Why am I frying alternators?
 

My car had the original Alternator until a couple of years ago, although it had produced pretty low (12.75 or so) voltage for years and prolly had bad diodes too. I replaced it with a bosch reman about 1.5 years ago. Car was totally dead last week (no I don't know why, I blamed my kids but maybe that was a crime of oportunity). So I charged at 10 amps all night, and it still was drawing 3 or 4 amps when I shut off the charger to go out of town. I disconnnected the battery for the upcoming departure, and when I got back I charged several more hours with battery disconnected. Well now I only get about 12.0 or 12.1 volts on the console meter. It used to read 14+ all the time. Does anyone make a NEW alternator for this car? What could I be doing to cause this to happen? This is the third diode killing incedent in two years. I have read you can kill alternator diodes by overcharging. Was all charge from 10 amps and on down "overcharging?"

I seem to remember a thread about the studs inside the alt. touching the cooling cover. Possible culprit.

Anybody concur?

Try this: http://forums.pelicanparts.com/showthread.php?s=&threadid=132735&highlight=altern ator+cover+bolt

I don't know who found the original problem, but I saved it. Here goes:

WARNING! - Bosch Rebuilt Alternators!!

I've been fighting the last week trying to resolve an alternator light that wouldn't go out - even after installing a rebuilt alternator, new regulator, changing the alternator light to 2W, and checking/cleaning all connections.

The source of the problem was only found after trying three Bosch AL75X Rebuilt Alternators. Based on BAP Auto, this is the Bosch replacement alternator for the 914/2.0.

The problem is with the design of the black cover that fits on the rear of the alternator to cool it, and the recent rebuilt alternators. This back cover does not come with the rebuilt, and must be removed from the core alternator and installed on the rebuilt - hence the problem.

The three-wire connector that caries DF, D+, & D- to the relay board is in one bundle, and the B+ wire that goes to the starter solenoid is a single separate wire. The AL75X has two studs coming out of the back of the alternator. One stud is taller than the other to permit connection of the B+ red wire.

http://forums.pelicanparts.com/uploa...1096416680.jpg

Both studs on the AL75X have a large washer with an index tab, than a small washer, then the nut. The smaller stud (opposite the post for the B+ wire) is positioned such that the large washer will short against the cover when is screwed down with the three small nuts.

This is the source of the problem, and will not be apparent unless you check continuity between the red (B+) wire and the alternator case as you assemble the cover. The flat on the inside of the cover will hit the edge of the large washer.

http://forums.pelicanparts.com/uploa...1096416742.jpg

The solution is to 1) remove the large washer, or 2) snip part of the washer off - opposite the indexing tab.

http://forums.pelicanparts.com/uploa...1096416840.jpg

Then when the washer is installed and the cover is in position, it will not short against the washer.

http://forums.pelicanparts.com/uploa...1096416895.jpg

It is also suggested that once you have the cover assembled that you use your volt-meter to check for continuity between the red (B+) wire and the silver body of the alternator. There should be none. Hope this helps someone else in the future.

That was pretty-much it. I wouldn't place a whole lotta faith on the console voltmeter, although it reading 14+ volts is a bit high. You're picking up a short through the alternator some how.

Also you failed to mention if you have ever replaced the voltage reg. If it gets stuck it can drain the battery and cause charging problems. just my .02

Wow- great replies. I saw Rouser's great detailed evaluation when I searched. I did replace the VR a couple of months ago. Would it show this kinda response if it is hosed (in your experience)? I probably gotta do the new reman and fix it before I put it in, but I'm grasping for ideas here- something short of replacing it again, although if I do and fix it per the instructions it becomes one less potential problem....

Scott...

Don't put too much faith in the VDO voltmeter in your console. They are not accurate. Use a Fluke meter if you want accurate readings. My VDO is off by over 1.5 volts.

Thats interesting that the bolt hits, i had lots of problems myself with alternaters....how about using some silicon sealant or glueing a thin rubber groment on the tin peice to make sure they don't touch...

Here is a Factory Altenator with Air cover removed
http://forums.pelicanparts.com/uploa...1096488784.jpg