Main breaker tripping, dead CIM

[brycen66]

Originally Posted by Ether

The op amp doesn't measure the voltage drop. It just amplifies it to a level suitable to be digitized by the A/D.

Instead of measuring the voltage drop across the main breaker, you could measure the voltage drop across a length of wire.

Although your method does make mathematical sense, it will run into an error if you use this on the 120 amp breaker. You forgot to account for the fact that even the best op amps cannot read more than 95% of the reference voltage. This means that even if you used a differential resistor setup, which I assumed from your drawing, you could not use the 5 volt supply from the analog breakout. You would need somewhere around 16 volts, which means this would have to have an independent power supply. You could get around this by using a differential op amp setup on a length of wire attached to your main ground wire, but that adds unnecessary resistance.

A completly diffrent solution would be to use a linear hall sensor such as this part (http://www.jameco.com/webapp/wcs/sto...01_1915940_-1).

Place a steel washer or ring(any ferrous metal works) around one of your main wires. Then cut a slot in this steel washer and place the hall sensor in the slot. We epoxied ours in to keep it intact. The hall sensor outputs voltage which is directly related to the total robot current, and it can be plugged directly into the analog breakout. This is the system we have implemented into our practice robot and the results so far look good.

If you have any questions feel free to PM me.