Alternator failures--causes?

Good evening.

I have a 1998 Ford Explorer V6 with 172k miles. The original alternator
failed
in November, and I replaced it with a "premium" rebuilt alternator from
NAPA.
(The "premium" designation means that they install a new rectifier instead
of a
"good used" recitifier. I considered this an intelligence test.) This
alternator failed
a week ago. I returned it and they gave me another one.

What I am wondering is, could there be some other issue with the electricals
that is causing alternators to fail? Certainly it is no surprise that the
_original_ failed
with nearly 170k miles on it, and it is also possible that the first rebuild
was
faulty. But now I am worried that a few thousand miles from now I will
encounter
yet another failed alternator, perhaps when I'm up in the mountains rather
than a
few blocks from home. I want to make sure that there is not something else
wrong
that is causing alternators to fail.

I checked the voltage drops from the BAT connection to the battery (+)
terminal,
and from the alternator case to the battery (-) terminal. The drops were
0.08v
and 0.02v respectively. Those are acceptable I believe. Is there anything
else
I should be checking for?

Thanks
-Mark

On Sun, 21 Mar 2010 19:16:29 -0700, "Mark G." >
wrote:

>Good evening.
>
>I have a 1998 Ford Explorer V6 with 172k miles. The original alternator
>failed
>in November, and I replaced it with a "premium" rebuilt alternator from
>NAPA.
>(The "premium" designation means that they install a new rectifier instead
>of a
>"good used" recitifier. I considered this an intelligence test.) This
>alternator failed
>a week ago. I returned it and they gave me another one.
>
>What I am wondering is, could there be some other issue with the electricals
>that is causing alternators to fail? Certainly it is no surprise that the
>_original_ failed
>with nearly 170k miles on it, and it is also possible that the first rebuild
>was
>faulty. But now I am worried that a few thousand miles from now I will
>encounter
>yet another failed alternator, perhaps when I'm up in the mountains rather
>than a
>few blocks from home. I want to make sure that there is not something else
>wrong
>that is causing alternators to fail.
>
>I checked the voltage drops from the BAT connection to the battery (+)
>terminal,
>and from the alternator case to the battery (-) terminal. The drops were
>0.08v
>and 0.02v respectively. Those are acceptable I believe. Is there anything
>else
>I should be checking for?
>
>Thanks
>-Mark
>

How did the 'new' one fail?

What is the average charging output (use a clamp-on DC Ammeter?)

The concept that they 'use new rectifier' instead of a 'tested, good
used one' is odd... First, you have no idea where that 'new' rectifier
came from--and it probably came from china, where all crap like that
comes from, while the OEM rectifier was probably a much higher quality
unit.