Your car's alternator has two important jobs. It Keeps the electrical system running and also recharges the battery. If your alternator stops working it will no longer charge the battery. This results in it draining and preventing the car from starting. While alternators can suddenly fail, there are often tell-tale signs that it is on the way out:
-
Sometimes it may produce a squealing noise.
-
At night, you may notice that your headlights are pulsing with brightness.
-
You may also get a battery warning light on your instrument display to signify that it is not recharging.
These signs may give you some warning before the alternator fails. Which could potentially end up leaving you stranded by the side of the road.
How does an alternator work?
It works with the battery to provide power for the electrical system in your vehicle. It is usually found near the front of the engine. A belt connecting the crankshaft pully and alternator provides it power. Inside the alternator are a rotor and a stator. The rotor is an electromagnet that spins inside the stator, which consists of a set of wire coil windings. As this rotates, it generates electricity that's fed into the battery via a regulator. The regulator ensures a steady rate of voltage.
What causes an alternator to fail?
The usual cause of failure is the breakdown of the needle bearings that allow the rotor to spin. This happens as a result of dirt and heat over time. This process can sometimes take many years of build-up and heat cycles to occur. In modern cars alternators can last for many years. But, there is no set time for how long they can last. Having a failing battery can also reduce the lifespan of an
alternator. It can place an increased load on it as it tries to recharge the battery. This combined with having to power other systems in the car, makes life much harder for your alternator.
Is it the battery or the alternator?
If your engine won’t start, the first course of action is the try to jump start it. If you jump start the engine and it continues to run then it's most likely the battery that is at fault. We recommend to replace it. Sometimes the battery’s capacity can come back up after a long drive, but this is not a guarantee. If its charge drops below a certain level, it is unlikely to get back up to a stable rate. What if you jump start the car and the engine dies? it is most likely the alternator that is the problem, as it is not charging the battery. 
How To Test an Alternator
It is quite simple to check to see if it's working, once you have a multi meter. With the engine running, touch the positive probe on the multi meter to the positive terminal on the alternator. Then touch the negative probe on the car’s frame or a bolt head. It should show a reading on your multi meter of around 14 volts.
If the reading is higher (15 volts or greater), then it is faulty and may soon fail. If the reading is below 13 volts, it may be a case that the engine’s idle speed is too low for it to charge the battery . Increase the engine speed by revving it to see if this solves the issue. If not, you may have a slipping bet or a regulator that needs replacing.
Replacing an alternator
The alternator is usually found close to the front of the engine. If you decide to replace it yourself, the first thing to do is to disconnect the battery to remove any risk of shock. They are often hidden behind other parts in the engine bay and can be hard to access. Once you have all the other bits and pieces removed, taking the alternator out is usually pretty simple as they're only held in with a couple of bolts. If you want to do a belt-and-braces job you might want to replace the battery and alternator at the same time.
