Hello folks. I am thinking on how to setup an IoTaWatt in Brazil in a house with a solar system, and want to check if my understanding of the required parts are right.
Brazil uses a 3-phase (Called R, S, and T respectively) + Neutral (N) system. Phase-Neutral is 127V, and Phase-Phase is 220V.
Is my understanding correct that I will need 3 120V AC Reference transformers, and not the 220V reference transformer?
On a separate note, do I need 1 or 2 Current Transformers for the Solar inverter input into the system? It’s a single-phase inverter as shown in the diagram below. Sorry for the terrible art work.
Your plan is fine except that I would recommend using a single AC reference transformer with “derived reference”. The phase-phase 220V for the inverter would be derived anyway.
EDIT: The 120V AC wall transformers are rated 120V. I cannot say what would happen if used with 127V and the possibility of higher voltage of say 133V at +5%. At a minimum they would use more power and therefore heat up more. You would have more experience with this issue and would be a judgement that you would need to make at your own risk. Use of any type of voltage converter to step down to 120V would most likely have a significant impact on both accuracy and phase shift.
A better choice would be a 6V-12V transformer that is made for 127V. You could calibrate it with a meter.
IoTaWatt is potentially capable of using a 230V Euro style transformer connected to the 220V phase-phase. It would require some changes in the configuration app to present parameters to derive and set the individual 127V phases. We would need to work together to do that.
Thank you for replying @overeasy.
Are there any reason to go with a single AC reference transformer (and derived reference), except to save on costs (of 2 additional transformers)?
The documentation talks about “The disadvantage is that large variations in voltage between phases may result in decreased accuracy.” and it would be something interesting for me to monitor given it’s an area prone to regular power outages due to heavy rains (1x/month roughly). Not unherad of one of the phases being off in voltage after such events out there.
Ack on the 127V issue you described. I might be willing to buy an extra 230V Euro style transformer and work with you and the forum to derive the individual 127V phases. Might be a cool feature to have - tons of solar installation going on in Brazil as well.
There is the cost of the transformers, but also the cost to make two additional plugs available that are wired to the other phases, and the loss of two inputs that could be used to monitor additional circuits. I have no data on installed sites, but judging by the number of kits that have been bought with three VTs vs the number of three-phase users that seems to be out there, I’d estimate that over 95% of sites use derived reference. I have no recollection of anyone trying it and coming back for more VTs because of an accuracy problem.
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Really cool that you have those sale stats. Thank you for the answers @overeasy, I’ll be getting those parts and installing the system later in the year (construction is still ongoing), and will report back once it is up and running, hopefully with some photos as well.
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