Can An Alternator Run Down A Battery??

[1990 Lumina Euro Coupe]

So I'm having trouble with one of the Dubyas running a battery down after driving for a while, or sitting for a period of time.

 

Thinking it's the battery, I take it to Autozone to have it tested. I had already pulled the switched lights(trunk, hood, overhead) to make sure they were not staying on and draining it. They say the battery is fine

 

The fellow suggests that I allow him to test the alternator to see if it is putting out current.

 

He tells me that it is, but says that it could still be the problem, because they have "something inside them that when it goes wrong, it runs the battery down." He could not tell me what that "something" was, however.

 

I have never heard of a working alternator actually draining a battery, even when the car is being driven.(It's not killing the battery, BTW the battery can always be charged back up with no problems.)

 

Has anyone ever heard of this?

[digitaloutsider]

I'd check the grounds, first. I don't see how an alternator could DRAIN a battery. It can not charge one, but not drain one..

[DaveFromColorado]

if the diode bridge goes bad, it *may* be able to short to ground, but I doubt that's it, I think god910 posted something about how to check for the current draw, just pull the neg. battery cable, and put your volt meter in line from the neg. terminal, to the neg cable, and watch for the current to drop as you start pulling fuses, once it drops off, you know which circut is causing the problem.

 

someone please correct me if I'm wrong with any of that...

 

--Dave.

[GnatGoSplat]

I had a bad alternator that did just that.

 

Something happened to the diode bridge... maybe a few shorted. When I had my alternator tested, the guy at the auto parts store said instead of producing current, it seemed to be consuming current.

[93vinX]

well you alternator reuires power to turn the fields on so if the ignition swith was giving it power it could pull power

[amcjrb]

I have had this happen, it was a bad rectifier bridge. On that car (not a GM, but it did have a delco alternator) the alt light stayed on all the time, even with the ignition off. IT wasnt really bright, but it was on. BTW< it was cheaper to buy a rebuilt alt than to by the parts and fix it myself.

[Euro]

I think it can actually run down the battery. On our 84 Monte Carlo SS the alternator belt and fan belt snapped on the way to our first cruise night :? so we had to have the alternator run off the battery. I was told that the alt. can wear down the battery if it has to.

[Pselus]

this is EXACTLY what's happening to my car.

when I got the car it was having trouble starting, but you could just jiggle the key and it would start fine...so we thought it was the starter...well to be safe we got a new starter and a new battery...it worked fine for about 6 months then all of a sudden it comes back with a vengeance until I can't start my car ever without a jump (however with the jump it starts instantly and I can still do the radio, windows, electric top fine)...so I go get my battery tested at O'Reilly's (like Autozone) and they say "yep, bad battery"...so I buy a new one...well it's not even a week later...and my car is having trouble starting again...it's not bad enough that I need a jump yet...but it degrades quickly...

so here I am broke and I think I'm gonna need a new alternator

[phantomshado]

do not buy a reman alt. I can't stress this enough. Buy a new one. its the only way to go.

 

3 remans and 1 new alt later....you tell me whats up.

[93CutlassSupreme]

do not buy a reman alt. I can't stress this enough. Buy a new one. its the only way to go.

 

3 remans and 1 new alt later....you tell me whats up.

 

:withstupid:

[Z34door]

if you go the reman route... buy a BOSCH........... lifetime warranty. BTW is it a 3.1 of 3.4......... if its a 3.1 you're golden........ if its a 3.4 have fun.

[Z34door]

im stupid....... 90 euro...... LOL has 3.1 buy a bosch..... you'll be happy you did. i have one and have never had a problem

[excelsior]

i have had it drain my battery b4 :x

[93CutlassSupreme]

if you go the reman route... buy a BOSCH........... lifetime warranty. BTW is it a 3.1 of 3.4......... if its a 3.1 you're golden........ if its a 3.4 have fun.

 

BOSCH makes some of the most sorry piece of shit parts i've ever used