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The Electrical System:
The Alternator: The Charging System
 We’ve seen how the battery powers the starter, but without some means to recharge your battery, it is likely that after a few hundred starts, your battery would be dead. To compensate, your automobile needs a way to recharge the battery as well as power all of the electric devices, like the radio or lights while you’re driving. That’s where an alternator comes in.
The alternator functions like an electrical generator by converting the mechanical power of the rotating crankshaft into electricity. A belt and pulley assembly connect the alternator to the crankshaft. As the crankshaft turns, the alternator belt causes the alternator’s rotor shaft to spin.
Basic Rotor Construction
Coiled around the rotor shaft is a long segment of copper wire. Two claw shaped pieces of metal are mounted over the coil and face one another, similar to interlocking fingers. The opposing claws are charged with opposing electrical polarities. One claw has a north orientation and the other claw has a south polarity.
Rotor Operation
If we connect an electrical current to the rotor, we have the basics for an electromagnet. The alternator works by a process of electromagnetic induction. What that means is that the alternator is able to convert mechanical energy into electrical energy by spinning a magnetic field around a coil of wire. As the engine spins the rotor shaft, the rotor’s magnetic field passes the stator winding’s (wire coil) north then south poles. This induces a voltage in the stator windings that change from positive to negative. The alternating polarity produces an alternating current.
Role of the Brushes
Metal slip rings are connected at each end of the coil of wire. As the coil spins, so do the rings. Alternator brushes slide along the rings, creating a constant electrical connection. The brushes conduct an electrical current from the battery to the rings and copper winding.
All of the electricity produced by the alternator is alternating current (AC) but the battery, devices and electrical circuit require direct current (DC). As a result, it is necessary to convert or “rectify” the alternating current into direct current.
Current Rectification
The rectifier converts alternating current into direct current. A simple semi conductor device called a Diode acts like a one way valve that only allows current to pass it in one direction, we call this rectification.
While the operation of the alternator produces electricity, it has no way to control the amount of current generated. The amount of electricity will increase relative to the speed that the rotor (and engine) is rotating. Too much current could damage the electrical system and cause shorts or prematurely burn out bulbs or create other malfunctions. As a result, a voltage regulator was created as a means to regulate the amount (voltage) of electricity produced.
The Regulator
The regulator works by controlling the amount of electricity that flows through the alternator. The regulator constantly measures the voltage at the output of the alternator and then varies the voltage to the rotor to vary the magnetic field the rotor produces.
A simple example can explain how this works. If you’re driving 55 mph along a hilly road, you have to constantly monitor engine speed by looking at the speedometer. When you’re driving up a long hill, the automobile has a tendency to slow down, so you increase pressure on the gas pedal to keep your speed constant. Likewise, when you’re driving down a steep hill, you let up on the pedal and might even put on the brakes. Just as you might keep an eye on the speedometer, the voltage regulator controls the alternator output.
An increasing number of recently manufactured automobiles turn the job of regulating voltage over to the engine control module. However, there remain a large number of vehicles equipped with traditional voltage regulators. |
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Article Pages
1. Electrical System
2. The Battery
3. The Starter
5. The Voltage Regulator
6. Lighting
7. Lighting System Basics
8. Interior Lights
9. Voltage
10. Turn Signals and Hazard Lights
11. The Horn
12. Windshield Wipers
13. The Defroster
14. Electrical Symbols
15. Types Of Electrical Circuits
16. Electrical Circuit Defects
17. Introduction To Automotive Batteries
18. Battery Construction
19. Battery Operation
20. Specific Gravity
21. Voltage And Capacity
22. Battery Ratings
23. Testing Automotive Batteries
24. Preventive Maintenance Of Batteries
25. Optical Battery & Antifreeze Tester
26. Measuring Specific Gravity With The Optical Battery Tester
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