Alternators

To generate electricity, you need a magnetic field and an electrical conductor. Both must move relative to each other. The electrical conductor, i.e. a copper wire, is wound as coil(s) around an iron core; the iron core serves to amplify and align the magnetic field. The magnets that generate the magnetic field are built into a steel jar and allowed to rotate around the coil. If the rotation is fast enough and the magnetic field is strong enough, a voltage can be measured and current can be drawn from the wire ends of the coil. The current constantly changes its direction of flow, so the coil must be connected to a rectifier before it can be used to charge a battery. In order not to overload the battery and the other circuits, the voltage and current must be regulated. However, the alternator designed in this way is not subject to mechanical wear like the DC generator, and it can deliver much more electrical power than the latter for a comparable size.

Alternating current or three-phase current?

The difference comes from whether there is one or more coils and how they are interconnected. With alternating current, the entire current pulses in waves from a positive maximum to a negative maximum. With three-phase current, three (or six, or nine ...) coils are connected in such a way that three alternating current waves constantly superimpose on each other in such a way that the effective voltage is much higher than with normal alternating current. Three-phase alternators are therefore the first choice when the demand for electrical power is higher: electronic control units, fuel injection, on-board computers, bus and control systems ask for power. That's why three-phase charging systems have been found on Harley-Davidson's Sportster models since the introduction of HDLan in 2014 and on the Big Twins since the early 2000s, in parallel with the SAE J1850 single-wire bus.

How do you tell the two types apart at a glance?

The stators (coils) of AC alternators have two terminal connectors, while those of three-phase alternators have three terminal connectors. There is only one exception: 1970-1975 1200 Shovelheads had an AC alternator with four (!) connectors. However, the matching regulators for this have no longer been available for decades. The corresponding aftermarket regulators make use of only three of the four connection pins and are internally wired exactly like the regulators with two connection pins.

Can alternators be repaired - and what spare parts are available for them?

Alternators are simple in design, rotors (the magnetic bells) and stators (the coils) are replaceable, but model-specific. Our selection is correspondingly large, covering Sportster, FLH, FX, FXR, Touring, Dyna and Softail models. We rely on brands like Cycle Electric, Accel, Spyke and also offer high quality solutions. If ever the regulator electronics fail there are — of course — the matching types of regulators available. When replacing any regulators that do not have a ground wire, please make sure their housing has a good ground connection.