In the past, I have used off the shelf power monitors for checking appliance power consumption at home and for my friends and family. Typically this is an old fridge, freezer, dryer etc.
However, I keep breaking them (yes… it might be me!).
Feeling like I am constantly throwing money away, I set out to build a reliable power monitor for less than $50.
In the past, I have gone through a few of the Elto EMA-1 power monitors which can be picked up for around $25 from Mitre 10 and online.
They are a pretty useful device, rated for loads up to 10A. However, for me, they haven’t lasted that long. Typically with the screen failing or the power monitor unit refusing to turn on after 12 – 18 months.
So, I wanted to build something more flexible and more reliable.
My Power Monitor Requirements?
I have used a number of power monitors and loggers over the years, from $25 up to many thousands for commercial grade power-quality loggers.
For home use, my main power monitor requirements were:
- Off-the-shelf parts
- Simple to use
- Robust and reliable, and
- Less than $50 to build.
My favourite site for random electronics is Banggood. If you haven’t come across Banggood before, it’s a reliable Chinese site that is kind of like Amazon and Ebay had a baby. It sells an amazing array of useful and truly strange stuff.
Power Monitor Brains – Peacefair PZEM-061
There are quite a few different power monitor modules/panels on Banggood from $10 to $30.
I ended up settling on the most commonly purchased module, the Peacefair PZEM-061. This has a current rating up to 100 Amps AC, which is a lot more than the 10A rating of the Elto unit.
In the box, you get the module, CT and basic wiring instructions all for $13.85 delivered to my home in NZ. Deal.
Power In & Power Out
I wanted to be able to plug a device or two directly into my power monitor (similar to retail devices like the EMA-1) and also have a decent power lead so I could rest the monitor somewhere convenient.
Popping down to the local Bunnings store, I picked up the following items:
- DETA double powerpoint – $7.88 incl. GST
- Arlec 2m extension lead – $2.96 incl. GST
To put everything together I looked at a few options before settling on the typical ABS plastic hobby box for electronic projects.
As I was impatient, I initially purchased a dark grey ABS box from our local Jaycar store for $30, which formed the basis for my first monitor. To save money, I purchased a second from Banggood for $11.24.
The total cost for the power monitor was $35.93 plus a 10-day wait for the key parts to arrive from China.
Putting It All Together
If you are not comfortable with wiring up electronics at mains voltage, I would not recommend doing this yourself.
I have spent some time as a residential electrician, so am more than comfortable myself.
I cut two holes in the front panel of the hobby box to mount the screen and powerpoint. Then I drilled a hole in the side slightly larger than the diameter of the power cord, chopped off the female plug and fed the end through.
Here’s the box before the internal wiring is completed:
Next came the internal wiring, which broadly looked like the diagram below.
Note that the measurement module power should be taken off before the CT, to avoid the module measuring its own power consumption. I made this mistake initially, powering the module from the powerpoint – this adds approx 1 Watt to the load measured. Not a lot but it adds up over time.
Finally, electrical insulation and safety testing of the appliance before putting into service. All good!
I’m very happy with how the power monitor has turned out. Below is a picture of the finished unit in operation, measuring our kitchen kettle.
The price was well within budget at only $35.93 for the parts. This was only a few dollars more than the unit I was looking to replace and it both looks and feels a whole lot more robust.