Trying to measure milliamps.

Other Hardware Sensors
1

I brought a pack of 5, 30 amp model, ACS712 modules for monitoring current draw for a solar panel project . I am looking for measuring a current draw of 250mA

Without even hooking into the arduino and just measuring the Vout pin of the module, a current in the range of 0-150mA will not do that much change to the Vout (it holds at 2.51) ,in fact all I get in the voltmeter is 10mV of a change. I am coming to the conclusion that this module is only useful for current in the Amp range instead of milliamps.

What I'm looking for is a module caple of measuring down to 10mA.

Sidenote:

Ive also noted that I only get the 0 current voltage of 2.5 volts if the grounds are tied together...meaning that the circuit that passes through the hall affect sensor must also have a ground connected into the arduino.

If I don't do this the Vout drops from 2.5 to 100mV as if it were to indicate a negative current flow.

2

this module is only useful for current in the Amp range instead of milliamps.

Correct.

To measure small currents you can use a resistor and the Arduino ADC with the 1.1V internal reference. A 2.0 Ohm resistor in the solar panel ground lead will lead to a full scale (1023) reading of about 550 mA.

For 10 mA resolution, you could go as low as 0.1 Ohm.

3

Thanks for you reply.

Though I must understand that using the 1.1volt reference means then that anything at 1.1volt will be considered 1023, correct?

If so I understand then I will also have to recalibrate the voltage dividers reading voltages of the solar panel and battery.

Though it isn't clear to me could I call the analogreference for a specfic port or does it affect all of them?

4

Also correct. All the ADC pins use the same analog reference, but you can switch back and forth between references.

I suggested to use the 1.1V internal reference for measuring the current because that allows you to use a low value resistor as the current sensor. You can certainly use the 5V reference, but the resolution will be poorer.

With a 2 Ohm resistor, 250 mA would produce a voltage drop of 0.5V, or an ADC reading of about 100 using the 5V reference (2.5 mA per step).

5

AFAIK Arduino ground has to connect to the solar side of the shunt if you want a positive voltage on the analogue input. Not sure about the implications if you charge a battery and power the Arduino with that when the sun goes down. There will now be a negative voltage on the analogue input.
Leo..