[Gdeaver]

As mentioned the problem with a diode is the voltage drop and heat generated with it. The current handled by the diode would have to be much greater than 40 amps. In fact it would have to handle a direct short. Many automotive motor drivers use a Fet to provide reverse battery protection. This can be done several Ways.The advantage of a power FET is the low on resistance and less power loss. A PNP Power FET could be used on the high side with the gate tied to ground with a resistor and diode. The problem with a PNP power FET is that they are not available with large current handling and low on resistance. If PNP FETS could be made with the same robust characteristics as NPN FETS they would be used in the motor drive h bridge. Multiple PNP's could be used but, that takes space and adds cost. A NPN FET can be placed on the low side with the gate tied to the V+ with the resistor and diode. The problem with low side protection is that it messes with the ground. Electronics do not like it when the ground has transience on it. A NPN power FET can be used on the high side. The problem is that the gate drive voltage has to be above V+. This requires a voltage boosting circuit adding cost and board space. ST micro makes a bridge driver chip with this circuit on the chip. The other way the jag could be some what protected from reverse polarity and swapping the V+ and motor leads would be to use polarized connectors with a different type for the V+ and Motor. Then the risk of zapping a jag would be limited to when the cables are made up. The PD would also have to have polarized connections. As long as the power connections remain as they are now, every year there will be x number of fried controllers every year. Our team has fried a few.