Curiosity. Knowledge. Power.: Alternators

Alternators

An alternator is a very important part of an engine. It is a mechanical component that uses the energy from the engine itself via a belt and pulley, to charge the battery. It uses magnetic forces and electricity to supply power to the battery (and headlights).

Since the alternator uses magnetic forces, it would generally give an alternating current. If I were to draw a graph showing the current flow of an alternator, it would be very wavy. The alternator has a built in device called a regulator, it's job is to basically convert the alternating current into a direct current (D/C). It has diodes built inside to allow the flow to only go up, as the magnet moves toward the magnet. as the magnet moves away, it creates a wave that moves downward. This current is cancelled out by the diode.

Since the alternator is connected to the engine via pulley and belt, It spins faster as the engine spins faster. This creates voltage levels that can go very high, high enough to damage the battery. It is also the regulator's job to keep the voltage output level to around 12.8V to 14V. Hans explained that a claw like design that adjusts the magnetic force between the magnets in the stator. This lowers the voltage output level overall.

The design of the alternator is quite simple.

[diagram]

Wednesday was when we dismantled an alternator (it was quite a mission, it involved hammers and clamps, and quite a beating) Hans showed us common failures in alternators, which include worn out brushes, worn bearings, un-adjusted belt tightness and awkward positioned pulleys. I read this great article on alternators. I think it is very well written. It describes what and how alternators are and their job in a car, to an extent that it is understandable but not to technical. I usually prefer full on technical but sometimes it can be hard to understand. http://misterfixit.com/alterntr.htm At the bottom of the article, it asks very basic questions you would need to know when inspecting a failing alternator. I was happy to know what it meant, when it mentioned 'voltage drops'.

How does it work?

I have quite a rough understanding on how alternators work, but I think it will be enough to pass a test.

An alternator first of all, is called an 'alternator' because it produces an alternating current. It works by a rotating component, called a rotor, which has magnets built around it. As this rotor rotates inside the stator, the magnets are forced to move through a stator, which is basically another component that surrounds the rotor, which is built up of four sets of coil, which are wrapped all around the rotor. This magnetic field produces an alternating electrical current. At the very tip of the rotor, is a small end that is connected to the rotor magnets, this also rotates but contacts a part of the regulator called the 'brushes'. The brushes are tensioned onto the rotor tip by springs. Since there is friction on the brushes, they generally wear out and begin to lose contact with the rotor. The rotor relies on the bearings to rotate smoothly. The bearings are very high quality needle bearings, so they are quite sensitive. Needle bearings have smaller parts than ball bearings, there for any dirt or residue can affect the bearing performance even more. The regulator is another component in the alternator, which since the alternator produces an 'alternating current' (A/C), it converts it into direct current (D/C), by the use of diodes. The alternator is connected to the car battery via one large cable that runs straight to the battery, and the housing bolted to the engine acts as the negative, or grounding. On the exterior of the alternator, is a pulley, connected to the rotor inside, which is connected to the engine itself via a belt. This belt needs to be fairly tight, but not tight enough to put stress on the bearings.

Common tests to check alternators condition, or procedures to take when car is showing symptoms of alternator failure include:

1. Perform load test on the alternator. Check voltage output when load is put on alternator. (lights and electrical gadgets turned on while engine is running).

2. Check belt tension. Belt must be fairly tight, but not so tight that it puts stress on the alternator bearings (bearings will make a sound when under too much stress). Check that the alternator belt is not making any squeaking sound.

3. Measure voltage availability and voltage drops. Also measure resistance anywhere around the circuit.

Some main parts: