The cold weather has hit the northeast united states, and with that, battery failures abound in your average automobile. Of course I cannot just get by with having to replace my battery, I instead have to replace the alternator in "trouble".
In my case, I noticed about a week ago that the blower motor sounded like it was losing power because it would spin slower than normal. As time went on, the ammeter gauge (this gauge shows you the voltage that is coming out of the alternator) would drop to minimum for a minute and then go back to normal, but at this time, the lights would dim, the blower motor would slow down, all signs that the alternator was not putting out enough voltage to run everything. It's time to diagnose and replace it.
Let me start by explaining how an alternator works:
Alternators started showing up in automobiles in the 1960's as a replacement for what was called a generator. An alternator works by spinning via the accessory belt (usually a serpentine belt that drives everything off of the crankshaft) and using a rotor spinning around a stator to produce AC voltage. The rotor has brushes on it that make contact with the stator and this whole process works off of the theory of using electromagnetism to produce voltage-thank you Nikola Tesla.
Alternator output is measured in amperes ("amps" or "amp"). The more demands are made on the electrical system, the higher the amperage required will be, and this will be discussed later in the article.
"But my car uses DC voltage!"-half the people that will read this if they know that fact.
Your alternator has a part called a rectifier that converts AC voltage into DC voltage. This voltage is then governed by a voltage regulator which allows an assumed maximum of 14.8 volts to go to the battery and the rest of the main electrical system. This does not mean that everything in your car gets the full 14.8 volts, it's just the amount of voltage available for charging the battery and running the vehicle. Some components use a mere 5 volts to operate, but that is a discussion for another day.
"So how do I check my charging system?" -half of the people that are still here instead of going to watch YouTube videos featuring cats.
The best way to check the charging system is by using a multimeter to see the voltage present in the system, I start by checking the battery with the engine off and I am looking for 12.3 to 12.6 volts. Place the leads of the multimeter directly on to the terminals and see what the voltage is, making sure that you have set the multimeter to DC. Regardless of the actual number, the next thing to do is to start the vehicle, let it run for a minute (especially in a vehicle with a diesel engine) and check the voltage available at idle. This number should be between 13.6 and 14.8 volts at the battery terminals.
Too high and you have a condition known as "overcharging" and you are risking damage to the vehicle's electronics. Too low and you are not charging the battery which can lead to being stranded as well as various components not working properly.
Another way to quickly check the alternator for operation is to, while the engine is running and without touching the wires coming out of the alternator, is to take a screwdriver and touch it to the back of the alternator's case. If it sticks (due to magnetism) then the alternator is functioning, though this may be at a very basic level. (Meaning that it may still not be producing enough voltage.) For this reason, I prefer the multimeter as a diagnostic tool in this case.
Let's talk about the battery for a minute:
If the battery is failing, one of the ways to tell at home is to check the voltage with the engine off. Again, using a multimeter, check to see if the voltage is between 12.3 and 12.6 volts. If it is not, then we need to determine why that is.
Presuming that using the charging test with the engine on showed a good charge, let's look at the battery itself. Are the terminals clean? Crusty green buildup is a surefire way to not have enough voltage going into the battery because of resistance. Is the battery itself clean? For fun, place the positive lead on to the positive terminal of the battery and place the negative lead onto the battery case itself. Is there voltage present? If there is, that is the electricity "crawling" across the battery, which can kill the battery as well. In these cases, disconnect the battery and clean up the terminals and/or the case. Is the battery cracked? Replace it and be careful when handling a damaged or dirty battery, as the corrosion and the fluid inside is acid, and it can burn your skin.
Lastly, 12 volt batteries are actually 12.6 volts at rest. They have six cells within the battery (three positive, three negative) that hold 2.1 volts each. So, let's say that you take your engine off measurement and come up with 10.5 volts. You most likely have a damaged cell, and it is battery replacement time. (I have an earlier write up on how to do this properly.) Another test that can be done, usually for free at any auto parts store, is to have the battery load tested. The test involves using a specialized tool that will measure the total amperage of the battery versus what it is supposed to have according to the label on the battery. While batteries in general for automobiles are supposed to have 12.6 volts, their amperage (which actually starts the vehicle) does vary depending on application. A four cylinder engine, for example, may only need 350 cranking amps to start, while a V8 equipped truck may need twice that amount, and diesel engines on big trucks may need north of 900 plus amps to turn the engine over.
Enough talk, let's swap out the alternator!
The cause of failure in my alternator was the regulator failing. As the regulator is built into the alternator, replacing the entire alternator is going to be the course of action that I will take. Other things that need to be checked are the battery cables and cables going into the alternator. You are looking for damage, including damaged insulation, loose cables/wires, outright failure of the cables (i.e. they are broken), corrosion, etc.
The first thing you need to do is to disconnect the battery cables from their terminals, starting with the negative terminal to prevent sparks. Some say that this is all you have to do to ensure not getting shocked by the battery, but I prefer to completely disconnect the battery to completely eliminate that possibility. The cables are not always red (positive) and black (negative) so if in doubt, mark where the cables were attached.
Second, release the serpentine belt (most common in today's vehicles) by moving the tensioner. Most cars and trucks have a belt diagram that shows you which pulley this is under the hood. If not, look for a pulley on a bracket with a square in it. Usually a breaker bar or ratchet end will fit into the square. Move the bracket to take the tension off of the belt and remove it from the alternator pulley while the tension is released. Do not let the belt catch your fingers between the belt and the pulley as this will hurt. Set the belt aside and try not to disturb the rest of the belt positioning, especially if there is no belt diagram.
Third, disconnect the cables from the alternator. There are usually two sets, the cable that allows power from the battery to go into the alternator and the set that distributes said power coming out of the alternator. These will be electrically "dead" if the battery was fully disconnected, so set them aside.
Fourth, unbolt the alternator from the engine. There are usually two or three bolts that hold it on, and they generally are installed in specific locations based on bolt length and sometimes bolt head size. Make a note of where they go and, once they are removed, remove the alternator.
Before the new alternator is installed, go ahead and clean up the battery terminals if needed. This can be done with a battery terminal brush or wire brush, cleaning up with water. Do not use baking soda and water because if the baking soda gets into the battery, it can ruin it.
Install your shiny new alternator, reattach the cables going into it, and reinstall your drive belt, making sure that the belt is fully seated onto the pullies. Reconnect your battery, starting with the positive cable first (to avoid sparks and such), then the negative cable. Start the engine and check the charging voltage. There should be the aforementioned 13.6 to 14.8 volts with the engine running at the battery terminals.
If you are still here reading, then let's discuss the amperage that an alternator can produce, and since you have found yourself interested in replacing your alternator, now is a good time to consider if you require more power (in amperage) out of it. Cases to consider would be if you have a big aftermarket stereo system in your car or if you have a truck with a lot of aftermarket lighting. Maybe you are building an ambulance with all sorts of lights and sirens, not to mention the additional power needed to run the back end of it, with all the emergency medical equipment in there. If any of this is the case, then maybe your stock amperage alternator will not handle the load required to power everything.
For example:
Let's say you have one of those little pocket rocket Japanese cars with at best a 90 amp alternator, but you added on the big aftermarket stereo, a pair of fog lights, an amplifier and a pair of giant subwoofers for the sole purpose of sharing your "music" with everyone in a ten block radius. Let's also say that while you have this 90 amp alternator, the electrical demands under normal circumstances are 80 amps. You now have ten amps left to power all the aftermarket items that were not taken into consideration by the manufacturer. If the alternator cannot meet the amperage demand, then you will see the lights dimming, your music may become more distorted than usual, and this can go as far as to create drivability complaints. One way to compensate for this is to go with a higher amperage output alternator.
With say, a 140 amp alternator, you now have 50 additional amps to run all the aftermarket items. Does the voltage increase? Well, no. The regulator will still hold things at 13.6 to 14.8 volts total availability. What this does mean is that the amperage will be available to not cause power losses, especially when the stereo is on, the aftermarket lights are on, etc.
A higher output alternator may also help with starting on a cold morning by increasing the total amps available to the starter initially. It is important to note that a 90 amp (or any amperage) alternator will not necessarily produce 90 amps all the time, but if the demand is present, it will increase as needed, generally determined by sensed load demand, usually determined by the vehicle's electronic control module (ECU).
So, what causes an alternator to fail?
In most cases from my experience, the most common cause of failure is age. An alternator has a few moving parts aside from the aforementioned rotor. They generally have bearings at either end, a cooling fan, a main shaft, etc. There are also windings and diodes within the assembly. All this being said, it is usually age that does an alternator in. Of course, if a diode ends up cracking or a bearing fails, this will shorten the life of an alternator significantly.
Is it possible to drive without an alternator?
Well, not for long because of all of the electronics found in today's automobile. The farther you try to drive without a working charging system, the more likely malfunctions are going to occur. This is because of the sheer amount of voltage required to actually run the car. Once systems start falling below their required voltages those systems will stop working properly, if they work at all..
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