How to create a reverse voltage protection with minimal voltage drop
The instructables link shows low side switching; while that can be ok, it can interfere with low side (ground) referencing.

Here is another way to do it:







simulate this circuit &ndash; Schematic created using CircuitLab

I have used back to back parts here to prevent body diode conduction. When Vin is normal, the MOSFET gates are pulled down and they conduct.

If Vin is reversed, the MOSFETs are turned off.

It is possible to do this with just M1, incidentally. The advantage of using both devices is that it is now possible to turn the circuit off completely without powering the supply off (with some small circuit additions).

The key parameters for the MOSFETS:
Vgs should be rated at 10V for low Rds(on), Vds should be 20V to get a bit of headroom.

Look for the lowest Rds(on) that is available and make sure the part can handle the power (look at the thermal characteristics).

It is not uncommon to see a large (1M or so) resistor at he junction of the source terminals to the negative side of the power for balance.