1997 Venture - Repeated Alternator Failure

My 1997 Venture with 98K miles has experienced repeated alternator failures. The vehicle has the Valeo 105A alternator. I replaced the original unit 2
years ago with one from Napa. It lasted until January 2007, though I experienced problems well before I replaced it. The problem is most evident when I first start the vehicle, it runs fine and there is no belt noise. Then 20-30 seconds later, the belt begins to sequel. When you increase the rpm's, the belt sequel gets louder until the sequel ceases. Then you will not hear the sequel the rest of the time the vehicle is running. I know that the belt is slipping on the alternator...you see rubber shavings on the face of the alternator, around the pulley. I then installed a new alternator in January and it showed signs of failure so I replaced it last week. The alternator showed a I/F failure, though I believe that it was an intermittent failure, because I had to have it tested again before I was given the replacement unit, the test showed that it was in good condition. With the new alternator, I only use it for a few days, when I again heard the belt sequel noise. I have not driven the vehicle since.
I cannot seem to figure out what is causing the alternator to behave in this way. I checked the ground connections and I believe that they are solid. I have a new battery and a new belt. The tensions looks to be good....it takes plenty of force to move it out of the way to install the belt. The belt routing is correct as well. Is there a connector (other than at the alternator) that may be corroded, that could be causing this problem. Any assistance is appreciated....I'm stumped on this one. Thank you, Joe
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Joe Guarino wrote:

about starting it, when it squeals shut down and pull the belt and check it.
--
Steve W.
Near Cooperstown, New York
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Replace the belt pensioner. It is probably not tensioning the belt properly.

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My guess would be that the belt tensioner is probably failing.
The alternator is under the heaviest load just after start up as it recharges the battery from sitting and from the load of starting.
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Can a weak tensioner cause an alternator to fail? Is it possible for the alternator to overheat? Thank you, Joe

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