OpenEnergyMonitor Community

CT Sensor, BLYNK, wrong values when measuring three phases feed

Hey guys.

I’m developing something around my Wemos D1 Mini Pro, a TT-100-SD, blynk, and the Emonlib library.

I reached a point where my arduino could mesure out of one phase (2 phases, one ground, 230v) continously and transmit thoses datas to blynk and make some charts… That was for debugging, getting used to code etc…

When I clamped my CT sensor to the machine I’d like to monitor (3 feed phases, 400v). All my values are really off, so I changed the calibration but even tho I get the nice value while working (it’s stable but not showing the reals values, ie : when the machine is punching metal I should get a peak of 80 Amps, but it stays really still around 36 amps), when my machine is off and supposed to show 0 amps, I’ve only lost 2-3 amps on my mesures so it gives me something around 33 amps.

I’ve tried many formula, getting the apparent power, multiplying with Square(3)*Voltage * 3 phases … But nothing seems to work.

I did read it was possible on three phases assuming they are correctly balanced (they are) to mesure only one phases with a Amps meter (non-intrusive) and make mesurements.

If anyone knows what my problem is, that would be awesome !

// Premiere partie du code qui définie la base du code. Permet d'inclure les librairies, définir les noms etc..)

#define BLYNK_PRINT Serial // Permet d'écrire ce qu'il se passe sur le monitor
#define BLYNK_DEBUG_ALL Serial

#include "EmonLib.h" // Librairie de mesure de courant
EnergyMonitor emon1; // Creation 'une instance

#include <ESP8266WiFi.h> // Lib Wifi
char ssid[] = "BLINK";
char pass[] = "12345678";               

#include <BlynkSimpleEsp8266.h> // Lib Blynk
char auth[] = "xxxxxxxx";//yourauthtoken
BlynkTimer timer; // Fait appel a la librairie Blynk pour lui faire comprendre qu'un timer sera ajouté dans le code

#include <ESP8266mDNS.h>
#include <WiFiUdp.h>
#include <ArduinoOTA.h>

//Début de la fonction sendSensor

void sendSensor()
  double Irms = emon1.calcIrms(1480); 
Blynk.virtualWrite(V0, ((Irms*400)/(1.732*400)*3)); // Lib Blynk, écrit sur le pin virtuel V0 la valeur emon1.calcIrms(1480)
if (emon1.calcIrms(1480) > 1) {
  Blynk.virtualWrite(V2, 255);
  Blynk.virtualWrite(V1, 0);
else if (emon1.calcIrms(1480) < 1) {
  Blynk.virtualWrite(V1, 255);
  Blynk.virtualWrite(V2, 0);

// Début de la fonction Setup, qui ne se réalise qu'une seule fois (sauf si appel...)

void setup()
  Serial.begin(9600); // Ecris sur le monitor en baud 9600
  Blynk.begin(auth, ssid, pass, "", 8080); // Lib blynk, connexion Token,wifi,mdp, ip serveur blynk, port 8080 ou 81 à modifier
  emon1.current(0, 11.755);             // Courant : Pin input a savoir Analogique0 = 0, calibration (à taton, nécessaire de lire la librairie pour comprendre si calcul possible).
  timer.setInterval(1000L, sendSensor); // timer lancant en boucle tout les "xL" en ms, la fonction sendSensor
   ArduinoOTA.setPassword((const char *)"123");
    ArduinoOTA.onStart([]() {
  ArduinoOTA.onEnd([]() {
  ArduinoOTA.onProgress([](unsigned int progress, unsigned int total) {
    Serial.printf("Progress: %u%%\r", (progress / (total / 100)));
  ArduinoOTA.onError([](ota_error_t error) {
    Serial.printf("Error[%u]: ", error);
    if (error == OTA_AUTH_ERROR) Serial.println("Auth Failed");
    else if (error == OTA_BEGIN_ERROR) Serial.println("Begin Failed");
    else if (error == OTA_CONNECT_ERROR) Serial.println("Connect Failed");
    else if (error == OTA_RECEIVE_ERROR) Serial.println("Receive Failed");
    else if (error == OTA_END_ERROR) Serial.println("End Failed");
  Serial.print("IP address: ");

// Début de la fonction loop, qui tourne en boucle
// Il est nécessaire d'avoir une fonction loop la plus épuré possible sous peine de latence, déconnexion, bug .......

void loop()
{; // fait appel a tout les arguments blynk; // enclenche le timer.setInterval, qui tout les "xL" active la fonction sendSensor

FYI : If I change Blynk.virtualWrite(V0, ((Irms400)/(1.732400)*3)); // for (V0, IRMS) my mesurements on 230v are perfect and perfectly responding to any amps changes

For real current, I use a Hand clamp, or a fluke logger, both are pretty precise, the fluke is clearly the most usefull as I took some date over hours.

To measure with the arduino I use :

A TT100SD, that has an arrow to know how to plug it (in the flow of the current)

The values are off, it’s not important, what’s important is that there is no spike on the mesurements, nor a lower current while the machine is off.

To be more precise, when I calibrate to have 40A for 40A, when I should get 80A spike I only get 40.6 ~ 41A and when I should get 0 ~ 5 A max I get 39.x A… It doesn’t seem to fluctuate !

Here’s the documentation for the TT100SD

Welcome, Jonathan, to the OEM forum.

My first point and question: You seem to have a pulsating load, do you know how emonLib works? The answer to that is, it samples the current and voltage for 200 ms every 10 s by default, so if your 80 A peak current happens during the 9.8 s between samples, it will not see it.

You need to change to emonLibCM - that library continuously measures, and reports the true average over the 10 s (or whatever you set) reporting period, but it was designed for an Atmel ATmega328 processor, and I don’t know whether it will run on what you have.

There must be something wrong with your hardware and your wiring. To begin, why are you decoupling the mid-point bias to +5 V instead of the GND? If there is any noise on the 5 V, then the ADC will measure it, and that is wrong.

When you have corrected that - do you see a reading when you short-circuit the c.t? If you do, it’s still electrical noise that you are measuring, not real current.

That is indeed correct.

Thank you for all the answers. I’ll check that any time soon. For the wiring I followed this tutorial


If you look carefully, the capacitor IS connected to GND there. This is why a conventional circuit diagram, properly drawn, is always better.

Look at this:

Hi ! So I should invert the C1 capacitor + from 5v pin to Gnd pin ?

NO - that will destroy the capacitor and there is a (very small) chance that it will explode.
You connect the - (minus) side of the capacitor to GND, and the + (positive, normally not marked) side of the capacitor to the junction of the two resistors (the mid-point).

You must NEVER reverse-bias an electrolytic capacitor - that is, never connect it with the applied voltage opposite to the markings.