A friend contacted us today with a question about his six year old vehicle that has been eating an alternator a year for the past three years. In the times with more complexity being built into automotive electrical systems your car’s alternator is one of the few things that should either work or not work. They normally have a life expectancy of at least 10 years or maybe much more and they are actually very simple pieces of equipment.
Your alternator is very similar to any electric motor. Internally it has outside windings around the housing and in the center there is a armature that has additional copper windings. As the shaft spins when the engine is running and the alternator belt is turning the pulley on the alternator the spinning creates Alternating Current. AC current is what is used in homes. DC current is what is used in battery systems. To convert the AC current to DC current a Diode Trio is used. The output is through a thick cable that is attached to the Positive side of your battery and the alternator gets its ground through its housing because it is physically mounted to the engine and this completes the circuit.
Its pretty easy, the engine spins the alternator and it outputs voltage that charges your battery. Anytime the engine is running and spinning the alternator it should be charging the battery.
The output will vary but it should be DC Voltage between 13.5 and 15volts measured on a volt meter / multimeter. This will allow for enough voltage to run all of your accessories and recharge the battery while you are driving and when you turn your vehicle off the battery should be charge to 100 percent.
So the problem our friend is having may be that the alternators that were installed have actually failed but it is pretty uncommon for an alternator to fail three times in three years. There is most likely a misdiagnosis or another problem causing the alternator to fail.
One way to test if the alternator is working is to run the engine and take a voltage reading directly off the positive output on the back of the alternator. This can be difficult on some cars because alternators can be mounted in hard to get to locations. You may need to jack up the vehicle and attach a lead wire with an alligator clip.
If the voltage tests good when directly connected to the alternator then you know you have another problem if it does not test good then you should make sure that you have a good ground. Oil seeping into the area could cause a ground problem as may other things. If the alternator tests good then you know it is good. If the alternator tests bad then you should remove it from the vehicle and bring it to a parts store that has the ability to bench test the alternator. If it still tests bad then you need to replace it.
If you need to replace the alternator you should ask that the alternator be inspected and that you be given a reason for it failing. It could be as we said that engine oil saturated it. It could be internal corrosion that caused a short in the windings, it could be the diode trio or a broken connector or a variety of other things but it should be easily diagnosed if the technician is knowledgeable about testing alternators.
Once you know the reason the alternator failed you will understand if it is something that you can prevent in the future or if it is a manufacturing defect that you can’t prevent.
Some vehicles that have had modified exhaust systems or that have turbos that overheat the alternator will report short lifetimes for alternators. There can be many reasons such as running your vehicle in harsh conditions but you should be able to track down why the alternator is dying and if you can fix the problem or if it is just a cause of vehicle use.
What Could Be Wrong If My Alternator Tests Good?
If the alternator tests good either on the vehicle or on a bench test at your local electric supply / parts store then you have a few more steps to follow to diagnose the full problem with your vehicle.
First start with how the alternator is mounted and make sure it has a good ground. Also make sure that all of the engine ground straps are in tact and grounding to your vehicle’s frame. There have been many instances of a single missing ground strap causing major problems including frying Alternators.
Next you want to check the cable from your alternator to your battery. An Ohm Measurement with a Multimeter can give you quick diagnosis of a really bad wire but often you can get misreadings because the wire will fail under use. If you see battery oxide on the end of the cable you might just want to replace it to be sure it is not a problem.
Most new alternators are internally regulated for voltage output and this should have been accounted for in bench testing but if you have an external voltage regulator you need to test it and replace it if it is bad. Test the voltage going in and the voltage coming out and this should be a good initial indicator of its condition.
A bad battery could also be the problem and you should have it electronically analyzed. There are a few ways to test a battery and one is a load test the other sends current through the battery. Any battery that is an issue at this point should be suspect if the alternator is outputting steady current in its specified range.
There are other parts of your electrical system that could cause issue and result in dead batteries or systems that do not operate correctly.
If you have an add on sound system, light bars or any non stock features they should be inspected.
Finally one of the most overlooked things that can cause alternator problems is a slipping belt. Belts may slip and not cause that telltale squealing noise. Inspecting the belt and how tight it is will be your first step but because they do not cost that much it would be a good idea to replace it any time you replace the alternator or run into a problem such as this.
Final Note
When you break down your car’s systems into smaller sub systems it is easier to diagnose problems however there are always things that are missed even by the best technicians.
In this case an every year for three years an alternator had to be replaced on this vehicle. Considering the normal life of an Alternator this is completely unacceptable and if the garage that is doing the work isn’t covering the cost at least for the third attempt in total then it is really in your benefit to find someone else to diagnose the problem.
Dealers are not a place that people love to go but when things are hard to fix they are often the best at diagnosing or researching problems because they have specific feedback across the whole manufacture dealer network from which to pull information.
Online forms for specific manufacturers and vehicles are also a place that you should ask questions. Do not expect official or even correct information all of the time but sometimes you will find someone that has gone through the exact thing you are going through and they can be very helpful. Most of these forms are also friendly so don’t be afraid to ask questions if you have them.