CT interface with Arduino by using ACS712

[imranahmed]

Please let me know that I want to interface CT of 30/5A and 60/5A with arduino

but issue is that how arduino recognize which is CT connected 30/5A or 60/5A?

 

[paulfjujo]

hello,

the Amps range is defined by the shunt value installed across of AC712 device.
you will get Vcc/2 ( Vcc =power supply of the AC712) for zero Amps.
and about 1,6 or 1,8V for the range value.
so for 30A and 5V for Vcc:
2,5V +1,8V = 4,3V clockwise direction for the current
and
2,5V - 1,8V =0,7V anticlockwise direction

 

[imranahmed]

Can I connect CT output directly ACS712 input without burden resistor?

 

[Mrunal Ahirrao]

Have a look at this: http://www.instructables.com/id/How-to-Measure-AC-Current-using-Hall-Effect-Sensor/

- - - Updated - - -

And also at this: http://www.openhomeautomation.net/arduino-wifi-switch// no need to use CT if using ACS712.

 

[paulfjujo]

Hello,

Direct connection main AC wire to the ACS712 input, is a bit risky..

and it is better to use the cold wire instead the hot wire for safety reason..

If your main AC is 230V, peak value reach 1.414*230=325V ... even you measure a current,
the ACS712 input must support this max voltage
and if your arduino is linked to another device powered by main230V AC, wich contain a PI filter ,
like a serial link to a PC computer ( 0V RS232 linked to theGround of PC .so to Earth !)
you can have serious probleme of bad insulation.. up to destroy the circuit or cause human injury..

Use of a CT has the advantage of 100% insulation.



SAFETY FIRST !

 

[imranahmed]

Dear paulfjujo,

Thank you very much for good advise about safety precautions.

Dear I am using CT of rating primary=30A and secondary=5A.
I am connecting secondary of CT means 5A to ACS712.
If CT`s primary current change 0 to 30A usually secondary current change 0 to 5A.
I need conversion formula of ACS712 for displaying 0-30A.

 

[paulfjujo]

if yournominal ACS712 range is 5A, just do a proportional calculus..
ACS712 give about 180mV/amp with an DC output value centered at Vcc/2
so if you use a CT ratio 30/5 you will get 180/6=20mV / Amps
But you must transforme AC to DC average value... and calibrate with this..

or get ADC values at high speed to get peak Maxima and peak Minima
if your +Vref ADC is 5V => [Max Peak value - Min peak value] (Pts)*5000 / 1024 => result is mV
RMS value = P to P result in mV / (2 x 1,414) = RMS value in mV
then convert to Amps
RMS Amps value = RMS value(mV)/ 20 (mV/amps)

 

[Mrunal Ahirrao]

Instead you can interface current transformer directly with microcontroller, no need to use ACS712, google it...