Sunday, March 3, 2019

Kogan Energy Monitor Teardown - Sonoff-Pow in a wall plug

After doing a tear-down on the TPLink Wall Plug energy monitor I found mentions in Australia of the much cheaper Kogan Alternative. So I decided to get a couple of them see what makes them tick as well.
General Assembly of the whole unit

TL;DR - The Kogan one is cheaper because it uses a bare metal (non-linux capable) CPU and a PWM output type energy monitor (without intricacies of a SPI protocol and calibration). It is essentially a repackaged Sonoff Pow.

The details of the build are packages in sections as I discovered them.

LV and Buck converter

The LV section consists of two separate cricuits:
  1. Relay to switch the load
  2. Buck converter to rectify and convert 240v to 5v to power electronics
The diagram below presents both of these sections. The Buck converter is basically the toplogy found in many aliexpress products. Perhaps with the difference of being unisolated (notice no slots). The relay is rated at 15A which is nice compared the TPLink product which uses x2 - 5A relays in parallel to achieve 10A.

Low Voltage (240v) Circuitry

Energy Monitor and LDO

This a 3.3v operated section which uses the super low-cost PWM output energy monitor IC made popular by the Sonoff the measure instantaneous voltage, current and hence power. The pulses are channeled to the main processor for forwarding to whatever backend Kogan has put together.

Metering and LDO

Main Processor

The design seems to have taken a standard ESP module and planted it on a basic PCB to fit in the power-plug form factor, sideways. The carries board has lots of markings and test-points making the task of reverse engineering and putting new firmware on this board almost too easy.
Processor module adapter
Marked bottom test pads of processor carrier PCB
Over all this looks like a nice certified unit which you can run your own firmware on thanks with the help of the right triangular security bit.