Banebots RS-775 Case Short

[EricVanWyk]

Originally Posted by Ether

I don't see how a motor case short can cause an increase in current in the cRIO negative power lead if the cRIO chassis is electrically isolated from the robot frame.

This isn't the appropriate thread for this, and I'd appreciate if this side bar could be split off.

In a double fault scenario, additional current can flow from the motor, through the chassis, into the cRIO frame, through the cRIO's fuse, out the connector, through the return wire, into the PD, through the PD's self-resetting fuse, to the negative return of the battery.

The question is a matter of timing: Which protection cuts out first? The four in play here are the cRIO fuse, the cRIO power supply undervoltage lock out (UVLO), the PD's self resetting fuse (PTC), and the return wire experiencing a rapid gaseous state transition.

My claim is that the PTC is doing what I designed that circuitry to do, and that it is cutting out first. It heals when the fault clears, and then the cRIO begins to reboot, as my fellow NI engineers designed it to.