A handy 230VAC 10A inline power meter based on an inexpensive module from eBay

This article describes a simple and inexpensive inline power meter for use as a test instrument.

CNC routing

The box cutouts were done on a CNC router, but they could be done with hand tools.

Above, calcs of feeds and speeds for the CNC router. The box is actually ABS, but cutting speed for Polycarbonate is the same.

Above is the tool path for one side of the box. The cutouts suit the 7P-2 strain reliefs. The gcode is generated from a custom Python file using a custom library of common shapes that I use.

Above, the box cutouts were done on a CNC router.

Above, the tool path for the box bottom to receive the power meter module.

Power meter module

Above is the power meter module, about $23 on eBay. Using the current transformer seen, it is rated for up to 100A, but the cord set used is only good for 10A.

The module displays voltage, current, real power and accumulated energy (kWh). Power factor can be calculated as \(PF=\frac{RealPower}{ApparentPower}=\frac{power}{voltage \cdot current}\).

For example, if I measure an air compressor near maximum pressure, I get \(PF=\frac{RealPower}{ApparentPower}=\frac{power}{voltage \cdot current}=\frac{2250}{239 \cdot 10.22}=0.92\).


Parts list:

  • box;
  • power meter module;
  • extension cord;
  • 2x Heyco 7P-2 strain relief bushings;
  • bootlace terminals, end splices; and
  • self adhesive rubber feet.

I might mention that the closed end splices used are NOT the cheap Chinese knock offs with soft aluminium ferrules.

You will need to strip sufficient cable to be able to wire using the end splices.

Above, controller wired and ready to be fitted with the bottom lid.

Above, the completed power meter.

Do not undertake this project unless you have the requisite competencies and experience.