The Charging System Part 2: The Alternator

   As we have discussed before, the battery is the heart of your electrical system. But you need something to keep the battery charged or it will lose its charge and die. This is the job of the alternator. The alternator produces electricity and delivers this electricity to the battery and maintains a full charge at all times. If the voltage produced by the alternator goes above 13.5 - 14.5 volts, the battery will be ruined very quickly. It's the job of the voltage regulator to keep the output voltage between the 13.5 - 14.5 volt range.

   An alternator is the device used to produce the electricity the car needs to run and to keep the battery charged. The alternator uses the principle of electromagnetic induction to produce voltage and current. The four main parts of the alternator are the Rotor, Stator, Diode Pack, Voltage Regulator and an Ammeter or Indicator Light to inform the driver of any problems. All of these parts must be in good working order for the alternator to do its job. Let's take a look at each of these parts and what they do.

   The rotor is basically a magnet that rotates inside thousands of loops of copper wire wound around a core of iron. This wire wrapped iron core is the stator. As the rotor spins inside the stator the magnetic lines of force cut through the copper wire inducing a voltage. This is the voltage that will go to the battery.

   The only problem is this produces AC current and your car runs on DC current. So we need something that will convert the AC current to DC current. This is the job of the diode pack. A diode is an electrical one-way check valve that will let current flow in only one direction. The typical diode pack uses four diodes to accomplish this. AC current is feed in on one side of the diode pack and DC current comes out the other side. The diode pack also works the dash ammeter or indicator light.

   Okay, now that we have a DC current that the car can use, we need a way to control that current. That is the job of the voltage regulator. As the name implies, it regulates the voltage going to the battery. It does this by turning current to the field (stator) terminal of the alternator on and off. If the battery voltage goes below 13.5 volts, the voltage regulator sends current to the field terminal and allows the alternator to start charging. Current will then flow into the battery and bring it up to full charge. If the voltage goes above 14.5 volts, the voltage regulator shuts off the current to the field terminal and keeps the battery from overcharging and cooking itself. This is how the voltage regulator controls the alternator output.

   When you first start your car, the alternator needs some current to start working. The voltage regulator supplies this current to the field (stator) terminal of the alternator to get it started.