Using alternative CTs with EmonPi or EmonTX

Hardware
1

Hi I have long wanted to monitor electricity usage in our home but at circuit level rather than total consumption. I have joined the forum to ask a few questions before jumping into OpenEnergyMonitor as a solution to my needs.

  1. Firstly I have recently gone all electric (Solar to follow) and now have three ring mains and five radial connections in the distribution board to electric ovens and induction hob. The distribution board is therefore quite congested and there isn’t room for the standard clamp style CT to fit on each of the above eight circuits. My first quation therefore is can I substitute the SCT-013-000 with a fixed torroidal CT such as these
  1. I have chosen 30A CTs as that is the MCB rating and I assumed (perhaps incorrectly) the accuracy would be better than fitting a 100A CT Is it a matter of changing the value of the burden resistor or do you also have to make changes in the software code?
  2. I am completely new to Arduinos and coding although I understand the basics. Has anyone successfully substituted Clamp CTs with toroidal CTs for use with EamonPi or EamonTX systems?
  3. One final question. Has anyone successfully integrated OpenEnergyMonitor into Samsung Smartthings or Home Assistant?
    I understand all the warnings about having to disconnect mains cables in the fusebox. Although no longer qualified to current day standards,I was trained as an electrician and am competent to remove and replace a cable from an MCB.
    Many thanks in advance
    John
2

Welcome, John, to the OEM forum.

I think you might have picked up a lot of your knowledge about OEM from information published before the serious semiconductor shortages of a few years ago. Since then, we’ve moved away from the direct Arduino-compatible system (the Atmel ATMega 328 processor), firstly to the Atmel -DB series, and in development is a drop-in replacement for the present -DB devices using the much more capable ATSAMD series. This has enabled us to move to using the much more widely available 0.333 V output current transformers, so the present emonTx5 and emonPi2 (and their successors) all use those for the current sensor. We’ve also moved away from the 9 V a.c. adapter to use our own “emonVS” - a precision voltage source combined with a power supply for both the emonPi and the emonTx5. The result is much higher accuracy and the ability to have up to 12 inputs to one monitoring “node”. Also on the plus side for you (possibly), the c.t’s are that much smaller, both physically and in available current ratings. If this has come as a bit of a shock, I do understand.

So to your numbered points:

1.  You can do all 8 C.U. ways mentioned with the emonTx5 working to an emonBase by radio, or with an emonPi2 working directly into your LAN. Both need the 6-channel expansion board to give a total of 12 channels. As I intimated above, you can use any 333 mV output c.t., ring-core or split-core. The ring-core will generally be smaller and more accurate, and if you wanted to add lighting circuits, you’d probably get away with using a 5 A one.

2 & 3.  I think these questions have largely become irrelevant, the point of question 2 remains valid and it’s true - every c.t. becomes less accurate the lower the current (as a proportion of rated current) - it’s inherent in the magnetics. If you’re using the emonPi2, you’ve got in emonCMS the ability to calibrate each channel to the rating of the c.t. you use, if you have the emonTx5, then you need to connect it by USB cable to the emonBase, which runs emonCMS to do exactly the same. But you can load the appropriate software into a laptop and do it the way I do (i.e. basically edit-compile-upload but not using emonCMS).

4.  I don’t know about Samsung Smartthings (though I think I’ve seen it mentioned) but Home Assistant is definitely used by very many people here.

[Edit]
I was right - here’s a reference re heatpumps & Home Assistant: Samsung EHS mono 5kw settings - #30 by glyn.hudson

If you want to read about the present range, I suggest starting with (in the dark blue band at the top of this page) Docs →emonTx5 → Overview, then move to the emonPi2. I put your reading in that order only because you appear to be a bit familiar with the old emonTx (V3?). I reality, we now regard the emonPi2 as the principal device in the system with the emonTx5 offering a ‘remote’ capability.

3

Hi Robert,
Firstly thank you very much for your detailed reply and suggestions. I will first do as you suggest and read up on the newer emonTx5 and emonPi2. No doubt I will be back for some further advice but the fact you can use alternative toroidal CTs and of different current ranges looks hopeful.
Thank you again
John