ACTIVITY 01 – TESTING OF AUTOMOTIVE ALTERNATOR Note: The procedures presented here are performed by well-experienced and trained automotive technician. DO NOT IMITATE IF YOU DON’T HAVE ANY EXPERIENCES IN AUTOMOTIVE ALTERNATOR TESTING. AIM To acquire knowledge on the procedures in determining the working conditions of alternators commonly used for automobiles. INTRODUCTION THEORY An alternator is a type of electric generator used in modern automobiles to charge the battery and to power the electrical system when its engine is running. Alternators have several advantages over direct-current generators (dynamos). Alternators are: • Lighter, cheaper, and more rugged • Can provide useful charge at idle speed • Use slip rings, having greatly extended brush life over a commutator • The brushes in an alternator carry only DC excitation current, which is a small fraction of the current carried by the brushes of a DC generator, which carry the generator's entire output A set of rectifiers (diode bridge) is required to convert AC to DC. To provide direct current with low ripple, a polyphase winding is used and the pole-pieces of the rotor are shaped (claw-pole). Automotive alternators are usually belt-driven at 5-10 times crankshaft speed, much faster than a generator. The alternator runs at various RPM (which varies the frequency) since it is driven by the engine. This is not a problem because the alternating current is rectified to direct current. Alternator regulators are also simpler than those for generators. Generator regulators require a cutout relay to isolate the output coils (the armature) from the battery at low speed; that isolation is provided by the alternator rectifier diodes. Also, most generator regulators include a current limiter; alternators are inherently current-limited. Typical passenger car and light truck alternators are rated around 50–70 A, though higher ratings are becoming more common, especially as there is more load on the vehicle's electrical system with air conditioning, electric power steering and other electrical systems. Very large alternators used on buses, heavy equipment or emergency vehicles may produce 300 A. Semi-trucks usually have alternators which output 140 A. Very large alternators may be water-cooled or oil-cooled. Photo: Cut-away of an alternator, showing the claw-pole construction; two of the wedge shaped field poles, alternating N and S, are visible in the center and the stationary armature winding is visible at the top and bottom of the opening. The belt and pulley at the right-hand end drives the alternator. PROCEDURES 1. Use a voltmeter. If you have a multimeter, you can use that instead. A multimeter measures voltage as well as other electrical properties such as current and resistance. You want to measure voltage when you're checking your alternator. 2. Check the battery first. The battery is needed to start the vehicle, which, in turn spins the alternator at sufficient speed to keep the battery charged. This means that if your battery is too low, you will be unable to start the vehicle and thus you will also be unable to test the alternator, rendering any additional voltmeter-testing totally useless. If the weather is cold or your battery is old, your battery could be the issue and your alternator might be just fine. That's why you need to check the battery before checking the alternator. Here's how to do it: • Turn off the car. You'll want to make sure your engine is off before attaching the voltmeter. • Open the hood. • Connect the voltmeter to the battery. Place the red lead of the voltmeter to the positive battery terminal and the black lead to the negative terminal. Avoid touching your skin to the battery. • Read the voltmeter. If the battery reads above 12.2 volts, it has enough juice to start the alternator, which can then be tested with the voltmeter. • If the battery doesn't have enough voltage, either get the battery charged and re test or try a different method for checking the alternator. 3. Start the vehicle and rev the engine to 2,000 RPM. This will draw power on your battery, which should cause your voltage regulator to kick the alternator into high gear. 4. Keep the engine running and retest the battery with the voltmeter. When you read the voltmeter this time, the voltage should go up to at least 13. If varying the RPMs causes the voltage to fluctuate between 13 and 14.5 volts, your alternator is in good shape; if, on the other hand, the voltage remains the same or decreases, your alternator isn’t working properly. Repeat the process with the lights, radio, and AC on. The alternator is charging if the battery voltage stays above 13 volts with the engine at 2,000 rpm and all accessories on. SUPPORTING VIDEO Link https://youtu.be/LGB6ZEjGm7Q (Read the ‘Disclaimer’) RESPONSE For your answers, see the link provided in this post.
