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Topic: Current Transformer (Read 9147 times) previous topic - next topic

brunokc

Hallo

how do i use this Current Transformer to measure how many amps I use

would it work if I put THIS on the wires from the Current Transformer?

Hope you can help me.

wvmarle

It would be helpful if you post to the English pages.

From what I read on the sensor: it outputs 0-50 mA for a current 0-100A.

The second is a current sensor, measuring up to 20A. It doesn't make sense to try and measure 50 mA with a 20A sensor. That's no match.

My best guess, based on the very limited info: use a resistor (100 Ohm) to convert the 0-50mA output into a 0-5V signal, which you can then read on the Arduino. Look for schematics of reading 4-20mA sensors, that's normally done with a 250 Ohm resistor, you would just replace that with 100 Ohm.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

TomGeorge

Hi,
Are you measuring AC or DC current?
What is the maximum current you will need to measure?
What is the load causing the current?

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

brunokc

Sorry for missing info.

It's to measure up to 400v 50a ac.

wvmarle

Of course AC, otherwise such a transformer wouldn't work in the first place. So the output is also AC - which means you should add a rectifier at least.
And then my transformer knowledge is too lacking to know the relationship between current and voltage when you add a load.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.


dave-in-nj

Of course AC, otherwise such a transformer wouldn't work in the first place. So the output is also AC - which means you should add a rectifier at least.
And then my transformer knowledge is too lacking to know the relationship between current and voltage when you add a load.
a CT is a clamp-on or pass through unit that develeops a realationship of current in and AC voltage out.
if you have, say 2 volts AC, you need to eleveate that to get something like 1/2 volt up to 4.5 volts.
it is still AC, but you can read that on an analog input pin.


brunokc

Thanks. I will read up on that.

I bought one of their arduino shield. However, I can not figure out the data so I can use it to enable relays when I'm making too much power.

aarg

Thanks. I will read up on that.

I bought one of their arduino shield. However, I can not figure out the data so I can use it to enable relays when I'm making too much power.

What shield?
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

dave-in-nj

What shield?
I am going out on a limb.....
guessing 'their' means open energy mon
and the only Arduino shield I know they have is this
https://shop.openenergymonitor.com/emontx-arduino-shield-smt/

brunokc

https://shop.openenergymonitor.com/emontx-arduino-shield-smt/

dave-in-nj

Thanks. I will read up on that.

I bought one of their arduino shield. However, I can not figure out the data so I can use it to enable relays when I'm making too much power.

OK, so one of the rules of all internet forums, is you start with a simple explanation and links to details.
I have this schield :
https://shop.openenergymonitor.com/emontx-arduino-shield-smt/
and tried to make it work, but cannot read the amps.....
or , I can read amps, but now want to have relays open and close when the amps get too high.

my device reads 0 amps when not working, and it rads 3.2 amps when running full.


I want to turn the relay on at 2.4 amps.

[ I read and understand the  how to use this forum and understand what a 'code tag' is ]

here is my code  [in code tags ]

wvmarle

#12
Nov 23, 2017, 03:12 pm Last Edit: Nov 23, 2017, 03:12 pm by wvmarle
I think OP is not interested in the waveform so it may be easier to put the signal through a rectifier and then add a capacitor (10-100μF) for a constant output voltage. Then it doesn't matter so much when exactly you make the measurement. Like this:


After that it's a matter of calibration.
I assume linear relation between output current and the measured current.

Then to switch the relay based on the current, very simple:

Code: [Select]

void loop() {
  reading = analogRead(A0);
  if (reading > 500) {
    digitalWrite(RELAY_PIN, HIGH);
  }
  else {
    digitalWrite(RELAY_PIN, LOW);
  }
}


This way you switch the relay on and off at about 200A.

0A should give a reading of 0, 400A should give a reading of about 1023. Burden resistor value could be lowered a bit to keep maximum voltage just under 5V - safer, without losing too much accuracy. Also no hysteresis in this code: if current is 200A the relay may start switching a lot as readings are not perfect.

Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

brunokc

I think OP is not interested in the waveform so it may be easier to put the signal through a rectifier and then add a capacitor (10-100μF) for a constant output voltage. Then it doesn't matter so much when exactly you make the measurement. Like this:


After that it's a matter of calibration.
I assume linear relation between output current and the measured current.

Then to switch the relay based on the current, very simple:

Code: [Select]

void loop() {
  reading = analogRead(A0);
  if (reading > 500) {
    digitalWrite(RELAY_PIN, HIGH);
  }
  else {
    digitalWrite(RELAY_PIN, LOW);
  }
}


This way you switch the relay on and off at about 200A.

0A should give a reading of 0, 400A should give a reading of about 1023. Burden resistor value could be lowered a bit to keep maximum voltage just under 5V - safer, without losing too much accuracy. Also no hysteresis in this code: if current is 200A the relay may start switching a lot as readings are not perfect.


This looks great, but my current transformer only goes up to 100A, and I only need measure up to 50A max.
Is there a way to scale it down to 50A max

Juraj

@wvmarle the OP has the openenergy shield that does it everything. he just doesn't know how to use it

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