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Michael Taylor - 2nd Place (Trinity Place Selkirk, New York)
Power Consumption Analyzer
Downloads for this project:
All files and information © 2006 Michael Taylor.
Project Description:
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Click on Image for a close-up
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As power costs increase, it is becoming more desirable to understand the amount of power being used by appliances. The Power Monitor is designed to display the amount of power being used by an appliance or any load under 13 amps. The Power Monitor plugs into a standard 115 vac receptacle and the load is then plugged into the Power Monitor unit. The front panel display then indicates the amount of power being consumed by the load. The unit has two ranges for improved accuracy at low power levels. The low range indicates power from 0 to 150W to a tenth of a decimal place and the high range indicates power from 0 to 1500W to the nearest whole number. In addition to displaying power, the unit also calculates the Root Mean Square (RMS) voltage and current delivered to the load.
The Power Monitor takes multiple instantaneous voltage and current samples during an ac cycle to calculate the average power consumed by an appliance or load. Each voltage and current sample occurring at the same instant in time is multiplied and then summed together. Dividing this result by the number of samples taken during an ac cycle yields the average power consumed by the load. To accurately compute power, multiple samples during an ac cycle are necessary, requiring a high-speed microcontroller. Since this project requires a high-speed microcontroller to perform the fast sample rate and to compute the power, the SX Microcontroller was chosen. The SX Microcontroller operates at 50Mhz, which allows for samples to be taken at a high rate while still being able to performing math intensive functions.
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Click on Image for a close-up
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Computing power by using multiple instantaneous voltage and current samples yields the average power consumed by any load, including loads with a non-unity power factor or loads where current is not conducted over a complete ac cycle. For instance, most compact fluorescent light bulbs used in the homes today have a power factor of 0.5 to 0.6, meaning that the product of RMS voltage and RMS current may yield a power twice as much as actually being used. Additionally, components with transformer based rectifier circuits will draw a large current over a small portion of the ac cycle yielding an inaccurate power based on the product of RMS voltage and RMS current. Thus, with the Power Monitor’s calculation technique, it is able to accurately calculate power being delivered to these types of loads.
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