What causes alternators to fail??

[BeauBlues]

Ok, I'm getting really frustrated here, so I need all the advice I can get. My alternator failed a month ago. I had previously had this same alternator rebuilt at a rebuilder about 3 years ago. So I took it to them again. They said we have have a rebuilt one here ready to go, you just give us your old one. I agreed and paid the $75 and went home to install it. My old alt was a paris rhone, this new to me rebuilt one was a valeo. The install went smoothly and the battery was a getting a good charge about 13.8v.

Anyway, this last thursday, I got in the car to go for a drive and the alternator light was on. I pull back into the driveway and check to voltage at the battery and read 12.2volts and got no change with raising to rpm. I took some time to fully investigate and check the voltage at the starter, same thing. So I took the alt out and checked voltage at the alt wires. ALL was good.

So I hopped in my parts getter and went to the same shop, they remembered me and I said the alt is not working. Their first response was "NO NO NO there is something wrong with YOUR car" I just about blew a nut! I said absolutely not. I just checked everything, its all fine! They bench tested it and it was giving a good charge. I couldn't believe my eyes. I told them, I know I am not crazy, you need to check it thoroughly. They said call back here in an hour.

Called them back and they said the diodes burned out. So then I asked, why did they burn out? They again gave me the response that it's most likely MY car. They asked if I have a big sound system. I said no. The only electronics I have is the stock stereo, the headlights and the engine. I got home and reinstalled the alt. Everything went back to normal again. Getting a good charge of about 13.8 ish volts. I drove it for a while on that same day of thursday. All is fine.

So I went out of town over the weekend and get in the car when I got back. Guess what! The freaking alt light is ON AGAIN!!! Not even three days!!! Reading 12.2 volts at the battery. Today is sunday, so I can't do anything today. Somebody please tell me what the hell is going on. I cant possibly think of anything that is wrong with my car to cause this. I have not messed with a single thing on my car that is related to the charging system. Is this a case of shoddy workmanship from the rebuilders?

[Wil Ferch]

Junk French workmanship....hide it inside the fan shround where it gets really good and hot ( and heat soaks)....throw in some questionable rebuild quality...and then marry that to garage queens that don't get driven very much and put a big "up-take" strain on the alternator ( working its poor guts out to top-off a battery).......

...and ya got your answer as to "why" .....

[Paulporsche]

Wil,
So are you recommending (as you mentioned in another recent post) to go w/ a smaller battery, ie one w/ a lower Ah rating? Can the diodes be "increased" somehow? Obviously, he could drive the car more often, or use a maintainer anytime it is garaged.

[burgermeister]

Maybe you just need a new battery? If your is almost dead, it could really overtax the alternator every time you start it.

[Jim Sims]

Disconnecting the battery with the engine running can blow a diode. If there is an intermittent connection in the alternator to battery circuit wiring it can be the equivalent of lifting the battery cable with the engine running.

[dshepp806]

Heat or load issues...killers...oh yeah:

and "mother time"....

Best,

[BeauBlues]

Thanks for the replies so far. My car is not a garage queen by far. It is my committed daily driver. I have not fidgeted with the wiring to the charging system at all. And the battery only a couple years old and starts the car very healthy every time. I'm seriously thinking of getting a bosch alternator and be done with it.

[Formerly Steve Wilkinson]

Paris-Rhone? A famous high-quality manufacturer? An incredible alternator state-of-the-art advancer? I don't _think_ so.

[Jim Sims]

"I have not fidgeted with the wiring to the charging system at all."

How did you remove/install the alternator without disconnecting the wiring to the alternator?

Wiring connections (especially Porsche grounds) can loosen/corrode over time due to over heating, vibration, road chemicals and exposure to the atmosphere - they don't have to be"fidgeted with" to fail.

Bosch alternators (now possibly made/rebuilt in Brazil, China or who knows where) can blow diodes too.

[Wil Ferch]

Certainly it helps to have a battery smaller in size than the Mercedes-Benz diesel battery ( 88 AH) that normally is installed in mid-80's Carrera's. Then, have a "chipped" battery maintainer when the car is off in the garage ( Schumacher-style float-charger)...that helps too. Don't know if it helps but after a hard run I usually pop the deck lid and let it cool that way. Although LorenB doesn't agree...I run the HUCO brand replacement voltage regulator since it has a much larger heat sink than the stock French piece. Loren says it's junk but it's been serving me well for a number of years now....

[gerrygug]

Spring for a new Bosch unit. They are expensive but if you are on your third rebuilt unit in three years and still have a problem it would have been cheaper in the long run.