Building a DIY Home Power Monitor

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.

Background

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?

Simplicity.  Mainly.

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.

Finding Parts

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

Hobby Box

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.

Total Cost

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!

Final Thoughts

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.

– TPG

12 Replies to “Building a DIY Home Power Monitor”

  1. How good have you found the calibration of the power meter module, and how accurately does it read with complex loads like switch mode power supplies, motors etc. Is it true RMS reading?

    1. Honestly, I haven’t cross-checked it against a Fluke or similar. I was looking for insights from typical household appliances and aggregated loads over a long period of time. I would expect it to perform relatively poorly with more complex loads, but might be surprised. Let me know if you get one of the modules and do any testing! Cheers, Nathan

  2. Hi Nathan,
    Useful diy guide, thanks!
    My question is are you aware of any power monitoring products that don’t require being plugged inline? I want to measure a water cylinders usage fit about a month, and don’t want to have to pay a sparky to change from hardwired to three pin plug (and back).
    Cheers.

    1. Hi Adam,

      If you are comfortable doing so, the Peacefair monitor could be wired up to do this. You would need to disconnect the hot water cylinder and slip the CT over either the phase or neutral wire within the power cable, then wire it back up again. Provide power to the Peacefair unit from another source, and the CT measures power flowing through the hot water cylinder cable.

      Alternatively, if you are looking for a more ‘off the shelf’ solution you could try a Clamp Meter (Google it) which is basically a multimeter with an integral CT that clips (clamps) around a cable. Again, you’ll need to be able to access either the phase or neutral wires individually. This will tell you instantaneous current, but may not do the longer term monitoring.

      There are some domestic house monitoring units with clip over CTs, but they tend to be more focused on commercial customers and are freaking expensive ($500+), or have monthly monitoring charges, or both.

      If it was me, I’d try using the Peacefair unit.

      Cheers,
      Nathan

  3. The alliexpress site says it works at 220v. Is this a problem with nz at 240v..
    I too would like to use it to measure my hwc consumption.
    Thanks

    1. Hi Todd. Check out the very bottom photo. Voltage, Current, Power readings are instantaneous. Energy is cumulative – and is reset by round button in right hand side. Cheers, Nathan

  4. Hi Looks great, What are the outside dimensions of the box Please, my supplier is confused about a size 6 box ? do you have a link on where I can get it Thanks
    Cheers
    Steve

    1. Hi Steve. I have one Jaycar box and one Banggood box. I think they are called hobby boxes. Dimensions of my ones are approx 200mm h x 150 w x 60 d. Cheers, Nathan

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