropriate inverter size, consider both the continuous load (the power your device needs to run continuously) and the starting (peak) load (the surge of power required to start up the device). Some appliances, especially those with motors, need a higher initial power surge to start before settling into a lower continuous load.
Key Terms:
- Continuous Load (e.g., 2000 watts): The ongoing power required by the appliance.
- Peak Surge (e.g., 4000 watts): The initial surge of power needed to start the appliance.
Helpful Formulas:
- To Convert AMPS to WATTS:
- Multiply: AMPS × 120 (AC voltage) = WATTS
- This gives a close estimate of the appliance’s continuous load.
- To Estimate Startup Load:
- Multiply: WATTS × 2 = Starting Load
- This approximates the starting load, though some appliances may need a higher starting surge. Note that devices like air conditioners, refrigerators, and pumps may require 3 to 7 times their continuous rating to start.
Example Calculation:
For a freezer with a continuous load of 4 amps and a startup load of 12 amps:
- Continuous Load: 4 amps × 120 volts = 480 watts
- Starting Load: 12 amps × 120 volts = 1440 watts
In this case, you’d need an inverter with a peak-surge rating greater than 1440 watts.
To Convert AC Watts to DC Amps:
- Formula: AC Watts ÷ 12 × 1.1 = DC Amps
- This calculation helps determine the size of the vehicle alternator needed to sustain a specific load. For example, to handle a continuous draw of 1000 watts, you’d need a 91-amp alternator.
