All You Ever Wanted To Know About Alternators

The alternator in your car is part of its central core of electrical components and is essential to the operation of your vehicle. It is the device that converts engine power to electricity for use in the various electrical systems of your car, including spark for ignition, your audio system, and the headlights, among many others. On its face, an alternator is a fairly simple device, but it's far more complex than many might believe.

Modernizing Cars with Alternators

In the 1960s, the simple generators under the hood of most cars began to be replaced by more sophisticated alternators, which paved the way towards more complex electronics throughout the vehicle's makeup. They first appeared in the 1960 Chrysler Valiant, though a type of alternator with simpler electronics was fitted to the early Ford Model T for a few years ? the electrical system on those vehicles was used only to power the trembler coil for spark. When electric lighting was added to the Model T, this alternator was too underpowered and was replaced with a standard dynamo that was used on every other car of the period.

Alternator Process

The alternator itself gets its name from its power production, which is alternating current (AC) that is then converted to direct current (DC) through a diode bridge of rectifiers. Alternators have several advantages over direct-current generators, not the least of which is that they are lighter, cheaper, and more rugged due to the higher power output they can provide from a smaller package. Brushes last longer than in DC generators, since they only carry the excitation current.

Most alternators are mounted to the engine as an accessory off of the serpentine (accessory) belt. This belt turns the pulley at a ratio from the crankshaft pulley of about 2-3:1. Since the AC is rectified to DC, the variance in production from varied RPM rates does not matter.

The alternator works using a Lundell field construction. This is often referred to as 'claw pole' and is comprised of a shaped iron core on the rotor with a single coil winding. Each pole is configured in a shape that looks like two hands with interlocking fingers, which shapes the magnetic field generated. The coil fits within the field and slip rings and carbon brushes supply current as it rotates. Alternators in cars are usually air cooled by a fan attached to the pulley from the drive belt.

Evolving Designs

Improvements over time have allowed alternators to become smaller and more compact. Because a power generator of this general type is just an electric motor in reverse, most hybrids like the Prius use their motors as alternators during braking to provide power back to the batteries in regenerative braking. Hybrid Synergy Drive, in fact, often uses one of its two motors as an alternator to power the other during normal operations.

All in all, alternators have to major functions still:

  • Charge the battery while the car is running
  • Keep the draw of voltage from draining the battery