Quote:
Originally Posted by Al Skierkiewicz
When you push a robot, the motors begin to act like a generator. The speed controllers (both Victors and Jaguars) use power FETs that have a diode internal to the devices. As you generate current in the motors, that current forward biases the diodes in the FETs and since they are in a bridge configuration, power is back fed to the electrical system. There is no way you can generate enough current to back feed a full 12 volts to the system, but you can generate enough to light some LEDs and make it look like you have an electrical problem. All of this is normal.
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Actually, it is possible to generate more than 12V - you just have to back drive the motors faster than the 12V speed. It is hard to do this with drive motors, but possible if you have a manipulator that is heavily geared down or a bunch of students.
Another thing to consider is that when the speed controllers are being back driven through their diodes, their ability to handle current goes
way down. These diodes are usually about a volt (they are worse than intentional diodes), where as when they are turned on they are usually a couple milliohms. Consider that at 10A you are dissipating 10 W instead of .1W in those FETs, and that the fan isn't on.
I have seen components destroyed this way, but it took a lot of physical effort - several students pushing a robot geared for torque (not speed) at running speed to see what happens. They got sweaty, the electronics got unhappy.
In conclusion, it is normal but not recommended.