Design Considerations and Construction of Digital Wattmeter for Measuring Solar Charge Controller

This paper describes the design considerations and construction of digital wattmeter. The system describes the current drawn by the load flows through parallel-connected resistors, which turn the current into a proportional voltage. Then amplified and applied to the one input of four-quadrant multiplier. The voltage divider resistors sense voltage across the load and applied to another input of four-quadrant multiplier. The measuring ranges can easily be changed by means of selector switch. The single-ended level shift op amp stage converts the differential output of the multiplier to exactly the value of 1mV per watt. The display circuitry interprets this value and then the corresponding power can easily read out on the digital LCD display. This small device can measure power up to 3.5 kW. The whole unit is powered by regulated power supply of ±7.5V. This device can also be used to measure the power of solar charge controller.