Alternator Altercation

By Glen Beanard technical contributor

Electricity 101 and

In a previous article about batteries, we discussed some basic electrical principles. We discussed voltage, amperage, and resistance as being like cars passing along the roadway. Voltage was referred to as the vehicles speed, amperage as the number of vehicles on the road at the same time, and resistance as potholes in the roads surface. We also defined electricity as: A supply of atoms with an

excess number of electrons. The flow of electricity would then be the actual exchange of electrons from atom to atom.

Keeping with the same analogy as before, we are going to add Diodes, DC current, AC current, and define the term short circuit.

Diodes are one-way traffic cops. They only allow the electrons to flow in one direction, similar to a one way sign on the streets; they are the check valve in an electrical circuit. The 2 ends of a diode are called and anode (+) and a cathode (-). The cathode end of the diode has an extra amount of electrons stored in its materials. The anode has a shortage of electrons. Electrically, the anode has holes that happily accept those extra electrons from the cathode side.

In the above figure, the light bulb is glowing because at the junction (green) between the anode and cathode, the holes and the electrons meet. The electrons then fill in the holes, lower the diodes resistance, and current then flows through the circuit.

In this next figure, I turned the battery around. In that illustration, the light bulb isnt lighting because the electrons and holes are being attracted to the battery posts. Since they are moving in opposite directions, the resistance is high at the junction (white) between the anode and cathode. With the high resistance the electricity wont flow, and therefore wont light the bulb.

The terms Direct Current (DC) and Alternating Current (AC) refer to the manner in which the electricity flows within the conductor.

In DC, the electrons all flow the same direction. Much the same as vehicles all traveling down a single lane of traffic, all of them moving in the same direction. AC however, will require a little more imagination to picture. The electrons dont flow so much as they vibrate.

They move in one direction, then change direction moving completely the opposite way, then back again and so on. This would be one area where my illustration of cars traveling on the road is weak when explaining electricity. After all, its not every day you see people repeatedly slamming their cars in drive, reverse, drive, reverse, and so on unless they are stuck in the mud. But you get the idea.

A short circuit resembles a driver cutting across a parking lot to avoid a traffic light. Just as that would be a wrong course of action for a driver, it is also an unwanted path of electrical flow in a circuit. The biggest problem with a short circuit is that the unwanted flow path often has little to no resistance to provide any flow regulation. The electrons will prefer the path with the lower resistance. They will overcrowd (so to speak) the wiring and melt it, possibly resulting in a fire. That is, of course, if there is no emergency kill switch in place to stop it. The fuse (sometimes a breaker or a fuse link) is that emergency kill switch. The fuse melts to stop the flow before it melts the wiring. Fuses are in place for emergency reasons. They only blow if the amperage has reached an emergency level. They do not get hot under normal conditions, therefore they do not blow under normal conditions with age like a light bulb. When they blow, they create an open circuit where no current flows at all. Compare the next 2 illustrations.

Getting a Charge Out of It

The purpose of the an alternator is to supply the power needed for all electrical items on the vehicle, plus, replenish the battery fully from the last start up. If the battery doesnt get replenished fully, it will remain in a state of discharge, it will sulfate, and it will become inactive prematurely. Keep in mind though, that the alternator is not a battery charger so much as it is a battery maintainer. An alternator that has to recharge a battery that is overly discharged can over work it shorten its life. This is largely due to the high amount of heat produced by the alternator during its charging process. The greater the amperage flowing through it, the higher the heat. So, anytime an alternator is replaced, the battery should be fully recharged with a battery charger or replaced.

An alternator transforms the mechanical energy from the belt into electrical energy. To make this energy transformation possible, the alternator actually barrows a few electrons from the battery to get the process started.