I am using the ACS709 current sensor together with an Arduino board to measure the charge/discharge current of a large battery connected to an UPS.
I noticed a strange noise pattern in my DC measurements, which seems to be 50 Hz. I guess it must be the UPSs inverter, which draws power in such a way.
My goal is to get rid of that pattern and get reading similar to what my multimeter can measure.
I have read both the documentation for ACS709 and the FAQ on their website, but being a complete newbie in electronics I have a number of questions:
I understand that I probably need to add a capacitor to the FILTER pin of ACS709, but I am not sure which capacitor should I choose.
In the FAQ they provide a formula and an example table for different capacitances, which reduce bandwidth.
What is "bandwidth" in this case? The amount of measurements per second?
I only want to measure the mean current flowing at most once per second.
Which capacitor should I choose?
--- Follow up ---
I found this equation for a low-pass RC filter:
$$ f_c = \frac{1}{2\pi RC} $$
Solving for C gives:
$$ C = \frac{1}{2\pi Rf_c} $$
According to the docs the ACS709 already has a built in resistor of 1700 Ohms. Choosing the frequency = 0.5 Hz gives me:C = 0.1872 mF
Is that a correct calculation? The result seems large. In the docs all examples are in the nF range.
I want to choose mono-polar electrolytic capacitors, because the ACS709 output should have polarity in only one direction. Is that the correct choice?