MartOn:
For a 50A sensor this means the accuracy of the sensor is +-0.5A on 50A. and +-0.1A at 10A, is this correct?
Arduino will have a 10bit resolution, so 0-50A will get a resolution of 0.049A. Is this correct?
Scanning sensor options and trying to get some realistic expectations is probably a good start on a project like yours.
Accuracy for the hall sensor you linked to above is with reference to full scale, so +/-1% error for the 100A sensor is +/-1A. This is also just part of the picture as there is offset error, non linearity and temperature related errors adding to this.
Sensor output is ratio-metric to 5V for 1.25 times the rated current. A 100A sensor will cover a range of 1.25x200A (+/- 1.25*100) and for 10-bit ADC, resolution is then 0.24A. Account for ADC errors of +/- 2LSB and you’re adding +/-0.96A to the above sensor error.
I use a current shunt connected inline with house battery ground. The shunt drops +-50mV for a full scale of +/-100A. To read this, I use a delta sigma 24-bit ADC and after calibration (range and offset) this gives me a resolution of approximately 50mA across the full +/-100A range.