Generators and Corresponding Regulators
Direct current generators briefly explained
Do you still remember the experiment from your physics lessons? A magnetic field can be made visible with iron filings. What you see there, the physicist calls field lines. If you move an electrical conductor - a copper wire, for example - across the field lines, an electrical potential is created in the wire: one end of the wire is charged negatively, the other positively. If you connect the ends of the wire to a small light bulb, current flows and the bulb lights up. Now we only have to improve and multiply the individual parts: we replace the magnet by two electromagnets (field coils), the single wire by compact windings (armature coils) and we couple the movement of the armature coils with the crankshaft. With this construction we can operate headlights, charge batteries, feed ignitions, in short, we have a generator.
In the DC generator there is a built-in rectifier, the collector. All armature coils are connected with their two ends to one of the plates of the collector (this is the name of the ring-shaped arrangement of the plates). We draw current from the coils through the collector plates via carbon brushes whenever it is at its highest. Every few revolutions the brushes have contact to a new plate or coil. In this way, we achieve that only positive voltage is applied to one of the brushes, and only negative voltage to the other - exactly opposite.
Why do some generators have three carbon brushes and others only two?
In the first generators used by Harley-Davidson, the field coils were connected in series one after the other, with one end connected to the positive carbon brush and the other end connected to a third carbon brush at an angle of about 60° to the negative one. This circuit causes the magnetic field in the field coils to build up by itself as soon as the armature starts to rotate. The exact position of this third carbon brush is adjustable. It determines the strength of the magnetic field and thus the output of the generator.
In the 1930s, there was a small change. Only one of the two coils was connected to the third carbon brush, the other coil received the excitation current directly from the battery, but only in the light position of the ignition switch. This produced more current for the additional loads (headlights and taillights). The circuit with only one regulated coil was enough for the current consumption of the ignition.
In the generator with only two brushes, both field coils are connected in series. One end is connected to the positive carbon, the other is connected to a terminal on an external component, the regulator, via a terminal on the generator marked F (F for field). This is how you get the generator to produce more and much more consistent electrical power. And why more power? Cops ordered their Harleys with radios as optional extras - real power hogs! - and those who wanted to stay in the government business had to deliver. The world can be that simple ...
Can DC generators be interchanged?
Yes, starting with the model 32E. This generator type that was used in all 45" and 74" (and later of course 80" and 61") two-cylinder engines from 1932 on. The two mounting bolts of the generators from 1932 to 1969 (1200s) and 1984 (Sportsters) have the same bolt circle and sit exactly 180° opposite each other. The 32E (6 V) with three carbon brushes has 1/4"-24 thread, the later 58 (6 V) and 65A (12 V) mentioned - with two carbon brushes - have 5/16"-24 thread. The 5/16" can be made into a 1/4" with wire inserts, and the small threads can be drilled out or sleeves made for the screws. The rest of the on-board electrics will of course need to be adapted (regulator, battery, bulbs).
What spare parts are available for generators?
For Harleys we have complete generators from leading manufacturers like The Cyclery or Cycle Electric in 12 V or 6 V versions.
We also have many spare parts to ensure trouble-free repair of tired generators: bearing support plates, bearings, field coils, armatures, carbon brushes, pinions, gaskets and complete repair kits.
Have any questions?
Our service team will be glad to help out: Mondays - Thursdays 08:00-17:00 CET, Fridays 08:00-16:00 CET, Phone: +49 / 931 250 61 16, eMail: firstname.lastname@example.org