How to calculate burdon and divider resistor value?

Hi Everyone :slight_smile:
I just want to make my own Current and Voltage monitoring system using Arduino!
I Already made one but it can only calculate Current!
So, I have This CT censor (TALEMA INDIA 51/16 AC1030) and don’t want to use those SCT-013-000 because everything will be in the box and I don’t want to hook anything to any cable!
With my current circuit I use 56Ω Burden Resistor and 100K as divider.
So I need to know how can I calculate burden resistor and dividers to work with Emonlib Library.
Here is my Current circuit:

Should I use the same resistors and values for my circuit?
also Can I use Voltage sensing value output as input in current calculation code to have better results?

Thanks a lot and have a lovely day :slight_smile:

Take a look at the ‘Learn’ section. How to bias the Arduino input, and how to calculate all the resistor values, is there.
The “quick” method is to choose a burden resistor that will give you as close to but not more than 1.6 V rms (for a 5 V Arduino) at the maximum current that you wish to measure, assuming that your c.t. is suitable, which I think it is.
Choose an isolating transformer (the a.c. adapter is one of those) that will give you 1.6 V or more at your maximum mains voltage. You then need to choose 2 resistors (R1 & R2 in the diagram in ‘Learn’) to give you as close to but not more than 1.6 V rms (for a 5 V Arduino) at your maximum mains voltage.
(Note: the magic number “1.6 V” takes into account all the normal tolerances and other factors.)
You can calculate the calibration coefficients that you should use by knowing that the coefficient is the voltage or current that will give you 1 V at the Arduino analogue input.

Thanks a lot :slight_smile:
I just calculate based on my CT sensor Datasheet which had 1000:1 turn ratio!
And I don’t want to calculate more than 30A 220v (16A is enough too because every Fuse in my home are 16A), So if my calculations are correct the value is 58Ω! and this means 56Ω is right choice :slight_smile:

Please correct me if I wrong!

So, Next Step is Divider resistors! which I do not know how can I choose! on the Learn Section its just wrote more resistance means less power consumption! this means I can use any value?
currently I use 100KΩ, if I go with 470KΩ I will have the same result?

For Voltage:
I have this AC/AC Transformer:

which has 9VAC as output and on learning section just wrote 9V is ideal voltage transformer.
So do I choose correct transformer for my project?

I appreciate because of quick answer :slight_smile:
Thanks a lot

Your c.t. gives you 30 mA at 30 A primary current, or 16 mA at 16 A. Your 56 Ω burden will therefore measure to nearly 30 A.
If you are measuring individual circuits, 16 A would be OK, being able to measure 30 A means that you will measure very small currents less accurately. The loss of accuracy may not be enough to worry about.

Divider resistors.
Those are what we call the bias resistors. OK, they divide the supply voltage, but they bias the input to half-supply voltage.
Choose whatever value you like. As you are using a mains-powered Arduino, 10 kΩ would be fine, so is 100 kΩ. It is not critical. I would not go below 10 kΩ These resistors do not affect the calibration.

That transformer is OK. Remember that the output voltage is only 9 V at full load. You are effectively using it with no load, so the voltage will be quite a lot higher - I guess between 10.5 and 11.5 V, and it is not specified. You will need to measure the voltage when you get it and then calculate the resistors.