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Measurements don't make sense

Tags: #<Tag:0x00007fc345a4bec8> #<Tag:0x00007fc345a4bdb0>

Hi, I installed a emontx v3 with wifi and 3CT+temp, AC-reference+DC supply around the beginning of Jan and connected it to emoncms online to visualize the data. But the measurements are not making sense. Just to give some basic numbers:

Service: 25A 3Phase

Top consumers:
5,4kw EV charger (2-phase combining into 1-phase)
9kw (3-phase) Heatpump
2kw EVSE charger (1phase)

Generation capacity:
5,5kw PV (Facing east, south-east)

  1. Top power usage is lower than expected.
  • Looking at the graphs in emoncms, I would expect 5kw+2kw draw normally at about 17:00 CET as the total system draw at least. (PV generation is minimal (below 100w) during this time), but I see only about 3,5-4kw max, spread over 3 phases. I charge one nissan Leaf that’s depleted until 20%, and one completely depleted phev.
  1. The heatpump cycle shows as negative for one phase.
  • I think I’ve identified the heatpump cycle, but two phases show the draw as positive, and one phase show it as negative with the same load profile (ie visual representation of the load, only inverted). If I reverse the CT on that phase, I get a proper representation of the heap pump draw, but the normal load on that phase is 500w negative, showing exported power during night time, which is impossible. (see attachment)
  1. The PV production should visualize as a 3-phase banana :slight_smile:
  • Currently one of the CT’s is inverted in regards to the current flow indicators on the CT, and the PV production is reasonably represented as a 3-paralell banana. (see attachment). But if the current indicators are facing the same way, one of them indicates an inverted power curve during PV production times?

Initial thoughts:
I must have done something wrong. Does it matter which order the CT’s are connected to the emontx? Something related to phase shift?
I checked the installation instructions again, and while the fit is tight (rigid thick cables), there’s play and not forced. I’ve changed the dip switch to use DC for power.
I’ve also tried to replace the CT, since I had one spare, no change.
Could it be calculating UK power, like 120v or similar? Could explain the lower calculated power than expected.
I used a fairly low end clamping clamping current meter to check the current on one of the phases, and it seemed to be accurate.
Measured [email protected], 3*256/1,71 (=449w, which at the time showed approx 495w locally. The square root of 3 was off the top of my head so it was off by 0,02.

Any help welcome.


Here’s a snapshot on how the load looked like with the CT in normal orientation.

Welcome, Mats, to the OEM forum.

Have you loaded the sketch for 3-phase systems?

The sketch that is loaded when you receive your emonTx will be for the UK single phase system. If you have not changed it, then the phase with the a.c adapter should be correct, the other two will probably be negative and showing approximately half of what you expect.
If you download the zip file from this link, you will have the full documentation and installation instructions as a PDF file.

You will need to install the Arduino IDE to configure and compile the new sketch, and to load it into your emonTx you will need a programmer.

Thank you, I’ve had a look around the forum and there’s alot of info from other members. If I just get the basics sorted I’ve got plenty of inspiration for other uses :slight_smile:

I wasn’t aware that there’s different firmware if I use it in Sweden compared to UK. I have no programmer, so I will need that then. Is there any way I can confirm that I have the UK “sketch” now?

If you are using the sketch (= Arduino-word for “software”) that was in the emonTx when you bought it, and you did not ask for anything different, it is the UK single-phase version.
The easy way to confirm that, without a programmer, is to put all three or four c.t’s on the same cable facing the same way. If all read the same value (within a percent or two), it is a single-phase sketch.

Hi, sorry for the late reply, but yes, I got it confirmed that the emontx was delivered with UK firmware, causing these odd measurement results. I’m ordering a programmer and loading the firmware you specified.