Moonson Power Meter Calculations

Energy

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# @author Huber Flores
# source: http://electronicsclub.info/power.htm 
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#Calculate energy consumed from power

The amount of energy used depends on the power and the time:

<Energy = Power × Time>

A low power device operating for a long time can use more energy than a high power device operating for a short time. For example:

* A 60W lamp switched on for 8 hours uses 60W × 8 × 3600s = 1728kJ.
* A 3kW kettle switched on for 5 minutes uses 3000W × 5 × 60s = 900kJ. 

The standard unit for energy is the joule (J), but 1J is a very small amount of energy for mains electricity so kilojoule (kJ) or megajoule (MJ) are sometimes used in scientific work. In the home we measure electrical energy in kilowatt-hours (kWh). 1kWh is the energy used by a 1kW power appliance when it is switched on for 1 hour:

1kWh = 1kW × 1 hour = 1000W × 3600s = 3.6MJ

For example:

* A 60W lamp switched on for 8 hours uses 0.06kW × 8 = 0.48kWh.
* A 3kW kettle switched on for 5 minutes uses 3kW × 5/60 = 0.25kWh.