Arlo1 said:
So I just found this http://ecomodder.com/forum/showthread.php/paul-sabrinas-cheap-diy-144v-motor-controller-6404-497.html shows it here http://www.melexis.com/Hall-Effect-Sensor-ICs/Triaxis®-Hall-ICs/MLX91205-689.aspx And the data sheet says the Melexis hall current sensor is 8uS responce time so a little slow but you could do the math and predict where the current is in 8uS more time then set your fail safe to trigger there. I will look into it tonight. Looks uber easy to inmplament!
Any of those current sensors that rely on measuring the B field directly from the trace without a flux concentrator are susceptible to cross talk from other high current traces running nearby. Allegro has a product offering that is somewhat similar too the melexis part too, but they control the trace to sensor relationship which limits the maximum current that you can sense. If your currents are going to be higher than 200Amps, I would suggest rolling your own current sensor by selecting a ferrite core and cutting an airgap so that you can fit a hall sensor. See attached document. I have rolled my own in the past up to +/-2000Amps, with decent linearity. You can also purchase off the shelf sensors from LEM if you want to do it without learning about magnetics. As for the comment about 8usec response time, for simple hall base current sensors, the response times are not usually very quick, but in terms of the typical motors that you might be trying to sense the current in, it is fast enough. Only motors with really low winding inductance and resistance values(small electrical time constants) would not work with them.