Have you ever wondered what appliance consumes the most in your house? This unit will give you a comparative visual output so you will what it is. This is basically a monitor that logs your consumption via SD card. The analog voltage and current signals are gathered and computed by the formula P = V x I. At a rate sample of 9615 Hz which is quite accurate. An LCD displays the power consumption by bar graph and doubles as an oscilloscope to show the voltage and current consumption wave forms.

The current reading is very accurate since it has a setting for high and low power consumption. Current measurement is gathered using a transformer installed on the fuse box. It is made from discarded TV fly back cores and using magnet wires wound 100 turns. A resistor with .2 ohm is connected in series with the coil and wrapped in electrical tape. USB or shielded wire cables can be used for connections between sensors and apparatus. Since the two cores give different readings using the same data input it would be better to test some cores and get the one that would give an almost same reading as the other one. The quad op-amp LMC6484AIN is used to amplify the signal due to its ability of working peak to peak using a single power supply.

The AD623AN amplifier is used since it can use input even below ground that is utilized as earth ground and circuit ground as a damper for voltage divider. The voltage is gathered on a 2000:1 ratio. The components used are computed for 120V input but can easily be re-computed for 240V if required.

The analog board is located inside a metal box that is grounded to stop interference from surrounding 60Hz radiation. The fly back sensors, one for each phase, should be installed properly and be careful of accidental short circuits. The output can give from a day or a week’s comparative power consumption.

http://www.stahlke.org/dan/powermeter/