Hello, I have a problem with the ACS712 current sensor.
I created a smart power tap and I want to calculate the current consumption with the current sensor.
I found a lot of code on Internet and this is what I use :
// Libraries required for Wifi connection
#include <Wire.h>
#include <UnoWiFiDevEd.h>
float amplitude_current;
float effective_value;
float effective_voltage = 110; // Set voltage to 230V (Europe) or 110V (US)
float effective_power;
float zero_sensor;
float power;
void setup() { //Initialization loop
pinMode(13,OUTPUT); //Signals to the Arduino that connection 13 must be able to send current
Wifi.begin(); //Initializes the network settings of the Wi-Fi library
Wifi.println("Web Server is ok"); //Display when the web server has started
zero_sensor = getSensorValue(A0);
Serial.begin(9600);
}
void loop() { //Infinite loop
while(Wifi.available()) { //as long as wifi reading is available
readUrl(Wifi); //call to the readUrl function
}
delay(50); //50ms pause
// Perform power measurement
float sensor_value = getSensorValue(A0);
// Convert to current
amplitude_current = (float)(sensor_value-zero_sensor)/1024*5/100*1000000;
effective_value = amplitude_current/1.414;
effective_power = abs(effective_value*effective_voltage/1000);
Serial.print("\n amplitude current = ");
Serial.print(amplitude_current,2);
Serial.print("\t effective_value = ");
Serial.print(effective_value,2);
Serial.print("\t Power (W) = ");
Serial.print(effective_power,2);
delay(1000);
}
// Get the reading from the current sensor
float getSensorValue(int pin)
{
int sensorValue;
float avgSensor = 0;
int nb_measurements = 1000;
for (int i = 0; i < nb_measurements; i++) {
sensorValue = analogRead(pin);
avgSensor = avgSensor + float(sensorValue);
}
avgSensor = avgSensor/float(nb_measurements);
return avgSensor;
}
However, I got strange values. For example, whatever the device connected to the SPT, the power is always approximatively :
amplitude current = -1.76 effective_value = -1.24 Power (W) = 0.14
amplitude current = 0.24 effective_value = 0.17 Power (W) = 0.02
amplitude current = -1.61 effective_value = -1.14 Power (W) = 0.13
amplitude current = -59.91 effective_value = -42.37 Power (W) = 4.66
amplitude current = -56.54 effective_value = -39.99 Power (W) = 4.40
amplitude current = -52.10 effective_value = -36.85 Power (W) = 4.05
amplitude current = -69.43 effective_value = -49.10 Power (W) = 5.40
amplitude current = -69.34 effective_value = -49.03 Power (W) = 5.39
amplitude current = -53.32 effective_value = -37.71 Power (W) = 4.15
amplitude current = -50.34 effective_value = -35.60 Power (W) = 3.92
amplitude current = -55.76 effective_value = -39.44 Power (W) = 4.34
amplitude current = -41.60 effective_value = -29.42 Power (W) = 3.24
amplitude current = -58.25 effective_value = -41.20 Power (W) = 4.53
amplitude current = -55.13 effective_value = -38.99 Power (W) = 4.29
amplitude current = -59.18 effective_value = -41.85 Power (W) = 4.60
amplitude current = -57.23 effective_value = -40.47 Power (W) = 4.45
Could someone help me pls. You can find attached the schematich of my project. Thanks.
What is IP- connected to? It needs to be connected to something. Also, note that you are measuring AC current (redundant - I know, lol) and you will get all sorts of values for current (both positive and negative).
You calculate the voltage difference from the zero point in volts, then divide by 10000 in
an inefficient way. You should be dividing by the sensor sensitivity to get the current. The
sensitivity of the 20A device is 0.1V/A:
amplitude_current = (float)(sensor_value-zero_sensor)/1024*5/0.1; // current in amps
Hello and thanks for reply,
here is my new program :
// Libraries required for Wifi connection
#include <Wire.h>
#include <UnoWiFiDevEd.h>
void setup() { //Initialization loop
pinMode(13,OUTPUT); //Signals to the Arduino that connection 13 must be able to send current
Wifi.begin(); //Initializes the network settings of the Wi-Fi library
Wifi.println("Web Server is ok"); //Display when the web server has started
Serial.begin(9600);
}
void loop() { //Infinite loop
/*
while(Wifi.available()) { //as long as wifi reading is available
readUrl(Wifi); //call to the readUrl function
}*/
delay(50); //50ms pause
// Perform power measurement
float amplitude_current = getCurrentValue(A0);
Serial.print("\n amplitude current = ");
Serial.print(amplitude_current,2);
delay(50);
}
float getCurrentValue(int pin) {
int absVal;
long int absSum = 0;
float current;
for ( int i = 0 ; i < 20000 ; i++ ) {
absVal = analogRead(pin);
absVal = ( absVal - 512 );
absVal = ( ( absVal >= 0 ) ? ( absVal ) : ( -absVal ) );
absSum = ( absSum + absVal );
delayMicroseconds(50);
}
current = ( (float)absSum );
current = ( current / 20000.0 ); // Division par le nombre d'éléments
current = ( ( current * 5.0 ) / 1024.0 ); // Conversion en volt (ADC 10bits=1024pts, ref 5.0V)
current = ( current * 10.0 ); // Conversion en ampères (ACS712-20A: 100mV/A=10A/V)
return current;
}
However, I still have incorrect values and I dont understand why.
I know my values are incorrect because I have a wattmeter with me.
For example, when my pc is connected to the device I should have approximatively:
100V | 0.30~0.50Amp | ~30Watt
Could someone help me pls ? Thanks
Mouk:
However, I still have incorrect values and I dont understand why.
I'm going to say this ... one ... last ... time: It's because you are measuring AC current
Your code is for DC current and DC power ONLY. In order to calculate real power in watts for an AC circuit, you need to use the following formulas (in order from top to bottom):
Vrms = Vpeak /sqrt(2);
Irms = Ipeak/sqrt(2);
S = Vrms * Irms;
pf = cos(360fdeltaT)
P = S * pf
Where Vpeak is the peak voltage, Ipeak is the peak current, Vrms is the RMS voltage, Irms is the RMS current, f is the frequency (60Hz), deltaT is the time difference (in seconds) between zero crossing of the voltage and the current, P is real power in watts, S is apparent power in VA, and pf is the power factor.
Lastly, you need to double check these power ratings again:
Mouk:
For example, when my pc is connected to the device I should have approximatively:
100V | 0.30~0.50Amp | ~30Watt
Are they DC values or AC RMS values?
I'd also double check the tutorials you used to see what units the code provides the resulting current in. Is it A, mA, nA, etc?
