[Al Skierkiewicz]

Fox,
Unfortunately the answer is NO, there is nothing in the way of backward protection. The FETs have a diode that is across the terminals that results from the manufacturing process. If you look at the spec sheet you can see the diode and the direction in which it conducts. The four legs of the "H" bridge do conduct as a full wave bridge and provide power of the correct polarity at a reduced voltage backwards to the power rails of the controller. These diodes do have a forward voltage drop though, so the conducted voltage isn't quite what you would think. Remember that when the controllers are powered correctly, and a 'coast' condition is commanded, all of the FETs are off and current only flows through the diodes (the same is true for pushing with power off). When a 'brake' is commanded both low side legs of the controller are turned 'on' resulting in a short across the motor but no power being delivered to the controller internals and no current flowing through the diodes. In the case of the power leads being attached to the output terminals, we don't know if they were wired in a normal polarity. In any case, considerable current may flow through the controller restricted only by the breaker feeding the device. Depending on the duration (or repeated attempts to determine the cause) significant damage to the device might be the result. Magic smoke is almost always the result.