Alternators for Big Twins 1970→ and Sportsters 1984→

The alternator

The alternator on the Harley is not a completely separate component, as it is on the car. The stator - the coil or winding in which the current is generated - is bolted directly to the crankcase. The rotor - also known as the "pole wheel" in German - mounts on the left end of the crankshaft. With one exception: in 1986-1990 Harley-Davidson experimented with the clutch basket as a rotor on Sportster models, evidently not an ideal configuration. The regulator, which is always necessary, can theoretically be placed anywhere on the motorcycle. It makes sense, of course, to place it in front of the engine so that it can dissipate its heat while riding.

For windings as well as for regulators, we prefer to rely on the products of Cycle Electric, Inc. from Ohio for quality reasons.

How can I test the AC alternator if the battery is not charging (properly)?

The test is simple and logical and involves several steps. You need a standard multimeter to do it. Since the engine must be running for part of the measurements, the battery should be well charged.

First, access the battery and measure the voltage between the two poles. For starting without problems, the voltage (so-called open circuit voltage) should be at least 12.7 V. After starting, the voltage must rise above 13 V at idle, and when turning the throttle, the voltage must continue to rise. The maximum is 14.4 - 14.6 V. If the voltage measured at the poles during operation is above the described range, either the battery is ripe for replacement or the regulator.

If the voltage at (engine) idle is in the range of the open-circuit voltage and it increases little or not at all when accelerating, the first suspicion is always on the regulator. For further measurements, the engine must be off. In the case of a regulator without a ground cable, the resistance from the housing to the vehicle ground must be measured. For a regulator with a ground cable, the resistance at the ground point. It must be 0 - 0.5 Ω. A higher resistance can hinder the functioning of the regulator and must be eliminated.

To measure the stator, disconnect the connector from the stator to the regulator. Attention: never disconnect this connector while the motor is running! From each of the exposed terminals of the coils, the resistance to vehicle ground must be infinite. A measurable resistance from any of the terminals to vehicle ground suggests a ground fault. The stator must then be removed and tested separately.