New user setup help in the USA - emontx and emonpi

Hi all,
With Glyn’s help I’ve been able to get my system installed and sending data to emoncms, but I still need help tweaking the system to work properly. I have a schematic drawing of my system, but new users can’t upload images so I’ll do my best to describe it.

First I’m in the US, so we have a split phase system, with two 120V legs feeding my meter from the street (plus neutral and ground of course). Due to the layout of my property what I have setup is an emontx with the SCT019 clamps. CT1 is clamped on one of the 120V main feeds from the street and CT2 is on the other 120V feed. I’ve got the USA AC adapter plugged in there and everything seems to function (i.e. I can “see” the emontx on my emoncms inputs).

Next I have a 3.5kw solar system feeding into a sub panel in my house next door to the main panel in another building. Same type of setup: two 120V feeds from the solar feeding into the sub panel. which in turn feeds into the main panel. So I setup my emonpi there with the SCT013 clamps. CT1 clamped on one of the 120V feeds from the solar, and CT2 clamped on the other 120V feed. This also seems to function fine, and I can see all it’s data on emoncms as well.

Now, the trouble is all the numbers are incorrect because I’m sure I need to reconfigure a few things and I’m not quite sure how, such as:

  1. I think I need to use the DIP switch in the emontx to use it for USA power systems? I presume I just need to open it up, flip the switch (where/which one?) and reboot it?

  2. the emontx needs to be reconfigured in emonhub? to use the larger SCT019 clamps, right? I see the instructions on how to do that in the shop page with those clamps, but I’m using one each on CT1 and CT2, so I’m unclear exactly how to do that for more than one. Then I presume I need to sum those two numbers to get an accurate consumption number?

  3. The emonpi gives me a negative number on CT2, positive on CT1, so I need to reconfigure it to monitor solar production only on both CT1 and CT2. I’ve already used emonhub to reconfigure to “USA 110V” but still need to get CT2 positive. I know I can flip the CT2 clamp around and that should happen, but don’t know if it would be better to do this in emonhub instead?

As you can probably tell I’m a novice when it comes to coding, networking, etc, but I’m capable with a little help. Thanks!

I’ve raised your permissions by one notch, so you should be able to now.

That’s correct. Here’s the PCB legend annotated with some notes: EmonTx V3.4 - OpenEnergyMonitor Wiki

Right. You can do it by adjusting the numbers for “scales = …” in emonhub.conf for your emonTx (to get the right one - look at the Node number on the Inputs page and locate the section with that number inside the double square brackets).

The standard SCT-013-000 current transformer is rated at 50 mA out per 100 A in, the SCT-019 will give you 33 mA per 200 A, which (although it exceeds the maximum current) would work out at 303.03 A to give 50 mA. Therefore, you need to alter the first two values in “scales = …” from 1 to 3.0303
(The numbers in each line map 1:1 to the names above.)

Indeed you do. But you can kill two birds with one stone here:

If you want CT2 on its own positive, you can either change the "scales = " for power 2 to -3.03, or you must go to the inputs page in emonCMS and add a process to multiply by the constant value -1 Don’t do both.
If you don’t want CT2 on its own, then you can subtract CT2 from CT1 in the processing of CT1 to get the sum: Click on the spanner for Power1, in the first box pick “- input” and pick “power2” in the second box, then add this operation. If you wanted to multiply by -1, you’d have picked “x” under Calibration in the first box, and -1 in the second. Or if you’ve already made CT2 / power2 postive, you must of course add it to power1. (Save it before you leave that page!)

If you are sending all the separate powers to separate feeds, then (for complicated reasons) it’s better to use “+ feed” or “- feed” rather than “input” when adding the powers of the two legs.

One thing worries me: You must NEVER clamp a ferrite-cored current transformer onto the cable. There should never be any pressure on the ferrite core, because it is exceedingly brittle and can easily snap, which destroys its properties completely and renders it useless. You must only clip it over the cable so that there’s only its own weight at most pressing on the core.

Is that enough to get you going? Post again if/when you need more help.

Thanks Robert! I will attempt all and let you know how it goes before I ask more questions. My goal ultimately is to integrate all this monitoring with my openEVSE so I can enable eco mode and charge our car with excess solar power, which we generate at various time throughout the day.

And to put your mind at ease regarding the CTs when I said clamped on I really meant clamped AROUND. :wink:

off we go…

Much progress!

On the emontx (main power into house) side of things:

  1. I opened up the emontx to find that it was already switched to USA mode when it shipped out (good customer service right there). The other switch was set to node 10, which I presume is where it should stay?

  2. I then recalibrated for the larger 200amp CT clamps and it worked like a charm! Now I’m getting better numbers, though power1 is positive and power2 is negative? This is where my lack of knowledge about an entire electrical system is going to fall short. It’s a nice sunny day so we are generating power, so in theory I guess either of these numbers could be positive or negative. But I have no way of determining if the numbers are accurate. In any case unless I’m told otherwise I’m going to presume those numbers are right for now, and I need to add them together in emoncms to get my total power?

On the emonpi (solar generation) side of things:

  1. I did as you said in emoncms and set up a log to a feed that subtracted power2 from power1, which nicely gave me total power being produced, currently a nice 2.8kw!

one other thing I have noticed. On the emonpi I get a vrms reading of 114.8, and on the emontx I get a vrms reading of 111.1 (roughly. These figures change slightly here and there but not by more than about .3). With my multimeter on those outlets that the AC adaptor is plugged into I get a reading of 120.1 - 120.6V. Can or should the vrms reading match that more closely? I’m wondering if this is part of that change I made in emoncms configuration to switch from UK 220 to USA 110, and shouldn’t that USA number be 120?

Thanks again!

To a large extent, you can use whatever NodeID you want (0 < NodeID < 31), but choosing one of the standard ones is more sensible than picking a random number and then having to change everything to fit. The major concern is the Node ID identifies the source of the data, so if you have two the same, the data mixes together and can never be separated.

NodeID = 10 has the node name “emontx1”, so it’s a good one to choose. Likewise NodeID = 9 is good for your second.

Have you read this: Learn→Electricity Monitoring→AC Power Theory→Use in North America→Use in North America
That tries to explain how you should set up your hardware.
Our convention is imported power & energy is positive, exported is negative.

They should match exactly - but they won’t, due to component tolerances. Again, like you tweaked "scales = " for the c.t., you can tweak the corresponding number for both to read the same as your meter. But it won’t affect the power calibration! The calculation of power is done in the analogue front end of the emonPi and in the emonTx, before it reaches emonHub. If you’re reading roughly the right number, don’t mess with the USA config setting. That’s just a flag, NOT a value. Logically it should have been USA = true.
You can read the description of how it “works” here (if you want to get totally confused :nauseated_face: ): Help EmonPI Questions
Yes, I know the USA voltage is 120 V, 110 V is a common voltage here for controls and portable tools, and the UK voltage is still centred on 240 V.

OK, getting close. I have read the “use in North America” section a few times. A little complicated for me but I get the general theory. I did notice that in Figure 2, which is what I have set up, one of the CT’s is flipped opposite the other in the drawing. Mine are both facing the same direction. Do I need to flip one, and which one? This would make some sense to my laymans logic in that both my power1 and power2 numbers should be positive (i.e. representing power that we receive from our utility) unless we are generating excess solar power in which case it could be negative. Is that right?

Once I get the correct power1 and power2 numbers on the emontx I presume I need to add them together, similar to what I did for the emonpi monitoring the solar, except that I’d add them together instead of subtracting the negative from the positive (which in that case accomplished the same goal of total power generated)?

Yes you do. You reverse the one that gives a negative reading when importing.

That’s right.

Already done and now I have two negative numbers, since I am making excess solar right now. But I’m having trouble summing the power1 and power2 figures. I basically followed the same instructions as I did to get my solar output from the emonpi, but instead of choosing the “-input” I used “+input” on the emontx power1 and selected power 2 in the next box. Once I created the feed and looked at it the number isn’t right. Currently the two feeds are -842 and -1058, indicting, correctly, that we are exporting power to the grid. But in the feed which is supposed to add those two numbers together it is -2290. What am I missing?

This is the emonTx input/feeds in emonHub?

It shouldn’t do that! The way the calculations on the inputs page work is the raw value starts off at the top then (for the most part) that number is operated on and the result is passed down the page to the next operation.

What operations are you doing on each of the inputs before you send to the feed?
Assuming you want to be able to save and display the two legs separately as well as the total, what I think you need is:

In power1 ‘input’ processing:
  log to feed “A leg power”
  + feed “B leg power”
  log to feed “Total power”

In power2 ‘input’ processing:
  log to feed “B leg power”

That should give you three feeds: the two grid connections separately plus the sum.
I’m not an emonCMS expert, what I don’t know is whether there is a timing issue in there, so you might need to experiment by moving the ‘+ feed’ etc into the power2 process.

It worked! I guess I’m still learning the processing side of things, but with a little trial and error and your instructions I now have everything reading correctly. I couldn’t have done it without you Robert. Thanks for helping out a novice! I’ll play around with this for a bit and get more familiar with it before I start trying to integrate my openEVSE and charge the car in eco mode. Thank you!!!

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