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

#### brunokc

##### Nov 23, 2017, 12:32 pm
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

#1
##### Nov 23, 2017, 01:09 pm
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

#2
##### Nov 23, 2017, 01:13 pm
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

#3
##### Nov 23, 2017, 01:26 pm
Sorry for missing info.

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

#### wvmarle

#4
##### Nov 23, 2017, 01:31 pm
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.

#5

#### dave-in-nj

#6
##### Nov 23, 2017, 01:37 pm
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.

#### brunokc

#7
##### Nov 23, 2017, 01:43 pm
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

#8
##### Nov 23, 2017, 01:55 pm
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

#9
##### Nov 23, 2017, 02:56 pm
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

#10
##### Nov 23, 2017, 03:00 pm
https://shop.openenergymonitor.com/emontx-arduino-shield-smt/

#### dave-in-nj

#11
##### Nov 23, 2017, 03:01 pm
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 pmLast 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

#13
##### Nov 23, 2017, 03:25 pm
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

#14
##### Nov 23, 2017, 03:28 pm
@wvmarle the OP has the openenergy shield that does it everything. he just doesn't know how to use it

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