Watt Meter for True RMS Measurement up to 1500W

Figure 1 

The project was designed to build an accurate watt meter which will be used to measure different power levels.

The watt meter circuit was a modification from the original project which contains a 0.001 Ohm copper shunt that provides a scale of 1000 Watts. This circuit was made to have a range of zero to 1500 Watts since most circuit breakers in homes are having 15A current. The project also uses a shunt that is comprised of 5 small loops in a single piece of wire. The wire was designed in an inverted V shape or an N shape that goes from pad to pad.

The specification of wire to be used such as wire size and length will depend on the range of wattage that is desired, and in this project, a #16 AWG wire was used although it is a bit small. For the 1500 Watts, the wire could be a longer #14 or even #12 AWG. Heating and resistance changes can occur when small shunt wire is used.

The watt meter circuit cannot be used on rectifying loads because it was made to measure power on the negative cycles only without a transformer.

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