Hello everyone

I'm looking for an accurate current sensor which works with Arduino, I need it to monitor the current of a LiFePO4 battery charger.
I've tried working with a 5A ACS-712 but it's not really working maybe because the current I'm working with is quite low 120mA.
Furthermore, it's supposed to have a 2.5V AC offset however without any current going through the sensor the Vout has an output of 2.56V and could change slighty. This sensor outputs 185mv on top of the offset per 1A. So ideally with a current of 1A the output should be 2.685V however since I'm measuring a small current any inaccuracy could affect my current output majorly.....
Is there any better sensor module that you could recommend.... or maybe a different method to measure the current altogether.... I saw a INA219 does anyone know if they are any good?

Thank you

 

You could simply use a resistor and measure the current by measuring the voltage across the resistor. As you probably won't want to drop much voltage then a low value resistance followed by an amplifier would be the way to go.

 

As suggested by AlberHall using a shunt resistor is the best method.

You can use the above circuit. Neglecting the Resistors R1 and R2 which is used for measuring Voltage. Here the current flowing through the resistor is amplified using an Op-Amp and is feeded to a Micro controller like Arduino.

More information and Source is available at : https://circuitdigest.com/microcontroller-projects/12v-battery-charger-circuit-diagram-using-lm317

 

You could simply use a resistor and measure the current by measuring the voltage across the resistor. As you probably won't want to drop much voltage then a low value resistance followed by an amplifier would be the way to go.

yes, I've thought about that...... a very low resistance actually (preferrably somewhere in the order of milliohms) so that when the battery discharges the resistor doesn't consume too much battery.... I've seen some shunt resistors however they appear to be quite large in size.... which is quite troublesome....

 

Furthermore, it's supposed to have a 2.5V AC offset however without any current going through the sensor the Vout has an output of 2.56V and could change slighty.

The sensor has a ratiometric output. How accurate is your 5V supply voltage? If your supply to the device was 5.12V, then 2.56V output at zero current would be the correct output.

 

yes, I've thought about that...... a very low resistance actually (preferrably somewhere in the order of milliohms) so that when the battery discharges the resistor doesn't consume too much battery.... I've seen some shunt resistors however they appear to be quite large in size.... which is quite troublesome....

Okay lets do the Math. The maximum current you wanna measure should be around 200mA lets assume it to be 250mA for saftey reasons.


So you have a lot of options here. You can simply use a 2W resistor that is commonly available. And its resistor value can be anywhere between 0.5 ohms to 2 ohms considering the voltage drop across the resistor.

Speaking about consuming battery lets say you select the 1ohm 2W resistor. Then the voltage drop across it will be 0.25V at 250mA which is think is pretty much reasonable for a Lipo Battery.

Also I am sure that its hard to get your 5A ACS712 work for you since your current value is very less. You might try with some software filters and post here if you had any luck with it.

 

The sensor has a ratiometric output. How accurate is your 5V supply voltage? If your supply to the device was 5.12V, then 2.56V output at zero current would be the correct output.

Hmmm that's something to take note of, thank you.

 

Okay lets do the Math. The maximum current you wanna measure should be around 200mA lets assume it to be 250mA for saftey reasons.
View attachment 131746

So you have a lot of options here. You can simply use a 2W resistor that is commonly available. And its resistor value can be anywhere between 0.5 ohms to 2 ohms considering the voltage drop across the resistor.

Speaking about consuming battery lets say you select the 1ohm 2W resistor. Then the voltage drop across it will be 0.25V at 250mA which is think is pretty much reasonable for a Lipo Battery.

Also I am sure that its hard to get your 5A ACS712 work for you since your current value is very less. You might try with some software filters and post here if you had any luck with it.

Yeah, you're right that should work pretty well!!
Thanks a lot sir