New and Not certain the readings i see is of my cable

hello guys good to be joining the community.
please i have recently gotten an emmon tx and have linked it up with the raspberrypi base station and can see some readings on the emoncms. i do have a strong feeling that the readings which appears on “emontx3cm15” section is not the reading of the appliance which i am monitoring. Also all reading on “emonpi” section is always null.

please any advice would be greatly appreciated. also i have attached some pictures i believe will help in explaining my problem better.

also please i would like your opinion on this connection

Welcome, @Obiefuna_Obidike to the OEM forum.

Why? Do the readings change when you turn your appliance on or off, or do they not change? Or are the numbers not what you expect? What are CT1 & CT2 monitoring? Please remember, all we know about what you are trying to do is what you write and what we can see in the pictures.

Looking at the bottom photo, it looks as if you have a primary winding of 3 turns for your c.t. That being the case, and unless you have changed the calibration of your emonTx, or somewhere in emonCMS divided by three (or multiplied by 0.333), you will be reading three times the actual current that your appliance takes.

Also, the c.t. you are using (if it is the 100 A version from our Shop) is not specified for accuracy below 10 A. In your case you are measuring the current 3 times, which is good, so you’ve reduced that to 3.3A, or about 800 W. If whatever you are trying to measure has a rating significantly less than this, don’t expect accuracy.

Do you have an emonPi (in the ribbed aluminium case, with sockets for 2 c.t’s and a.c. adapter, and LCD display - look on the Shop pages if you are unsure), or an emonBase as you say (a Raspberry Pi with a RFM69Pi receiver module)? If the latter, then you won’t get anything from the emonPi because you don’t have one!

All I can see is a plastic box and a lot of crimp connectors. I can’t see what’s outside or what it’s doing. Should I have guessed that one side goes to a mains plug and the other to your appliance? Remember what I wrote above about telling us what you are doing, or trying to do.

I think you’ve made this so that the single wire going through the c.t. is safe. This is very good, but I am a bit concerned about the thickness of the wire. The connectors (if they are IEC “kettle” ones) could be rated at 16 A, and while it’s difficult to tell the exact wire size, it does look a bit thin for 16 A. I’d especially worry about the 3 turns, because that counts as “bunched” wiring, because each turn will heat the adjacent one and prevent the heat from getting away, so the wire size needs to be greater to reduce the resistance, hence the heating effect.

Hi Robert,
thanks for taking the time to assist.
Ans.1, yes, the reading fluctuates on its regardless of the appliance(a TV.) being on of off. even with not knowing what to expect i feel the numbers are not correct.

Ans.2, I only had the CT2 plugged in to monitor a Television.

Ans.3, yes, with the little knowledge i have i am aware of the effect of the winding

Ans.4, I have an emonBase (a Raspberry Pi with a RFM69Pi receiver module)

Ans.5, yes you are right about the connection one gets supply from the mains and the other is where the Tv is connected to.
supply from mains for appliance

Connection to the mains


hope this helps explain my issue better.

  1. You should expect small fluctuations - the brightness of the picture on the TV screen, or the loudness of the sound, will affect the power the TV consumes.

  2. You can look at the label on the back of the TV to see how much power it will consume.
    Your emonCMS is showing 98 W for your TV. It is -98 W because the c.t. is facing the wrong way on the cable. You can either turn it around, or you can multiply by -1 inside emonCMS, on the Inputs page. Look at the Guide for more detail. 98 W sounds about right for a modern TV.

You photo of the TV shows the Raspberry Pi starting up. That is normal. You don’t normally need to see that, we expect the Raspberry Pi to not have a display. All your useful information will appear in emonCMS, either as Graphs or Dashboards.

As you have it with a 3-turns coils, your c.t. will read up to 33 A (8 kW), but the wire and the cable you have used is nowhere near capable of that. You could easily increase the number of primary turns up to 10, giving you a maximum current of 10 A, and then multiply the power in emonCMS by 0.1 to bring you back to the correct value, or -0.1 to make it positive). You should use 1.5 mm² wire for 10 A, because there will be 10 wires bunched together.

I expect to see a small “power” even when there is zero current. Here is what an emonTx V3.4 not in its case shows, with an a.c. adapter and 2 c.t’s plugged in:

21:38:52.906 -> AC present 
21:38:52.906 -> MSG:1,Vrms:238.14,P1:12,P2:2,E1:0,E2:0,T1:18.25,pulse:0
21:39:02.830 -> MSG:2,Vrms:238.09,P1:11,P2:2,E1:0,E2:0,T1:18.25,pulse:0
21:39:12.790 -> MSG:3,Vrms:238.20,P1:12,P2:2,E1:0,E2:0,T1:18.25,pulse:0
21:39:22.749 -> MSG:4,Vrms:238.25,P1:11,P2:2,E1:0,E2:0,T1:18.25,pulse:0
21:39:32.708 -> MSG:5,Vrms:238.32,P1:12,P2:2,E1:0,E2:0,T1:18.25,pulse:0
21:39:42.631 -> MSG:6,Vrms:238.37,P1:12,P2:2,E1:0,E2:0,T1:18.25,pulse:0

This is the Continuous Monitoring V2.3 sketch, direct output (not via emonCMS).
If I was using a 10-turn primary winding for the c.t., and then dividing by 10 in emonCMS, the powers would be P1 = 1.2 W and P2 = 0.2 W. This power is due to electrical ‘noise’ inside the emonTx, and there’s little that you can do about it. It is after all only about 12 W in 24 kW for me, or about 0.05% of the maximum reading.

Thank again Robert, i probably haven’t understood the system yet.
i took a screenshot of my emonCms readings at various state of the appliance.

  1. the tv was on standby mode with only the red power led light on.

  2. tv was turned on and screenshot was taken after 15 sec

  3. Tv was powered off and back to standby mode and screenshot was taken after 15 sec

i was told i can only post 3 media in a post as a new user

  1. tv connection was disconnected from mains and screenshot was taken after 15 sec

  2. i have added a screen shoot of my emonhub log

All those look reasonable to me. If you have not calibrated your emonTx, and you are not dividing by 3 in emonCMS, then it shows your TV is using 106 ÷ 3 = 35 W when it is on. This is probably low, but it is not unreasonably inaccurate as the maximum it will read is 24 kW (actually 8 kW as you have the 3-turns primary winding for your c.t.).

Your emonTx reports the average power over the previous 10 s every 10 s, so if the TV takes 35 W, and you turn it on half way through the 10 s reporting interval, it will read 0, 17, 35, 35, etc. If you turn it off 2/3 of the way through the reporting interval, it will read 35, 23, 0, 0, etc.
The emonTx’s reporting period is not linked to when emonCMS refreshes the page. When the value on the Inputs page is refreshed, it is already old by that number of seconds/minutes.

Thanks for explaining, i am gradually coming to grasp.
please where can i find the “legends” of emonCMS so i can beter understand the parameters.

also where i can i go to learn more on calibration of my ct sensor.

I’m not sure what you mean. If you scroll to the top of the page, you’ll see a link to “Guide”. This explains quite a lot about emonCMS. It will probably help you to know that the emonPi is essentially a two-current input, cut down version of your emonTx and your Raspberry Pi inside a nice aluminium box. So a lot of what is written about the “emon” (Energy MONitor) part of the emonPi also applies to the emonTx, and a lot of what is written for and about the emonTx also applies to the emon part of the emonPi. And the software you installed on your RPi is identical to that you install in the emonPi.

For this, go to the ‘Learn’ section. The page you want is not completely up to date, but I think you will be able to follow it. It is under “Current & Voltage”.

thanks again Robert

Hi Robert, once again. i do need some assistance.
i see there is a way to have the reading from emoncms sent to nodered.
my questions are:

  1. can i have the raspberry pi os (to view the raspberry pi desktop) and the emonSD on the same SD and raspberry pi?
  2. can i have nodered running on my emonbase(raspberry pi + RFM69Pi receiver)?
  3. can you guide me through sending data from emoncms to the emon node on nodered?

Also do i have to create a new topic for this or edit this topic?

I’m afraid I cannot help you with that. I know nothing about Nodered. You’ll need to wait for somebody who knows about it to respond.

I believe, though I might be wrong, that Nodered is already installed in the emonCMS SD Card image.

In theory yes, but I’ve not done it. I can’t recommend it though, as the desktop GUI is a very big bit of software that uses a lot of resources. Putting data into the databases is a time critical operation, running a browser for NR is going to impact that. Unless maybe you’re using a RPi4 with 4GB or 8B of RAM.

Yes, you can have NodeRed running on the same Pi that runs your EmonCMS, I’ve done that for about 8 years on RPi2. Go to NodeRed’s website and use the BASH command line install, don’t use the version of NR that’s available from the RPi OS repo, that version is way too old.

There are a couple of ways, you can either add the “node-red-node-emoncms” module to NR from the Pallet Manager and use that, it gives you a couple of new nodes that can send data directly TO EmonCMS or receive data FROM EmonCMS, both in realtime.
OR you can use MQTT, this is natively supported by both NR and EmonCMS. EmonHub can retransmit incoming data to MQTT where you have a subscriber node that injects the data whenever EmonHUB sends it. You can also send MQTT data from NR straight into EmonHub.
Ten minutes of playing and you’ll understand what I mean.

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