As promised, a (non-technical) writeup about PZEMs.
What is a PZEM and what does it do?
A PZEM is a little device about 8cm x 3cm that measures the AC electrical power flowing through a cable. It does this by continuously measuring the current flow in the cable and the voltage applied to the cable. It's a bit more intelligent than a simple voltmeter and ammeter though because it also detects the timing of the current and voltage and can therefore calculate the Power Factor and Frequency. Knowing the Power Factor allows it to calculate the real power consumption which is what your domestic electricity meter records and what you are billed for by your supplier. It is accurate to 1% or better, typically 0.5%. The data interface is 5V TTL levels so it can communicate with any PC or microcontroller that will tolerate 5V signals.
Does it need to be installed by an electrician?
Not really. The PZEM has a terminal block with 4 screw terminals at one end. Two of the terminals are for attaching the current sensor (more later) and the other two are for connecting to the supply voltage. The current sensor can be clipped around the cable being monitored without disconnecting it and the voltage terminals can simply be connected to a 13A plug and plugged into the nearest mains socket.
OK that looks like an interesting toy but there are different PZEMs being sold, what's the difference?
The core gubbins of all PZEMs I've seen on sale are essentially the same although I've also seen ads for 'Version X' or 'Version Y' etc. I think these are probably just different revisions to the PCB or chips used. Read the ads and decide for yourself if 'Version Y' has something that 'Version X' doesn't.
Where they do differ is in what extra bits are supplied with the PZEM. Almost without exception they are supplied as just a bare unit and you have the option to include a plastic case (sometimes called a shell), a USB interface cable or both. There are also different types of current sensor (transformer) available. You have to choose a measurement range of either 0 - 100A or 0 - 10A, and how the transformer is fixed to the mains cable. It can be either 'solid' core or 'split' core. Solid or closed core means that you have to disconnect and isolate the mains to slip the transformer around the cable. Split or open core means that you can just hinge the two halves apart and clip them around the cable without disconnecting.
Which one should I buy?"
Unless you are building your own enclosure for a permanent professional looking installation* go for a 100A split core unit already in a case, plus the USB interface (NB. Some suppliers do not have a USB cable option so make sure that it's included or added). This means that as soon as you receive it you're ready to try it out and decide if you can be bothered to go any further. All you need to do is connect a 13A plug, clip the current sensor around the cable, install the software and possibly a driver, hook up your laptop and you're ready to go.
* I've noticed that there is now a version available that is already built into an enclosure complete with multiple 7-segment displays that show the running readings. I don't know any technical details so you're on your own with that one.
Mmm. Connecting a 240V doohickey to my laptop? I'm not sure about that."
The data interface is a 4 wire socket on the PZEM. Two wires carry data which are isolated from the 240V section of the PZEM by opto-isolators. The other two wires carry a 5V supply to power the isolators. Unless the unit is physically damaged or subject to condensation or water ingress there shouldn't be any problem.
Where do I buy one?
I bought mine about 18 months ago from BangGood but you can now get them from Amazon or eBay etc. (Other online retailers are available). Prices and delivery times vary so check around and double check that you've selected a 100A split-core with case and USB cable before you hit the 'Buy' button!
I'll show some example output and explain how mine is semi-permanently installed and talks over Wifi in another post but I think that's enough to get started. If I've missed something or anything's not clear, just shout.
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PZEMs new
PZEMs new