# Integrating CT with Arduino

Hi,
I have recently bought CT with the following specs:
250A primary and 5A & Turns ratio is 50(250/5)secondary VA 3.75 and CL:1.
I have chosen a burden resistor of 0.33Ohm in order to keep the Voltage below the Arduino ADC 5V.
I have followed the code from this example:
https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/how-to-build-an-arduino-energy-monitor-measuring-current-only
I'm trying to measure current consumption of 60W Incandescent bulb. Live wire from the AC is fed to bulb via CT.
But when I run the code, with or Without turning on the bulb I'm reading the same value of Irms.
The below are the some of readings:

9898.39
rms 43.04
10142.66
rms 44.10
9920.48
rms 43.13
9632.31
rms 41.88
9290.67
rms 40.39
9955.50
rms 43.28
9515.76
rms 41.37
9565.85
rms 41.59
9925.27
rms 43.15

Even with the analogRead i didn't see much of change it was varying between 300-800.
I was expecting from 0-1024 variation.

Ca someone guide me?

Post a schematic diagram (hand drawn, not Fritzing). Image guide
Post the code, using code tags. See "How to use this forum".

This is a good reference design: Learn | OpenEnergyMonitor

Hello lakshmi123,
Forgive me if I get this wrong as I have never used a current transformer, but does '250A primary' mean that the CT is rated to carry up to 250A by any chance?

Assuming it does, then consider that a 60W lamp at 230V draws 1/4 of an amp, which is 1/1000 of the full range of the CT, I think you are lucky to see any variation in the output of an A2D converter with a range up to 1023.

lakshmi123:
Hi,
I have recently bought CT with the following specs:
250A primary and 5A & Turns ratio is 50(250/5)secondary VA 3.75 and CL:1.
I have chosen a burden resistor of 0.33Ohm in order to keep the Voltage below the Arduino ADC 5V.

0.33 ohms and 10W, presumably? This must be a large transformer if it handles that power.

But the spec says 3.75VA, so your burden resistor is too large for full scale use. 0.1ohm would
dissipate 2.5W at full scale, more sensible for this CT.

I have followed the code from this example:
Learn | OpenEnergyMonitor
I'm trying to measure current consumption of 60W Incandescent bulb. Live wire from the AC is fed to bulb via CT.
But when I run the code, with or Without turning on the bulb I'm reading the same value of Irms.
The below are the some of readings:

9898.39
rms 43.04
10142.66
rms 44.10
9920.48
rms 43.13
9632.31
rms 41.88
9290.67
rms 40.39
9955.50
rms 43.28
9515.76
rms 41.37
9565.85
rms 41.59
9925.27
rms 43.15

Even with the analogRead i didn't see much of change it was varying between 300-800.
I was expecting from 0-1024 variation.

Ca someone guide me?

Those values make no sense, I'd expect a constant output value as the current is such a tiny fraction of
full-scale.

jremington:
Post a schematic diagram (hand drawn, not Fritzing). Image guide
Post the code, using code tags. See "How to use this forum".

This is a good reference design: Learn | OpenEnergyMonitor

yes I used the same circuit and same code.

MarkT:
0.33 ohms and 10W, presumably? This must be a large transformer if it handles that power.

But the spec says 3.75VA, so your burden resistor is too large for full scale use. 0.1ohm would
dissipate 2.5W at full scale, more sensible for this CT.Those values make no sense, I'd expect a constant output value as the current is such a tiny fraction of
full-scale.

Yeah, I agree with you. But in my case, Primary current will never go above 100A so meaning that Secondary current will be 2A VA: [22][0.33]= 1.32W well within the range rated VA. So the value of 0.33 Ohm should be fine I guess.
Yes I was expecting a constant output value. what could be the reason for this behavior?

Yes I used the same circuit and same code.

That may be so, but without a schematic of your wiring (hand drawn is fine) we don't know how you wired it up. A photo of your project is also helpful.

PerryBebbington:
That may be so, but without a schematic of your wiring (hand drawn is fine) we don't know how you wired it up. A photo of your project is also helpful.

I'll attach the picture of wiring diagram on Tuesday since we are off till Monday.

It sounds like you don't have a measuring CT, but the sort used to drive relays and trips for protection.

A ratio more like 1000:1 is common for measuring, and the CT will be much smaller.

jremington:
Post a schematic diagram (hand drawn, not Fritzing). Image guide
Post the code, using code tags. See "How to use this forum".

This is a good reference design: Learn | OpenEnergyMonitor

Since image size is crossing 2048KB I'm attaching the google drive link below FYR,
Line wire(red) is passed through the CT primary for measuring current.
Below are the corresponding reading from the Serial Monitor.
When I turn on the Bulb,Irms goes below 3(2.92,2.90,2.89,2.86).
What these number indicates, How do I calculate the current?
Another strange behaviour is that when I try to read the analog A1 separately it doesn't change even when I turn the bulb ON.

748.17 3.25
740.15 3.22
888.88 3.86
761.11 3.31
749.38 3.26
755.36 3.28
763.52 3.32
671.79 2.92
667.88 2.90
666.79 2.90
672.28 2.92
665.46 2.89
657.65 2.86
656.93 2.86
665.23 2.89
745.97 3.24
738.97 3.21
744.52 3.24
719.29 3.13
662.76 2.88
655.66 2.85
661.96 2.88
673.59 2.93
672.08 2.92
666.68 2.90

MarkT:
It sounds like you don't have a measuring CT, but the sort used to drive relays and trips for protection.

A ratio more like 1000:1 is common for measuring, and the CT will be much smaller.

I don't think so, this looks like a measuring CT
you can have a look at the CT below drive link :
I believe CT with ratio of 2000:1/2500:1 are common.

MarkT:
0.33 ohms and 10W, presumably? This must be a large transformer if it handles that power.

But the spec says 3.75VA, so your burden resistor is too large for full scale use. 0.1ohm would
dissipate 2.5W at full scale, more sensible for this CT.Those values make no sense, I'd expect a constant output value as the current is such a tiny fraction of
full-scale.

Yeah, there was one mistake in breadboard connection of the ground.
Now the values look like these:
Without turning on
748.17 3.25
740.15 3.22
888.88 3.86
761.11 3.31
749.38 3.26
755.36 3.28
763.52 3.32
745.97 3.24
738.97 3.21
744.52 3.24
719.29 3.13

With Bulb ON
671.79 2.92
667.88 2.90
666.79 2.90
672.28 2.92
665.46 2.89
657.65 2.86
656.93 2.86
665.23 2.89
662.76 2.88
655.66 2.85
661.96 2.88
673.59 2.93
672.08 2.92
666.68 2.90
671.55 2.92
677.57 2.95
But How do I convert these values?

My comments are unchanged if you are using the 50:1 ratio CT - its way too insensitive to measure 60W.

MarkT:
My comments are unchanged if you are using the 50:1 ratio CT - its way too insensitive to measure 60W.

Okay. I'll change the CT and revert the result in 2 Days.

MarkT:
My comments are unchanged if you are using the 50:1 ratio CT - its way too insensitive to measure 60W.

I've changed CT with the Turns ratio 2500:1,100A Rating.
(ELECTROHMS | CT1273-A1-Rc | Energy Metering | Current Transformers Product)
As per the formulae, the chosen burden values are 43Ohm.
When the Bulb(60W,230V) is off I'm reading the value of 2.04-2.08. When the Bulb is turned ON, value varies in b/w 2.08-2.12.
Should I try with the Higher load?

Have you checked the output voltage with a multimeter? Remember the burden resistor must always be in circuit with a CT, best to permanently wire it in.

100A / 2500 = 40mA, 40mA x 43 ohms = 1.72V rms, which should be good for 100A,
but you are measuring a fraction of an amp, so the output will be a few mV.

What full scale reading do you want?

With no current the output of the CT should be flatlining without any change, perhaps flickering by one count. If not then noise is getting into your system (long wires?)

MarkT:
Have you checked the output voltage with a multimeter? Remember the burden resistor must always be in circuit with a CT, best to permanently wire it in.

100A / 2500 = 40mA, 40mA x 43 ohms = 1.72V rms, which should be good for 100A,
but you are measuring a fraction of an amp, so the output will be a few mV.

What full-scale reading do you want?

With no current the output of the CT should be flatlining without any change, perhaps flickering by one count. If not then noise is getting into your system (long wires?)

I haven't tried with the multimeter.
Yes, the Burden resistor is placed on the breadboard.
It's not long wire hardly 5cm from the CT to the breadboard.

Here's the code with an example which I tried yesterday

#include "EmonLib.h"
// Include Emon Library
EnergyMonitor emon1;
// Create an instance
int val=0;
void setup()
{
Serial.begin(9600);

emon1.current(1, 111.1); // Current: input pin, calibration.
}

void loop()
{
Serial.println(val);
delay(500);
double Irms = emon1.calcIrms(1480); // Calculate Irms only
Serial.print(Irms*230.0); // Apparent power
Serial.print(" ");
Serial.println(Irms); // Irms
delay(500);
}

I'm trying to test with the 60W Incandescent Bulb(230V).
When I run the code with Bulb turned off I'm getting these values:

A1:518
90.22 0.39
518
85.24 0.37
519
85.34 0.37
519
84.25 0.37
518
84.72 0.37
518
85.34 0.37

With the Bulb turned ON:

517
182.35 0.79
519
166.67 0.72
519
166.59 0.72
520
167.40 0.73
518
165.27 0.72
517
166.05 0.72
517
167.56 0.73
519
167.18 0.73

@lakshmi123

DO NOT CROSS POST other post deleted.

Bob.

ballscrewbob:
@lakshmi123

DO NOT CROSS POST other post deleted.