Not Another Alternator Q!!!

[obsolete]

So my car has been sitting in the cold for a few winter months and, sure enough, couldn't get it started. It would crank, start clicking, and just die. I was able to jump the car and the voltage on my timer was showing 14.3 or so. I was driving/idling for almost 2 hrs before I was able to get a sears tech to take a look at it and when they did the load test on the battery, it would drop to around 8 volts. So I got the bad battery replaced with a new one. Then they tell me that my alternator failed and I would have to get it replaced. When I was driving home, the volt read 13.7 all the way.

Hopefully you guys could school me, but if my alternator was dead, wouldn't the car die again after i've jumped it? All my lights, dash, electronics were fine and the car ran w/out any problems. Anyone know the likelyhood of an alternator test being wrong or inaccurate? The battery light didn't even come on. I replaced the alternator not too long ago with a used one. The brake light is lit though and will not go away, but I think that might be from fluid level.

[Sileighty_85]

yes if your alt was bad once the car used up the the power from the Battery the car will shut off, 13.7 is a normal voltage/charging rate for these Alts.

It is possible for your alt to be good and fail a test, Some testing machines are crap and just plain suck I had two of my SR alts tested and they both failed brought them to another place one passed other one failed, we did the test mulitple times, the one that failed twice is on my car now and Ive never had a problem.

A good quick way to check your alt is start the car and pull the Neg. (-) terminal if the car dies you need a new alt

[Mangudai]

Isn't that dangerous to you and your car?

[motonagam]

A good quick way to check your alt is start the car and pull the Neg. (-) terminal if the car dies you need a new alt

That's not a good idea... you'll cause a voltage spike in the electrical system and fry sensitive electrical components like the ECU. If the car dies, then it could be because you burned up the ECU.

[lazierhobo]

i have pulled the battery from my running car several times, and had zero problems.

if your seeing more than 12 volts when you measure voltage across the battery terminals while the car is running, then the alternator is functional.

the voltage being used by the electrical system while the car is running is around 14 volts and comes from the alternator, so im not sure how you could make the voltage spike by removing the battery.

[motonagam]

i have pulled the battery from my running car several times, and had zero problems.

if your seeing more than 12 volts when you measure voltage across the battery terminals while the car is running, then the alternator is functional.

the voltage being used by the electrical system while the car is running is around 14 volts and comes from the alternator, so im not sure how you could make the voltage spike by removing the battery.

A battery is like a voltage stabilizer or filter to the pulsating DC produced by the alternator. It absorbs the the excess voltage from the alternator. Disconnecting a battery while the engine is running can destroy the sensitive electronic components connected to the entire electrical system, or the charging system itself because the peak voltage can rise to 40 volts or more. You've just been lucky so far that the car still runs when you disconnected the battery while engine running.

[obsolete]

Ok, left the car sitting for a few days and she started up just fine. feeling more confident that there is nothing wrong with the alt. I put some brake fluid in and the brake light is out now. My tt says the voltage is 14.1 while engine was running. and I will not pull the (-) cable out while car is running. just doesn't sound safe.

[Skaterjunky8]

If you got 14 volts at your battery then the alternator is cherry dont worry about it. If you start to see that number decrease over the days, like friday its 13.5 then on monday its 12, then your alternator took a shit on you. Otherwise dont worry, and yes avoid pulling the terminals while the car is running, although effective, very dangerous. The one time you try it and it does fuck shit up, youll be int he middle of teh desert working on your friends car, and he will leave your ass there for the voltures after the tow truck picks him up

[racepar1]

yes if your alt was bad once the car used up the the power from the Battery the car will shut off, 13.7 is a normal voltage/charging rate for these Alts.

It is possible for your alt to be good and fail a test, Some testing machines are crap and just plain suck I had two of my SR alts tested and they both failed brought them to another place one passed other one failed, we did the test mulitple times, the one that failed twice is on my car now and Ive never had a problem.

A good quick way to check your alt is start the car and pull the Neg. (-) terminal if the car dies you need a new alt

On every thread about alternators everyone keeps referring to voltage. When are you guys going to learn that voltage means nothing!!!??? I have seen plenty of bad alternators that read over 13 volts. It is the amps that actually charge the battery. Clean all your cable connections and have someone re-test the alternator somewhere else. To test an alternator the machine applies a load to the electrical system and measures the amperage being put out by the alternator. And NO the car will not always die when you disconnect the battery if the alternator is bad, DON'T LISTEN TO THAT!

[ichibans13]

Once the car is started, the battery is never used again. The car runs off of the alternator. Plain and simple. If the alternator is going bad, then the car will die. The only purpose of the battery is to turn over the starter so you can start your car. And if you want to turn on your radio/lights/accessories without starting your car.

Pulling the terminals off of the car will not do anything to you. Especially if you do it with only one hand and have your other hand not touching anything. Now if you were bare foot, standing in a puddle of water, gripping onto a bare piece of metal connected to a grounding point and tried to pry off the positive battery terminal with a piece of metal, then you might be putting yourself in a bit of danger.

I swear you wont kill yourself. I've been working on electronics for nearly a decade. You wont even die if take a wrench and touch it to both terminals.

Pull off the battery terminals. Turn on your lights, stereo, anything that draws power, and either let it sit or drive it around.

Otherwise, go to the junkyard and get a new-ish alternator. It takes 15 minutes to swap one out.

[racepar1]

Just because the alternator is not putting out enough amperage to charge the battery AND run the car does not mean that it is not putting out enough amperage to JUST run the car. You are still wrong, I don't care how long you have been "working" on electronics. Why would someone who works on electronics reccomend a used alternator anyways? It is probably bad too! And if you are really worried about shocking yourself just pull off the negative first, really you should do that anyways.

[Mangudai]

So how do you test an alternator? What are the contact points with a multimeter?

[racepar1]

You CAN'T properly test an alternator with a multimeter! That's why they sell battery/alternator testers.

[ichibans13]

Just because the alternator is not putting out enough amperage to charge the battery AND run the car does not mean that it is not putting out enough amperage to JUST run the car. You are still wrong, I don't care how long you have been "working" on electronics. Why would someone who works on electronics reccomend a used alternator anyways? It is probably bad too! And if you are really worried about shocking yourself just pull off the negative first, really you should do that anyways.Nice quotation marks around the word [working]. Was that supposed to hurt my feelings? I've spent the last 8 years in the Air Force repairing F-15 electrical avionics equipment. I do fix electronics, but I dont claim to know everything. I was offering my advice. If he doesnt take it, I promise you, it wont ruin my day.

Just because its used, doesnt mean it wont work properly. Otherwise used cars would never be resold. Have you done a motor swap, or helped someone with a motor swap? I hope not, if your opinion of used parts is that they are all "probably" bad. If his results rest on your "probably", I dont forsee him making any progress. My suggestion was just that, a suggestion; I never said what I spoke was gospel.

[Mangudai]

You CAN'T properly test an alternator with a multimeter! That's why they sell battery/alternator testers.


Thanks for the reply. One last thing if you dont mind? How do you check if the wires how a good connection? I ask because I may have a bad alt but I don't know how to check the wiring.

[racepar1]

Nice quotation marks around the word [working]. Was that supposed to hurt my feelings? I've spent the last 8 years in the Air Force repairing F-15 electrical avionics equipment. I do fix electronics, but I dont claim to know everything. I was offering my advice. If he doesnt take it, I promise you, it wont ruin my day.

Just because its used, doesnt mean it wont work properly. Otherwise used cars would never be resold. Have you done a motor swap, or helped someone with a motor swap? I hope not, if your opinion of used parts is that they are all "probably" bad. If his results rest on your "probably", I dont forsee him making any progress. My suggestion was just that, a suggestion; I never said what I spoke was gospel.

A used electrical part like an alternator is just a bad idea, so is the cheap stuff from vatozone, pep boys, etc.... Why waste your time replacing a bad part with another part that is likely to fail in a short amount of time? I'm kinda spoiled since i'm a mechanic because I get parts for WAAAAAAYYYYYYY cheaper than most of you can. I quoted "working" because LOTS of people define "working" as doing it on their own cars in their free time, that does not qualify as "working". For the record I AM doing a CA18 swap for my buddy as we speak and I am going to reccomend that I have my re-builder do his alternator as it is COVERED with corrosion and the bearing is noisy. I just want people to know that that is not the RIGHT way to test an alternator. Just because it passed the test that you described does not mean that it is good.

Thanks for the reply. One last thing if you dont mind? How do you check if the wires how a good connection? I ask because I may have a bad alt but I don't know how to check the wiring.

Start by ohming the wires. If the resistance is high then there is a problem somewhere. The BEST way to test battery/alternator wiring is to do a voltage drop test. You must send power through the wire and measure the drop in voltage across the wire. Ohming the wires out should be good enough to tell you if there is a problem though. If the connections are dirty though an ohm test may not show it as the test lead of the multimeter has a point on it and will penetrate through the corrosion and make a cood contact.

[ichibans13]

No worries. I dont base my electrical experience based on backyard motor swaps.

Another good thing to help out to ensure you're making a good connection is to throughly clean the connectors going to the alternator. Get a wire brush and clean the posts and the contacts. Corrosion can cause a problem and be one hell of an electrical gremlin.

[racepar1]

^^^ Absolutely! My buddy had a misfire that him and my other buddies just couldn't figure out. He was actually going to do a motor swap just because of the misfire since it was frustrating him so bad. I pulled off the injector connectors to ohm them out and the terminals were COVERED with deposits. I told him to take a wire brush and clean all the connections for the major engine sensors. Car ran bitchin after that!