measuring motor phase current with ACS712 30A current sensor

Hello all,

I’m having trouble with my current sensor. I have acs712 30A current sensor. And after uploading the code the serial monitor & serial plotter only shows a no and doesn’t change at all after turning on the power and the motor runs fine. I’m trying to measure switched reluctance motor phase current, but it doesn’t seem as though the sensor is recognizing the motor current (~12Amps). I also have tried 2 other codes and the same type of thing happens where the serial plotter doesn’t change values after turning on power. Im also using the ground, 5v, and A0 pins of an Arduino Uno.

 * Arduino Sketch for Allegro ACS712 Current Sensor 
 * this sensor can measure current at range of up to 30A
 * It operates with 5V
 * Please watch video instruction and explanation for this code.
 * Written by Ahmad Shamshiri on Sunday Jun 17, 2018 at 22:06 at Ajax, Ontario, Canada
 * for
 * View the video instruction at
 * This code has been downloaded from
#define VIN A0 // define the Arduino pin A0 as voltage input (V in)
const float VCC   = 5.0;// supply voltage is from 4.5 to 5.5V. Normally 5V.
const int model = 2;   // enter the model number (see below)

float cutOffLimit = 1.01;// set the current which below that value, doesn't matter. Or set 0.5

          "ACS712ELCTR-05B-T",// for model use 0
          "ACS712ELCTR-20A-T",// for model use 1
          "ACS712ELCTR-30A-T"// for model use 2  
sensitivity array is holding the sensitivy of the  ACS712
current sensors. Do not change. All values are from page 5  of data sheet          
float sensitivity[] ={
          0.185,// for ACS712ELCTR-05B-T
          0.100,// for ACS712ELCTR-20A-T
          0.066// for ACS712ELCTR-30A-T

const float QOV =   0.5 * VCC;// set quiescent Output voltage of 0.5V
float voltage;// internal variable for voltage

void setup() {
  // put your setup code here, to run once:
  pinMode(6, OUTPUT);
  pinMode(5, OUTPUT);
  // ACS712 Current Sensor 
  Serial.begin(9600);// initialize serial monitor
  Serial.println("Robojax Tutorial");
  Serial.println("ACS712 Current Sensor");

void loop() {
  // put your main code here, to run repeatedly:
 digitalWrite(6, HIGH);
 digitalWrite(5, HIGH);

  digitalWrite(6, LOW);

// ACS712 Current Sensor 
  float voltage_raw =   (5.0 / 1023.0)* analogRead(VIN);// Read the voltage from sensor
  voltage =  voltage_raw - QOV + 0.012 ;// 0.000 is a value to make voltage zero when there is no current
  float current = voltage / sensitivity[model];
  if(abs(current) > cutOffLimit ){
    Serial.print("V: ");
    Serial.println(voltage,3);// print voltage with 3 decimal places
    Serial.print("V, I: ");
    Serial.println(current,2); // print the current with 2 decimal places
    Serial.println("No Current");


I have to assume you are following the device specifications and have it hooked up correctly. From what I read " The board operates at 5V DC and the current flow through the sensor is converted to an output voltage starting at 1/2Vcc (or 2.5V) for no current flow and moves up 66mV per amp for positive current or down -66mV per amp for negative current. ".

Nowhere in the specifications do I see any mention of using the device for AC current. What have you found?


It seems you're using code for DC current to measure AC current. Leo..

Its a dc motor.

Its a dc motor.

A DC motor has two phases: ON and OFF.