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EmonTX Solar Split Phase US

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Hope everyone is doing well and safe. I have in my set-up with my emonPi an emonTx. They are working as expected. I would like to used my emonTx for monitoring solar generation only. My question would be if a can set-up CT1 and CT2 in the Solar PV app as solar generation only and not Grid export/import like in Type 2. Also is it possible to add CT1 plus CT2 like the emonPi for monitoring both phase at the same time?
The emonTx is connected to my solar generation split phase inverter and everything looks good. Thanks in advance for your help.

Best regards,


Welcome Alexander to the OEM forums.

Is your Solar PV feeding in at 120 V, or is it across both legs at 240 V? If it’s the latter, my guess is the neutral connection is only used for the control gear, and if that’s the case, you can forget the tiny error ignoring that will introduce, and you will only need one c.t., You then double the power/energy in the maths in emonHub, using the coefficient in “scales = …”. And of course that uses only one input channel of the emonTx.

You only need two c.t’s if there is significant neutral current. If that’s so, then ideally, you should modify the sketch and add the two currents, powers and energies before sending the data to your emonPi (for exactly the same reason - the numbers are processed sequentially and it’s possible for the A & B legs to get out of step). If you don’t want to edit and reload the sketch in the emonTx, then it’s easy enough to add the two inside emonCMS.

Thanks for the welcome!

Yes the Solar PV it’s feeding in at 120 V each leg. I’d selected Solar type 2 for monitoring in the app but there’s only one option for Solar generation. Ok then let me search some information about modifying the sketch to add the two currents also double the maths. Thanks for your help!

You’ll find the download in Github. It’s NOT the “obvious” file that claims to be the “official latest”, but the Continuous Monitoring one further down the page: EmonTxV3CM.

The bits you’ll need to change are (possibly - depending on what you want to send) the definition of the data structure to transmit the data around line 70, and the place where that’s filled with the numbers around line 273.

I guess all you’ll probably want to do is something along the lines of
emontx.P1 = EmonLibCM_getRealPower(0) + EmonLibCM_getRealPower(1);
but if you want the powers etc for each leg separately as well, then you need to create (say) P12 inside that struct and then assign the sum to that.

Having done that, if you change the struct, then you must change the entry in emonhub.conf accordingly. If you don’t, it’s going to throw it out as corrupt data.

If you only use 1 c.t, then (assuming it’s channel 1 that you’re using and it’s Node 15), then the emonhub.conf entry becomes

  nodename = emontx3cm15
    names = MSG, Vrms, P1, P2, P3, P4, E1, E2, E3, E4, T1, T2, T3, pulse
    datacodes = L,h,h,h,h,h,l,l,l,l,h,h,h,L
    scales = 1,0.01,2,1,1,1,2,1,1,1,0.01,0.01,0.01,1
    units = n,V,W,W,W,W,Wh,Wh,Wh,Wh,C,C,C,p
    whitening = 1

[Note the ‘2’ twice in scales = …]


Thanks for the explanation, found the files and lines you refer of. Before doing any changes. In the photo attached, is it possible change "House or Building use in Watts” to “Solar pv generation”? So that way I can select each PV phase for Solar monitoring.

I pass on that. You need someone who knows a lot more about emonCMS than I do.

Hi Robert,

Ok thanks for all your help. Will keep searching for information.

No, that would undermine the purpose of the app which is to compare usage and generation, showing self consumption and export. If you use 2 generation feeds you would get some rather odd/useless results.

You should combine the PV feeds for each phase in emoncms first.

If you want to see each PV phase individually in an app, use 2x “myelectric” apps, one for each phase. They will then each just show the generation for the one phase without any confusing nonsensical calculations.

1 Like

Hi Paul,

Thanks for the info. Will try to combine the PV feeds in emoncms, first need some reeding and in modifying to be sure not to messup anything.
Also look the option 2x “myeletric” app if it’s an option for me, would prefer to be in the “solar” app to see the performance of solar generation. Thanks again!

It’s actually one phase, split into two legs.

Semantics, I know, but definitely not different phases, e.g. 3-phase.


I do understand US supplies Bill as you well know.

I am replying to the users last post, where he refers to “each PV phase”

I have not read the whole thread, however my comments stand regardless of whether you are summing legs or phases, or even different roof aspects, strings or properties.

Feel free to correct Alexander if you feel the need, but as you say it’s semantics.

OK, but I wasn’t aware you do, or if you’ve mentioned it, I’d forgotten. :wink:

Oddly enough, true two phase power was used in the US in the early 20th century, and it’s still in use
in Philadelphia, Pennsylvania and Hartford, Connecticut. So maybe more of a rarity than semantics. :grin:

I’m not sure I fully understand what is being said here. However, I have setup a PV system in the US and wrote up some thoughts here. Obviously the serial connection aspect doesn’t apply but some of the other information may be useful.

Thanks for sharing your feedback @montgomeryb I’m still reading and studying how to modify and upload the firmware. Just don’t want to messup anything.

You’ve found the article in ‘Learn’ about installing the Arduino IDE and Libraries? I can support you with that, I can’t help you with platformio - it screwed up my machine, so it hit the bit bucket - fast.

Thanks for the follow up @Robert.Wall . Yes I found the article for installing it for Windows. I’m looking to this one now

I’m afraid that if you use platformio, you’re on your own. I cannot recommend it, when I tried it, it screwed up my machine and cost me hours getting rid of it and putting everything back. There are no such problems with the Arduino IDE. All you need to do with that is download the libraries and the sketch as per the instructions, then it should be one click to compile and upload the sketch to your emonTx.

Yes I will use the Arduino IDE. I’m searching where to buy in the US the USB to UART adapter. Thanks!

You need the RTS line to be able to put the processor into programming mode, as well as the usual power, gnd, Rx & Tx.
The FTDI LC231X is the one you want,

Thanks for the link @Robert.Wall purchased the FTDI LC231X it should arrive in 2 or 3 business day. About the other things you mentioned I’ll verify what I have.