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Alternator keeps failing to charge the battery

edited November -1 in Repair and Maintenance
I had a new alternator placed in my 2001 Mazda MPV about 2 months ago. A month later the alternator failed and I had it replaced again, it was still showing signs of failing and I was told by the mechanic that it was the PCM. I took it to the dealer and was told it was not the PCM just the alternator. So the alternator was replaced again, different manufacturer this time. Now here I am a month later and the alternator is failing again. The dealer checked the PCM and wires and everything seems to be working fine except the alternator. They don't seem too enthusiastic about looking beyond the alternator issue.

I think the problem is deeper than the alternator, what is the chance that 3 brand new alternators don't work properly? I can get the alternator replaced under warranty but then I need to find out the real issue. Any help would be appreciated.
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Comments

  • edited July 2009
    How old is the battery, and what is its condition?
  • edited July 2009
    Like mc, I suspect you may have a battery problem, which can mimic or cause a charging problem. How old is that battery? Was it subjected to going flat due to failed alternator(s)?

    As for the chance of three failed alternators, it is better than you think. Inexpensive "rebuilt" or "reconditioned" alternators often fail. The re-builders or parts store will generally replace it with another for free, but the replacement is just as suspect as the first one. You have had more in a row than usual, but it can happen.
  • edited July 2009
    I infer that your alternators are dying electrically, not mechanically due to bearing failure or some such.

    It's not quite clear to me how a battery can cause an alternator to fail and still test out OK, but I'd sure suspect that the battery might be the culprit because it is about the only thing likely to slam a big enough load on the alternator to damage it. Furthermore, if the battery is working properly it's not that easy for anything else in the car to damage the alternator without blowing fuses or bursting into flames.

    Maybe someone can suggest a failure mechanism and or diagnostics.

    In any case, batteries are not built to last forever, and I infer that yours might be elderly because you didn't mention replacing it. Replacing the battery will be cheaper than buying yet another alternator. I don't usually favor throwing parts at problems, but in this case, I think if it were me, I might replace the battery as well as the alternator this time.
  • edited July 2009
    Does anybody bench test alternators anymore? I would like to see one of these early failure alternators tested to see if they all died the same way.

    Bad diodes would suggest a bad battery or other excessive load caused overheating. If the "bad" alternators aren't really bad, then there's a wiring/connector problem. In the process of changing the alternator the wiring gets wiggled around and a loose connection gets temporarily restored.
  • edited July 2009

    I also suspect that the battery--particularly if it is the original--on this 8 year old vehicle is the actual source of the problem. Even if the battery is not the original one, by my standards this car should now be on its 2nd replacement battery. The battery and the alternator work synergistically, and a weakness in one will inevitably lead to the failure of the other.

    A possible scenario is as follows:
    The original failing alternator may have led to a weakening of the battery.
    Then, this weakened battery needed to be charged so much that it quickly overheated and killed the subsequent alternators.

    It is difficult to determine the exact cause and effect here, but since a battery is much cheaper than an alternator, and since I do not like to be stranded by a battery that fails without warning, I tend to replace my car battery every 4 years or so. I consider this to be preventive maintenance, even though it is not listed as such by any car manufacturer.
  • edited July 2009
    Thanks for all the feedback. I have only owned the car for a little over a year and have no idea when the battery was last replaced. I looked at the battery itself but the year/month sticker was not pulled off, however the years started at 2001 and ended with 2009 or 2010 so I am guessing that it is pretty old. The battery was tested but if it is requiring to be charged more often than the alternator can handle that would make sense and maybe the mechanics wouldn't see that on the systems check.
    I did have brand new, $300 alternators replaced each time, each with a lifetime warranty so I can have that part done for free. It would be nice on my pocketbook to only have to replace the battery.
  • edited July 2009
    Since the battery appears to be old I would replace it regardless if it is ok or not. It is good practice to replace the battery when a new alternator is installed if the battery is fairly old. This should keep the charging system going for a long time.

    The trouble you are having may be due a bad PCM or in the wiring if it controls the charge rate of the alternator. The shop needs to check to see if the wire for the battery sense voltage lead is working like it should. If the regulator thinks the battery voltage is low at all times it will make the alternator work harder than it should and supply more current to the battery than it needs to. This will cause the alternator to die an early death. It will be hard on the battery also.
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