I'm trying to help my parents out with their Buick which is having voltage trouble, It's been awhile since electrical class so here's the question. I put a new battery in around October/November and the car was fine untill recently the battery kept going dead at night. Today I was checking the alternator and I put the positive lead on the number one terminal on the plug that goes in the alt and put the negative on a ground and with the key switch and everything else "off" It's showing voltage there. Doesn't this mean that the diodes are bad and voltage is "leaking" back with the car off? I just want to make sure the battery isn't a dud. Also when I have the jumper cable on from my car the alt is putting out 13v but when I pull the cables it goes down to 3.6 even though the batt still has about 6 or so. thanks, -Jon

 

Buick.org?

 

John, before you can test anything, you need to fully charge the battery. Check ALL the main power connections, at the battery terminals, at the starter, at the engine and body grounds, and if the cables use clamp on style terminals take them off the cables and check to be sure the cables are corrosion free. If you find corrosion on the cables, clip them back until you get clean copper, then clean and re-install your battery terminals, or put on a new set. Clean all your connections, and make sure they are tight. Voltage across the battery terminals on a fully charged battery should be between 12 and 13 volts. With the engine running, the volage across the terminals should be around 14 to 14.5 volts.

If you get less than 12 volts across the battery terminals, disconnect the battery cables and retest. If there is a significant difference with the cables disconnected then look for a drain somewhere in the electrical system (could be a bad alternator). If the battery is below 12 volts with the cables disconnected, it is not fully charged, have it charged / load tested.

If battery voltage is good, but voltage with the engine running is below 14 volts, look for alternator problems. Perhaps slipping belt, bad connection, or failing alternator.

DO NOTE that poor connections at the battery terminals will cause slow drain of the battery, and many other symptoms that could point toward the alternator.

 

You're making it too complicated, I suggest that you take out your alternator... bring it to Autozone have them run testing on it. Then you'll know exactly whether it's good or bad.

Don't even brother thinking you could fix those alternator yourself. Ideally, they seem easy but it's a real pain taking it apart without damaging anything.

Also, don't forget to disconnect your negative battery terminal before installing/removing that alternator or you'll fry your alternator again.

 

Bingo. I would have given the exact same suggestions.

 

well I put one together in school and it actually dished out 90amps but that was years ago. And thanks for the advice but I'm not going to do all that stuff to my parents haggard buick when it's probably just the alternator. and as a final note I hate autozone and only shop there because of the warrantys. Doesn't really matter anymore because I'm going to buy one tommorow and if it work it works. Thanks again guys -Jon (hope I didn't sound like too much of a jerk)

 

If you park your car at night only to come out in the morning to the battery dead then it seems you have a pretty strong draw somwhere. do you have
1. an aftermarket alarm
2. do you have a high power stereo and or amp.
these things can prematurely wear out a battery.
ALSO I HAVE TAKEN alternators to auto zone and one time got a kid who didn't know what he was doing andj told me I had a good alternator when I had not. So BEWARE

 

Yeah I replaced the Alt today and now it's putting out almost 15v so I think she's good to go.

 

Sounds good!

 

Glad this all got sortedAs an Electronics Engineer I would really like to know the mechanism involved in achieving that - assuming you not actually talking about the inability of the alternator to charge the battery properly under those conditions.

Its my contention that a bad battery connection is not far from actaully removing the terminals from the battery altogether, so how is a drain gonna happen with no current flowing (assumung a car's electrical system is otherwise ok)?

 

More fun with alternator problem...I put it in and it was fine drove it about 30 miles with no trouble except I noticed that the power wire for the alt. was getting really hot to the touch. My mom drove it later on that night, called and said the check engine light was on again and after turning it off it wouldn't start again. I jumped it and it started right up no warning lights, followed the car for about a 1/4 mile and the headlights were barely on, no acceleration and the battery died again. I was thinking when I bought the new alternator it had a bolt on the backside of it that wasn't on the old one. Maybe there was supposed to be a ground strap on there that fell off the old one? (haven't checked yet because the car is on the side of the road somewhere)

 

yeah lvr, that doesn't make sense to me either

 

It sounds like you might have a short somewhere. Do you have a multimeter? If so, check the resistance between the pos. and neg. terminals. Just an idea.

 

Voltmeter man ....................... use it before you assume anything with the electrical system is ok

 

whoa, calm down bud, I did use a voltmeter, turns out there was a short which fried the power wire running to the alt.... ran a hotwire from the battery and she's good to go.

 

Quite calm thanks .................. just fail to understand the sequence of events here .................

1. "Short" that fried the fat cable between the alt and battery? ............... when did this "short" appear and what exactly was the cause?

2. "Any "Short" on that cable causing a huge temp rise in the cable would have been detectable with a voltmeter on both the battery and the alternator ....................... so I guess is the question is if you used a meter what did you measure there that made you think its OK?

3. "Short" on that wire to the extent that the wire was totally killed and "burned off" implies a ton of current flowing way over the rating of the cable (my guess around 100A rating) ........................ question is what supplied the current - the battery or the alternator or both? ................... my thinking is neither will be reliable now that the "short" has been fixed.

What is the battery terminal voltage after its been standing a night?
What is the alternator's output terminal voltage with the lights switched on?
What is the battery voltage under that condition?

Just for the record:

Not trying to bust your cahonies but the whole story and posted facts just plain doesn't make technical sense at all, so as a documented experience for somebody to learn from, its currently completely useless IMO

 

okay, you seem like a technical enthusiast so I'm going to give you every little detail here so you can stop loosing sleep over this. Parents tell me, car won't start after sitting at night. Car started when jumped. First thing I did...take multimeter from harbor frieght, selected the "Volts DC, 20" option. I put the positive lead on the "power in" on the alternator. Then I put the ground lead on a good frame ground spot. With the engine "off" the voltage read about 5.3 volts. With the engine running it showed about the same. I thought to myself, "this is unacceptable". I then began my reasoning that if the voltage regulator or the "diode trio" wasn't functioning proporly that voltage would be allowed to go through when the alternator was in a static position. I then purchased a new alternator. The only problem here was that the new alternator's clocking was backwards so after installation the wires would have to reach quite a bit further. To my suprise no wire had to be added. After driving the vechicle for a while I recieved a "check engine" notice from the machine. I pulled over and noted that my crimp had come off of the power input. I put it back on and later noted after driving that the power wire was a little warmer than one would think it to be. Since the out put of the alternator was normal and there was no fire and or smoke my instincts told me that there was nothing out of the ordinary, and after long trips on the highway we all know that engines tend to heat up quite a bit. common sense yes? Well when I attempted to recrimp the wire it happened to bump into the casing on the alternaor causing a "short to ground" which raised the tempature of the wire phenominaly. After some smoke was emmited I checked the wire for damage and all looked okay. My mother drove the vehicle about 2 miles away or so later that night and called saying the check engine light was on and that it would not start again. I drove my Maxima to the scene and jumped the vehicle telling my mother "let's get it home and I'll look at it again". Well the car made it about halfway and refused to continue. Now..mind you I didn't have my harbor frieght multimeter with me at the time. So the vehicle was left on the street in question overnight. The next morning I returned to the scene and applied my meter to the alternator power source. Positive lead on the power in and negative lead to a trustworthy ground. Now we had 0 volts in to the alternator. Now I sensed that the connection had been severed due to the undesirable events the night before. I took a few feet of ten gauge wire and ran it from the postive battery terminal to the power in on the alternator. We now had about 14.6 volt connection in good working order and the vehicle was charging like a champ. Now was that power wire doomed from the begining anyway with its getting hot tendancies? you be the judge. As we all know, one of the drawbacks of an alternator is that it needs power to make power. Induction is the key. I hope this helped you understand and as of now I hope this thread can be put to rest as the problem has been taken care and now mommy dearest can drive her machine again.