Hi,
In case I would like to have more measurements, means to acquire a second Iotawatt, my question is the following:
Is it possible to share the CT for the 3 main phases between 2 devices? Or do I have to connect 3 additional?
Thanks
Not possible. Sorry, but you might also try using derived reference (one mains CT/IoTaWatt) and see if the results are satisfactory. You may be surprised.
HI,
there I’m a bit confused, when you speak about derived reference like in the wiki (Home · boblemaire/IoTaWatt Wiki · GitHub)
you have anyway 1 CT per phase, this means 3xCT… and on this post you speak about 1 mains CT per IoTaWatt…
It’s me that was confused. Sorry. You’re right, both methods require 3 CTs. It’s one VT vs three with derived reference.
You can’t share the CTs. You will need three more for the mains on the second IoTaWatt if you want to measure the mains on both. If you are uploading the data to influxDB or EmonCMS, then you probably don’t need to measure the mains again with the second IoTaWatt.
But if I do not connect the mains on the second device, how do I declare for the CTs what is the reference phase?
You should be able to share the voltage reference (VT) between the two Iotawatt whether you use one or three VT. Will need a cable adapter.
Each input on both Iotawatt needs its own CT.
The phase reference comes from the VT(s). If you were to delete the mains CTs on your first IoTaWatt, you would see that it will keep logging power for all of the other inputs.
In the interest of being specific about how to do this exactly, it would be helpful if I knew whether you are using Direct (3 VTs) or Derived (1 VT) reference.
If you are using Direct reference, the phase of any particulat CT is implied by the voltage reference that you select for it. For Derived reference, you will select phase A, B or C for any particular CT, with phase A being the phase of the VT.
Hi, I’m using derived reference
Reviving this old thread… I am considering multiple iotawatt devices on a 3 phase setup but only have one device connected to the 3 voltage refs? I have a 3 phase (currently multiple emontxv2 talking to each other via i2c) set up in one location with 3 separate AC-DC references but the other distribution boards for the iotawatts are too far away and I don’t want to put separate outlets on each phase at these locations. If there is no easy way to share the data over serial or wifi then I guess I could omit the voltage reference altogether and then do post processing in emoncms to scale the various iotawatt outputs by the true voltage feed?
The bad news is that you need to have a voltage reference for IoTaWatt. The good news is that you only need one to do derived reference.
The overwhelming majority of IoTaWatt three-phase installs are derived reference, and there are many. Given that you seem open to a solution that uses VA instead of Watts, there should be no reluctance to using derived reference, which is much more accurate.
If you currently have Ideal VTs on the TXs, they are compatible with the IoTaWatt, and the CTs should be as well.