How to check the Harley-Davidson charging system

Checking the load system in 3 steps

On this occasion, we will perform an eminently practical tutorial to check if the charging system of any motorcycle works properly.

Before starting with the tests, we will briefly define the components:

The alternator

It consists of a rotor with magnets or magnetic dish, which revolves around a fixed winding called a stator. The variations in the magnetic field of the coils generate alternating current (like the one we have at home). The faster the engine turns, the more voltage we get.

The Rectifier-Regulator

The alternating current is not too useful on a bike, as it does not allow the operation of electronic devices. This is why the output of the alternator is placed in the regulator, which converts the alternating current into a continuous current, with positive and negative. This is called to rectify the current.

At the same time, the regulator controls that too much voltage does not reach the electrical components, to protect them, eliminating excess current through the chassis.

The battery

This is an element that allows energy to be stored from the regulator. In this way, when the engine is stopped or works at low revolutions we can have current to move the starter motor, the lights and other electronic components.

Another very important function of the battery is the electric "shock absorber", filtering the current that arrives from the alternator and through the regulator, so that the electronic components function with great precision and stability.

Three-step test

To perform a quick check of the charging system we only need a multi-meter capable of reading continuous and also alternating current. We shall proceed as follows:

• We put the multimeter in alternate voltage measurement (VAC), we disconnect the connector of the alternator, we start the engine and we measure the output of the same. We should obtain some 40V, which increase progressively if we accelerate (it is essential to consult the data of the workshop manual for each year and model of motorcycle, since this measurement varies greatly). If the alternator works correctly we move on to the next test.

• With the motor stopped and the contact in "off", we measure the continuous voltage (VDC) in the terminals of the battery. It should be 12V or greater. We start the engine and we remeasure. The voltage should go up to 13V or higher. With this test we have checked the condition of the battery and the operation of the rectifier. We move on to the next test.

• While measuring as in the previous step, we accelerate and check how the voltage goes up, until it stabilizes around the 14V even though we accelerate more. This indicates that the current regulator is performing its function correctly, this point we can also check with the bike's own voltmeter, if you have the same.

Checking these 3 points will take no more than 5 minutes, and we will be able to know if the charging system works properly or if there is any problem in any of the components. As always, consult the workshop manual for specific specific values for the bike you are working with.

Frank Burguera

#mecanicaharley