Find or purchase a clamp on amp meter that will read both AC and DC
amps. Turn on enough loads so that the alternator is generating at
least 50% of it's rated load. Measure the DC amps and the AC amps of
the alternator output. The AC current should not exceed 15% of the DC
amps. If it exceeds 15% then you have a bad diode or stator winding.
In many cases you can not get 50% of rated output if you have a bad
diode.
John




On Sun, 05 Dec 2004 22:42:57 -0500, Jonathan Goodish
wrote:

I know that this is another frequent topic, but I'm hoping that someone
can help narrow this down for me.

I have a rebuilt Chrysler alternator (from Electrosystems) on my
Cherokee that was installed about 400 hours ago. However, I am
experiencing alternator whine that varies with engine speed, but which
disappears completely when I turn off the alternator side of the master
switch. In addition, increasing electrical load seems to make it worse.
I have replaced the filter capacitor on the alternator output with a new
one (15uF) and it doesn't seem to have made much of a difference (the
filter is grounded to the alternator).

My mechanic took a look at the alternator at the last annual inspection
and thought that the cooling fins were backwards (auto style, not
aviation style). Not sure if that's normal for the Cherokees or not,
but I can't believe that Electrosystems would do it wrong.

How long should I expect this alternator to last? Does this sound like
a rectifier problem that would warrant replacement of the alternator
after just 400 hours? Could it be a regulator problem? Any suggestions?



Thanks,
JKG