Here is a little exploration/introduction of the subject of motorcycle, ATV, and other powersports charging systems, as observed by a career powersports technician.
Powersports Charging Systems Are Unique
Traditionally, powersports manufacturers have built charging systems much differently than have car manufacturers. Two reasons. First, most powersports vehicles have no place to stick a conventional automotive-style alternator. The manufacturer therefore makes the rotating, generating basis of the system -- the generator if you will -- *part of* the engine, that is, blending it into it, instead of making it simply a bolted-on attachment as on cars. The result is that the supporting charging system parts (rectifier, regulator, etc.) are spread out all over the powersports vehicle. I like to refer to this typically powersports charging system picture as a "modular" configuration. On cars of course the alternator is a unitized package, with all the charging system parts contained within that package. I call this the "integral" system. Very few powersports vehicles have ever used this automotive-like integral alternator charging system. So, physically, things are quite different, even if there are are some similarities, between cars and motorcycles.
The second reason powersports charging systems are so different from cars' is that powersports vehicles have been made in a wide diversity of styles. Powersports itself is an industry producing and supporting very diverse products. With scooters, mopeds, personal watercraft, snowmobiles, utility vehicles, ATVs, recreational utility vehicles, and motorcycles in the mix, no one style of charging system will do. A moped needs a different system than does a motorcycle, an ATV a different one than a personal watercraft. This is true not just due to differing power requirements with widely varying vehicle sizes, but more importantly, also to the construction, location, drive method, cooling method, water or oil tightness and other considerations that vary with each vehicle type. This is nothing like the automotive world where one basic design is used (though different sizes), driven by a v-belt, and fully contained with all is supporting electronics inside the integral alternator housing itself.
The powersports charging system's modular construction brings its own problems of parts identification (they differ tremendously in appearance) and individual parts troubleshooting. In addition, having all these parts scattered around the vehicle multiplies the number of possible failure points in wires and connectors. Even when not failing, resistance adds up in the multiplicity of connections, which even while within design parameters, is not such a good thing. The common powerwports engine-based generating unit also is affected by the engine's heat, and even more significantly, its operating speed is strictly fixed to that of the engine's crankshaft, limiting the freedom manufacturers might otherwise have determining output characteristics. (This last point is the not often realized source of the angst of those who regard vintage motorcycle charging systems as archaicly underpowered). For these and other reasons, powersports charging systems are unqiue in many ways, one of which ks that they require many times the amount of maintenance as their automotive counterparts.
Two Major Types of Charging Systems
Charging systems, no matter the vehicle, all have three things in common. They each have a coil of wire, a magnet, and one or the other of these (i.e. either the wire or the magnet) is moved to generate electricity. With things being this simple, it's no surprise that there is one fundamental split in charging system design -- permanent vs. electromagnet types. This is foundational. Permanent magnet systems have alnico or rare earth magnets, electromagnet systems have wire-wrapped pieces of steel that are only temporarily magnetized. There are also vitally corresponding differences in regulation. Although powersports charging systems in the 1940s and 1950s on larger bikes were merely smaller versions of what cars had back then -- armature-based DC generators, an electromagnet design -- the powersports world has traditionally used mostly the permanent magnet charging system. It is the most logical when so many different kinds and sizes of vehicles are at play. Economical, compact, ideal.
The two types, permanent magnet and electromagnet, have very different characteristics. Permanent magnet charging systems build output right off idle and peak fairly early in the engine's rpm range. Electromagnet systems take a while to spool up, but reach comparitively higher maximum output levels than do permanent magnet systems. The two systems are also quite different in their regulation methods. Regulation, that is, charge control, is tied directly to magnet type, so this should not be a surprise. If magnet type is the prime distinguisher, regulation is next in importance. Permanent magnet charging systems control their outlut by simply shorting it, oddly enough, while electromagnet systems control output by weakening their magnets. These are completely different approaches requiring completely different types of regulators.
To sum up, modular and integral systems are both found in powersports. All permanent magnet systems are modular, meaning their parts are distributed all around the vehicle. This is the traditional and prevailing system wherein the power generating part is blended into the engine for compactness, and then all its supporting parts bolted to the frame. An integral system on the other hand is one in which the power producing part and its supporting electronics are all together in one housing in classis automotive style. Honda's six cylinder Goldwing, some Kawasakis and Suzukis of the 1990s, and a handful of European bikes have charging systems in the integral format. It's never been common in powersports however. Permanent magnet and electromagnet systems operate very differently, output significantly differently, and are regulated in very different ways (which affects how they are to be tested).
Permanent and Electromagnet Competition
The electromagnet system, in the form of the DC generator, ruled in the earliest days of both cars and motorcycles, before phasing out in the early 60s. During the early to mid 1970s, after a decade of the permanent magnet system's dominance, the electromagnet design in AC form and suddenly surged in prominance. The reason was the permanent magnet systems had a flaw that made them unsuitable for the larger machines that were emerging at the close of the 1960s. Early examples of this crude permanent magnet system were found on the 1960s zener diode equipped Brit bikes. Their zeners actually shorted the vehicle's battery to limit charge, so contol was on the DC side, and more importantly, the zener was atrociously overloaded in this role and thus very shortlived. The Japanese came along and adapted this system for their emerging bikes, vastly improving it by downgrading the zener's role to mere voltage sensing, and adopting an SCR -- kind of a slow but heavy duty transistor -- to do the shorting function, and that on the AC side, at the stator, instead of the Brit system's DC method. The SCR based system, through reduced loading, promised longer part life. However, it was nearly as crude as the old Brit system in one respect. It really just turned charging on and off. It was so abrupt in fact that waves of electical shock were sent up and down these bikes' electrical systems. This was not a problem when nothing electronically fancy was aboard. Remember this was long before sensitive fuel injection sensors and exhaust power valves and LCD instrumentation, and computers of all kinds, on motorcycles. However, permanet magnet charging systems were doomed when larger bikes became popular and thus were largely displaced by electromagnet systems, because the permanent magnet systems were not developed well enough yet, not smooth enough in regulation yet, to be used in the larger bikes that were appearing, whereas the electromagnet systems regulated much more smoothly. In time however, the permanent magnet charging system would return to prominance.
Electromagnet charging systems have drawbacks too, but their short run (1970s to mid 1980s) was not due to this, but rather to advances in permanent magnet regulator design. In the mid 1980s the SCRs in permanent magnet systems gave way to smoother acting transistors, making permanent magnet systems suddenly comparable to the smoothly regulating electromagnet ones, and with their simpler, less costly manufacture, permanent magnet became king once again. Further development of the permanent magnet regulator in the early 2000s to field effect transistors (FET, more durable and gentler acting transistors) further established permanent magnet's sovereignty. Transistorized permanent magnet system regulation was a huge boon, a watershed development, because as mentioned manufacturers could now go back to the lighter, more compact, and more economical to manufacture permanent magnet charging system, which almost all of them did by the mid 1980s. Thus since about 1985 electromagnet systems are out of favor with manufacturers and are again in the minority on powersports vehicles. (A few late and even brand new bikes can still be found with electromagnet charging systems, but they are rare. A resurgence seems again iminent however, as integral electromagnet systems have a long history in cars and since they are belt-driven their main weakness of not charging at idle is easily overcome by simple pulley ratio, as it is in cars.) Moreover, a development as recent as 2010 has brought permanent magnet charging systems a step further yet, the emergence of the zero-cross regulator. The zero cross regulator's transistor shorts the AC wave only on the wave's downward pulse, that is, at or near the zero point in the sine wave, making the on/off transition as smooth as possible. This new zero cross system is basically a computerized FET and the best the permanent magnet charging design has to offer. A really well behaving permanent magnet charging system.
The New Challenge
Vintage bike owners are experiencing an interesting dilemma today. The appreciable growth of the heated clothing industry has produced some very high-powered options for extending riding deeper into the winter months. Unfortunately, these products, designed in the context of modern motorcycles which output three to five times as much electrical power as their vintage counterparts, clash seriously with vintage charging output levels. Consequently, some enterprising individuals have stepped up and suggested retrofits of more modetn charging system parts onto their vintage machines, and where done with good engineering and knownow this looks promising for this segment of the vintage riding public.