I plan to drive a BLDC motor using a sine wave controller and will use a 500A 75mV shunt resistor (150µΩ) to measure current in the circuit, where the maximum current will be 300A. I have some questions regarding this setup:
Are there any potential issues that might arise when operating the circuit as shown in the diagram?
The voltage generated across the shunt resistor will be very low, so I need to consider the ADC input. I am planning to amplify the signal using an OP-AMP. Is it sufficient to use just the OP-AMP, or would it be better to add an external ADC, such as the ADS1115, for more precise measurements?
Would adding a capacitor help suppress high-frequency noise? Could you advise on selecting an appropriate capacitance?
Shunt Resistor vs. Hall Sensor – Which would you recommend for more accurate current measurement?
If there are any additional considerations for achieving more accurate current measurements, I would appreciate your insights.
The regular Arduino (Uno, etc.) has an optional 1.1V ADC reference. That makes each count about 1mV so depending on how much precision you need, that may be the best solution. (You'll probably get less noise than with an op-amp).
If you are powering an op-amp from 5V, make sure to get a "rail-to-rail" op-amp so the output can go from zero to 5V. With a regular op-amp you might loose a volt or so on both ends.
P.S.
Although you're only expecting a few mV when everything is working correctly, if there are higher voltages present you might consider using an over voltage protection circuit to protect the op-amp and Arduino. For example, most multimeters are rated up to 600V or so, even on a low-voltage range.
I think 45mV is a very small value and won't have a significant impact. However, considering your point, it might be better to use a Hall sensor. Thank you.
If you decide to use the shunt current measuring system I would strongly suggest that you use a differential input amplifier to isolate your system from the motor. This should help avoid the possible ground loop problems with direct connection.
Some time ago I used IC from Zetex ZXCT1080 High voltage high-side current monitor.
Inserting the resistor in the high side of the power rail might be benefical in some cases.
After reconsidering, the shunt resistor method seems to have potential issues in terms of circuit safety and reliability. The common ground voltage difference could cause measurement errors, and additional circuit design would be required for stable measurement in high-current situations.
I considered using a differential amplifier (OP Amp) with a shunt resistor, but the OP Amp needs to have a sufficiently high voltage rating. In the end, using a Hall sensor seems to be the better option.
300 Amperes is a very dangerous amount of current, and extremely large conductors (AWG #0000) are required to avoid voltage drops, power loss and measurement errors.
Typical consumer grade instruments have accuracy 1% of full scale, so for a 500A shunt or 500A full scale Hall effect sensor, the "true" value of a measurement would be within +/- 5 Amperes of the measured value.
And then there is the problem of calibration of your measuring system. Do you have access to a separate device with current calibration in order to make corrections to your ampmeter?
