What is it with cold weather and alternator's? I replaced my alternator last winter, and it just died again yesterday (it just started getting cold here). My battery light fades in and out (it actually went out completely before I parked it). I tested it with the meter and it's putting out no DC volts (DC read slightly higher with the car off rather than running) and the VAC reads about 25?! What do the VAC numbers tell you exactly? With these kinds of numbers I would think the my battery light would be constantly glowing.

I replaced it with an alternator from a chain store last year (I think a 55V remanufactured one, probably a cheapy). Still, I thought it would last more than a year. So, what is a good alternator that will last longer??
Is there anything else to look for (i.e bad battery) that would make this thing die after 1 year? My battery always seemed to hold a good charge, I never had to jump it. Could a bad ground be making the battery light come on/off or fade instead? Thanks...

Looks like the warranty on the alternator is up on Jan. 9. So, at least I lucked out there.
I see answers to why my alternator might die early here too:

http://www.peachparts.com/shopforum/showthread.php?p=755872#post755872

How good is your battery? Are you driving alot of short distances? Cold starting takes alot out of your battery. The alternator will work harder to bring it back up to charge. STAY AWAY from chain store rebuilds..... Replace it with a BOSCH rebuilt unit and your problems should go away.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

High VAC indicates diodes that no longer rectify the AC to a DC voltage the car can use. Usually what takes them out is a severe load on the alternator such as a combination of cold weather and severely discharged baattery. Yes, a poor ground can definitely be causing this. In fact, many alternator shops will tell you that is one of the main causes of alternator failure. Check/clean both the batt-chassis and the chassis-engine grounds. They are, after all, half of the circuit on your car.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Good point, I was going to mention that I am making mostly short trips (about 10 minutes at a time). Is 55V not enough for these cars in cold weather and short trips?
It did make it a year, so I probably don't have a major problem somewhere other than just an inferior alternator.

55V is about 4.5 times too much! It's a 12V system with a 55A alternator.

Okay, that's what i was looking for. AC current and no DC current means alternator is most definitly shot. I checked the wiring and grounds last year, but I will have to investigate them a little better this time.

Ooops Amps, volts... it's all just a bunch of electrons to me.

I got home today (15 min. drive - battery light was on along the way and flickering / dimming) and when I pulled in, I noticed the battery light was off, so I decided to check the voltage. It had 14 dc volts at the battery. Very nice. BUT, it also had 30 ac volts at the battery. That can't be good. Weird. Is that even possible? Could people be driving around in cars that are pumping both ac and dc current into their batteries and probably ruining them?

Yes, it's very possible to have 30VAC and 14VDC. The non-rectified AC voltage is about twice the DC voltage. You are looking at replacement/repair of the alternator due to failed diodes.

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Sam

84 300SD 350K+ miles ( Blue Belle )

If your un happy with chain store alternators take it to an alternator shop. If you find a good one they can work wonders for a reasonable price.

So, now I'm getting confused. As mentioned I got home last night and my alternator miraculously started working again. However, it was still putting out 30 volts ac current. So, I took the wife's car to be safe. The ac voltage on my car seemed odd, so I checked her car. It says 30 volts ac as well. We never had a problem with her car, so I suspect my meter is wacky or I'm doing the ac voltage test wrong. My meter settings are 200 or 600 AC V~... I don't think it's reading millivolts. I put the red lead on the pos. battery term. and the black lead on the neg. term.

Right now I'm thinking that I have a bad ground or wire somewhere...

Read post #9..........again.

The fact that BOTH cars (one relatively new) are putting out the same 30 VAC at the battery makes me suspicious. I think I'm doing something wrong here... Unless of course I got lucky and caught a bad alternator on her car too
Electronic's should be easy, but they sure frustrate me...

Has anyone tried to locate the internal hardware to rebuild these alternators. I remember in the old days buying the stuff to rebuild my alternator in my 914. Can you get the diodes, or maybe just the whole board? Maybe I'll pull my 65A appart this weekend to see if I can find the failed part. My voltage is fine at the battery until I start the car and it goes down a half a volt or so. Took it to the autoparts store and the found that its only putting out about a half a volt. I plan on selling the car and what to put as little $$ as possible into it.

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Currently driving a very clean 1985 300SD from the West Coast.

Okay, my cheap Wal-Mart muiltimeter is goofy. I tested the battery on my Jeep now, again it reads about 30 VAC, there's no way all my cars have bad alternators. The battery reads about 30 VAC with the engine off too. I tested a 1.5 volt battery, it reads about 2.8 volts on the ac setting. Somehow, when you put the meter on ac voltage, it reads the dc current and just about double's it. Wierd. Can anybody tell me a decent, yet fairly basic/simple mulitimeter to get? I'm thinking my alternator is ok, I just have a bad connection somewhere...