3 Phase Import and Export Monitoring

Hi I have a 3Phase Anaerobic Digestion plant which is generating about 44kW some of the time when there is enough gas available. I have been looking at the kit was wondering i anyone could give me some advice on what kit I would need to enable me to accurately monitor what is generated and when not generating then what our consumption from the grid is. At the moment I am thinking I am going to need at least 2 x emonTx and 8 CT clipon sensors 4 for the generation side and 4 for the grid consumption side. Also 2 x AC adapters for to power the emonTX’s and provide the reference voltage. Im thinking I may need an Emonpi and maybe network adapters for the emontx’s

could someone put together a kit list for me please.
regards Matt

Why 4 c.t’s?
And will the emonTx’s be within radio range of the emonPi? If so, they can communicate that way.
Otherwise, the ESP8266 will give you a cabled connection (and then you might want the emonBase rather than the emonPi).

Other than that, your list looks reasonably correct. You’ll need to add a programmer and the miscellaneous cables.
I’m guessing you have other plant, so you want to measure the nett grid power and the generation separately.

I can fill in more details later.

Hi Robert
Thanks for the quick response. I thought you needed 4 CTs one for each
phase and then one for the neutral or have I got this wrong. I would
probably have the EamonTx next to the emon pi or emon base so they could be
wired in directly. When you say I need to add a programmer what do you
mean by this?
Yes the plant should exceed our energy requirements but when it isn’t
running I would like to see what we are consuming from the grid so that I
have an idea if what the bill should be. If you wouldn’t mind filling in
more details that would be much appreciated.

Kind regards

You have. You don’t need the c.t. on the neutral. The neutral current is the vector sum of the three phase currents, and if your three phases are accurately balanced, it will be zero. If they’re not, you will have some neutral current. The worst case is when one phase is fully loaded and the other two are zero, when the situation is the same as your (single phase) home supply, and the neutral current is equal to the line current.
So 2 sets of 3 c.t’s then. The standard 100 A split-core c.t. should be fine, on both grid and infeed.

emonPi or emonBase? The difference is the emonPi comes in a nice aluminium case and has one voltage, two current, temperature and pulse inputs and a RFM69CW radio - internally it’s a RPi with a cut-down emonTx and a LCD display; the emonBase is a RPi with just the RFM69CW radio.

Unfortunately, I don’t think you can have two serial interfaces with a Raspberry Pi.

Our normal means of communication is via the RFM69CW radios, which the emonTx has as standard. You can disable that, or just not take any notice of it, and add an ESP8266 (Ethernet) module, but it will cost you a 5 V USB power supply too because the a.c. adapter can’t supply enough current. So I’d recommend staying with the radios. (But if all 3 units are together, one sufficiently beefy 5 V d.c supply could power all 3.)

I mean this. You’ll need it to load the configured and calibrated 3-phase sketch into your emonTx’s, because they come with a single-phase sketch as standard. Download from GitHub and look at the 3-phase sketch, to make sure you’re happy with its limitations (spelled out in the comments at the start), before you go too far.

If you’re not happy with the limitations of the three-phase sketch, then the more accurate method is to have an emonPi measuring one phase, and the two emonTx’s measuring one phase each. You’ll combine the powers and energies in emonCMS just the same.

Hey Robert sorry for the late response, this is a hobby project and my work was getting in the way lol.

So I think I will need the following
At the power generation location

  1. 3 x CT clipon sensors
  2. EmonTx
  3. 2 x AC adaptors
  4. EmonPi

At the main incoming supply (500m+ from the power generation)

  1. 3 x CT clipon sensors
  2. EmonTx
  3. 2 x AC adaptors
  4. EmonBase

Then I will need to download the 3phase sketch (can you send me the link to where I can download it from, I have signed up with Github but couldn’t find it.

Then I need to somehow load the sketch onto the emon pi to look at the emontx connected to it and also the other emontx via the emon base and internet

Does that sound about right?

(Also I measure the current on the neutal and it was showing 6 Amps when the plant was at 50% power generation. will this be an issue?

Kind regards


Sorry Robert I also forgot to ask what is the resolution of the emoncms monitoring? can you increase the frequency to once per second?

kind regards


The 3-phase sketch is here: https://github.com/openenergymonitor/emontx-3phase

The default log interval is 10 seconds, you can decrease that if logging to a local emoncms, but make sure you’re sending data (from the 3-phase sketch) more frequently than your input logs to a feed, otherwise you end up with lots of “missing data”. As an example (from experience!), if the input is getting data every 2 seconds and your feed is trying to log every 2 seconds, all it takes is for the input to be delayed by 0.1 of a second (due to radio interference for example) and you’ve lost that data point.

I’m not sure about your hardware list. You don’t need an emonBase, all that does is add radio capability to a Raspberry Pi, and you’re using serial only. You don’t mention the USB 5 V power supplies that your emonPi / emonBase will need, and you might be able to economise on a.c. adapters too. Your emonBase doesn’t need an a.c. adapter. If you power both emonTx and its associated emonPi from the 5 V d.c, you can share the a.c. voltage reference too (be careful with polarity, check the schematics).

I take it the anaerobic digester has some local loads, so doesn’t feed all its output back to the main incomer?
And check your main cable sizes. The SCT-013-000 is good to 25 mm2, but you’ll need something different if yours is more than 12 mm O/A diameter.

I don’t think that will be necessary. The serial connection is to the Pi, not to the emon sub-unit. So you shouldn’t need to touch the sketch in the emonPi.

The limitation of 10 s is for emoncms.org, so as to allow everybody a fair share of resources. On your own system, you can do as you like (limited usually by data storage space in the long term).

Glyn Your advice on connecting to the Emon pi worked brilliantly thanks Glyn

Do you by any chance have a dummies guide to setting up the emon Pi / emonTx for 3phase energy monitoring.

I have a laptop which i am using to connect to the Pi and the Pi is communicating with the emonTx.

I believe i need to load the configured and calibrated 3-phase sketch into your emonTx’s.

I have just bought a “programmer” and i assume i plug one end into the UART connection and the other end i use a USB lead andpug it into my laptop.

I have downloaded Python 3.6, ATOM and also downloaded the files for the 3Phase sketch from the Git hub you directed me to.

Problem is I dont know what to do next and I have never used Python or ATOM before.

Any help would be much appreciated

kind regards


I’m not Glyn, and there isn’t a dummies guide. The “official” way to load the sketch is somewhere in “Resources” and uses an editor-based script called Platformio that I found screwed up my whole system. I (and others) prefer to stay with the proper Arduino IDE, which you can download from the official Arduino website. You’ll need to install it, and some libraries, and if you say your OS (Windoze, Mac or Linux), I can supply details, because they’ve been deleted from here.

After that, you can plug in as you described, and set about calibrating your sketch. Details are in the comments at the top of the file.

Thankyou Robert.
So am I right in assuming the emontx is arduino based? My laptop is windows
10 os

Kind regards

Indeed - or to be totally exact, it uses the same Atmel processor as the Arduino Uno, the Arduino IDE can be used (select “Uno” as the board) and libraries written for the Arduino will largely be useful for you.

Here are the instructions for installing the IDE and libraries.
Installing IDE (Win10): https://community.openenergymonitor.org/uploads/default/original/2X/e/ea18e0f77a100b08d23c27ce82e1949b847fa3ba.pdf
Installing Arduino libraries (Win 10): https://community.openenergymonitor.org/uploads/default/original/2X/6/663f8f3493da62d2eac8c6265b32b18d317e3de3.pdf

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