AC Current Sensing using UNO

Thread Starter

y2jsh

Joined Oct 30, 2019
8
I am using a Current transformer to measure current from a source. Irrespective of the current i get knowing that i cannot give more than 5V to the Uno, i want to sense the current. I do not know how to go about it. I've thought of an approach that includes amplifying the current to a suitable value, converting to voltage and then the ac voltage to dc (or any change of order whichever is suitable). I am a college student with very little to no experience on this. So if i approach is correct, what are the components i can use that are not sensor modules, just ICs. If my approach is lengthy and if anyone knows a better way to do it, it would be of great help. Thank you.

This is the CT i am using
 

Thread Starter

y2jsh

Joined Oct 30, 2019
8
Hello,

The ACHS712X is a hall effect sensor with linear output.
At 0 A the sensor shows about ½ Vcc.

Bertus
I am getting a current of 0.25mA is all. So i will need a current amplifier to scale it up to alevel the Uno can read it accurately at right?
 

John P

Joined Oct 14, 2008
1,761
You're following the AAC tradition of treating the details of your project like a priceless secret. You said "measure current" and now you explain that the current is only 0.25mA.

AC or DC?
Is the source at a dangerous voltage?
Can you deal with this by putting a resistor in series with the current and then measuring the voltage across it?
What range does the current fluctuate through?
At what frequency?
What precision/accuracy must the measurement have?

Plus anything else that's important to someone thinking about the circuit.
 

Thread Starter

y2jsh

Joined Oct 30, 2019
8
You're following the AAC tradition of treating the details of your project like a priceless secret. You said "measure current" and now you explain that the current is only 0.25mA.

AC or DC?
Is the source at a dangerous voltage?
Can you deal with this by putting a resistor in series with the current and then measuring the voltage across it?
What range does the current fluctuate through?
At what frequency?
What precision/accuracy must the measurement have?

Plus anything else that's important to someone thinking about the circuit.
The topic reads AC current sensing :|
And I'm testing it out with just the supply we get at our homes. 230V @ 50Hz. It's a 5A to 1.25mA CT. The current reading i got was 0.25mA from a multimeter. I have to read it from a MCU for other applications. And it is part of a product that will be launched, so secrecy is a given
 

Reloadron

Joined Jan 15, 2015
4,578
I would also suggest using an Allegro Fully Integrated, Hall-Effect-Based Linear Current Sensor IC solution. The ACS 712 is being phased out but the ACS 723 line offers some nice improvements. The ACS 723 offers up plenty of current ranges for AC and DC current. It is also very easily interfaced to an Arduino or similar uC. For initial testing there are several distributors offering the ACS 723 already mounted on a breakout board. Here is an overview of the different type breakout boards and interfacing to Arduino as well as some Arduino sample code.

You can build a circuit around a CT (Current Transformer) but using a hall effect current transformer is the better way to go.

Ron
 

ronsimpson

Joined Oct 7, 2019
164
The current reading i got was 0.25mA
The data sheet for the Current Transformer is not good. In one place it said 2000:1 ratio. So if you are reading .25mA X 2000 = 0.5A. But in another spot I think it said 5A in 1.25mA out which is a ratio of 4000:1.

Normally I put a "burden" resistor across the transformer and measure the voltage but the data sheet is not clear as to resistor value.
 

dendad

Joined Feb 20, 2016
3,073
Try feeding the current transformer into a bridge rectifier then have the burden resistor as the rectifier load. Add a cap across the resistor for smoothing. That will give you a DC that the Arduino can read.
Adjust the burden resistor value so the output volts is in the range you need to measure. Arduino input protection is a must. The reverse diodes clamp the ADC input volts, and the 10K (may be a bit high) limits the current.
CurrentTransformer.jpg
Something like this.
Scale it so that the full scale reading is higher than your expected current so then you can detect an over current condition.
 
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