While there are a number of variations on the theme, all motorcycle alternators boil down to two types. The first and less common is the automotive-type, externally mounted, self-contained “one-piece” alternator, wherein everything needed to create and regulate the current output is housed in one unit. These are typically driven by gears or a small chain from the crank, which allows the manufacturer to gear it up or down as required to achieve the correct rotational speed and current output. Because they’re the most powerful type of alternator, they also create the most heat, which is why they’re mounted externally. Alternators like these are sometimes found on large touring bikes, like the Honda Gold Wing, where lots of generating capacity are required.