Hello
100mA is way to much for any arduino (20mA max! ) You must use some type of power relay (transistor, mosfet, darlington array)
also if you want to use voltage higher than 5v you must use them
-Nano is equip with voltage regulator but it can go hot if You draw current and supply a high voltage ( when drawing 200mA from 12v there will be a 1.5W of heat to dissipate )