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Old 12-06-2013, 01:41 PM
 
1,728 posts, read 2,920,116 times
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Quote:
Originally Posted by RayinAK View Post
The reason why it kept running is because your car's battery had sufficient power left. But turn the headlights and the heater blower on, and the battery dies pretty fast, at which point the motor stops running. The motor stops running because it loses power to the ECM (computer), which in turn can't power the spark plugs, fuel pump, and the injectors.
How Does An Alternator Work - Charging System Alternator - Alternators Defined

A couple of years ago on my way home from work, the Honda Civic I was driving stopped running while driving. It's dark almost all day and night in Alaska, so I had the heater and headlights on. All of the sudden the lights dimmed and the motor stopped running, so I immediately pulled to the road's shoulder. The battery was completely dead, and I kew that if the alternator would have been running properly, the motor should have continued running.

But I had a battery jump starter with me, so I connected the jump starter to the battery, tucked in there engine bay so I could close the hood, turned it on, and started the car. I made sure that only the headlights were on (turned the blower off), and drove home about two miles away.

My former job required me to assemble and test alternators, inverters, and aircraft generators. I did this for 20 years, and then retired.
I know cars dude. i was just pointing out alternator and/or the battery supplies power to everything. they just help each other out in the long run
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Old 12-06-2013, 09:18 PM
 
447 posts, read 559,326 times
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It does not matter how old the battery is as you cant call it bad because of its age. Its really very simple to just have a tech who knows what he is doing check it. Other wize you will be guessing. The car can run on the battery if it has enough power to keep it running but if the alt is not charging then once the battery is run low enough the car will die. If you jump a car with a dead battery and get it running and the alt is charging then yes it will keep running with a weak battery.
Is the alt always charging when the car is running. Basically yes but the alt is controlled by a reg that turns the field circuit on and off. When volts gets high enough the reg turns the field circuit off for a very fast time. then when the volts drops below setting the reg turns the alt field back on. This can happen 20 times a secong or more as its done so fast you wont see a change in light brightness or anything while running. Just have a good tech check it out as it cant cost to much and once he tells you what it needs you might replace the part yourself. But why guess and maybe waste money ? Ron
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Old 01-07-2015, 04:25 PM
 
1 posts, read 4,758 times
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I brought my battery about a year ago but lately i have had to jump it to get her started. Wear could be the issue because she's not totally dead all the lights and etc..still work.
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Old 01-07-2015, 07:29 PM
 
Location: Phoenix, AZ
1,070 posts, read 2,233,643 times
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Rare for a 1 year old battery to die, but I've seen it before. I'd put my money on alternator though. If the battery isn't charging enough when the car is running, it'll continue to die. Like I said in my post last year, take it to an auto parts store (O'Reillys, Autozone, Napa, Canadian Tire for our northern friends...). They'll check it for free.

Side note, because Pep Boys has an actual shop (with real mechanics, and shop insurance), they'll charge for things like battery changes (but I think they'll still check it for free). O'Reilly's and AutoZone will swap the battery for you for free (though the employees do appreciate small tips!).
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Old 01-10-2015, 08:33 PM
 
Location: The Circle City. Sometimes NE of Bagdad.
17,481 posts, read 18,634,440 times
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Quote:
Originally Posted by cab591 View Post
Rare for a 1 year old battery to die, but I've seen it before. I'd put my money on alternator though. If the battery isn't charging enough when the car is running, it'll continue to die. Like I said in my post last year, take it to an auto parts store (O'Reillys, Autozone, Napa, Canadian Tire for our northern friends...). They'll check it for free.

Side note, because Pep Boys has an actual shop (with real mechanics, and shop insurance), they'll charge for things like battery changes (but I think they'll still check it for free). O'Reilly's and AutoZone will swap the battery for you for free (though the employees do appreciate small tips!).
I dunno, I was at Pep at Pepn Boys last week to get new wipers and they had a big sign in The window offering new wiper and battery installation.

Mabey they they got smart.
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Old 01-11-2015, 08:54 PM
 
Location: Northeast Tennessee
7,303 posts, read 22,732,022 times
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Quote:
Originally Posted by Caligula1 View Post
Seems a very long time ago I remember someone showing me to remove one of the Battery cables while the car was running to test if the Alternator is indeed dead or the Battery..

Was I dreaming or this just a figment of my imagination..?

I need to try a home test of some sorts to figure it out..
You could try that with older cars, but I was told not to try it on newer cars with all of the electronics, etc. I had a issue with my Subaru not too long ago and just took it to Autozone and had them test the battery and alternator.
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Old 01-11-2015, 10:25 PM
 
Location: Denver
3,138 posts, read 6,901,436 times
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Quote:
Originally Posted by GTRdad View Post
I do not think that is true. If it is then it inefficient since it unnecessarily adds load to the engine. It would make more sense if the power supply to the alternator is cut off when power generation is not needed. Alternators need a source of power too to run its electromagnets
Yeah. It is true for a lot of cars.

Now newer cars like the Chevy Cruze actually realized this and it adds about 1.5% to the MPG numbers.

It has an in dash voltage meter. After you are driving for a little bit you will see it settle on 12.5 volts. Just enough to run the car and not deplete the battery. Reducing the voltage produced from the alternator reduces the load on the belt and makes for better efficiency.
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Old 01-11-2015, 10:33 PM
 
Location: NJ & NV
5,327 posts, read 12,332,087 times
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testing the alternator by disconnecting the battery while running is sort of "ghetto mechanics". In late model cars electronics rely on a stable filtered DC source and the battery is the item that filters DC. Alternators by their nature put out rippled DC because each time one coil rotates past the other you get a pulse of energy. The battery swamps this down and smooths it out.

I've always been able to tell an alternator is good by using a plain old digital voltmeter, read the voltage across the battery before you start the car, usually about 12 and change like 12.2 to 12.6 or so then when the engine is running the alternator will bring that up into the 13 to 14 volt range. Bingo, alternator is good. BTW 99% of the time alternator brushes wear out and can't contact the slip ring anymore and you get NO charging voltage or current from the alternator. brushes are small pencil eraser size spring loaded contacts. They often wear out.
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Old 01-11-2015, 10:41 PM
 
Location: Denver
3,138 posts, read 6,901,436 times
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Quote:
Originally Posted by captne76 View Post
They often wear out.
Replaced the brushes on a 2000 Audi A4 alternator and it got it charging again. $10 instead of hundreds. Win.
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Old 01-17-2015, 03:27 PM
 
1 posts, read 4,543 times
Reputation: 10
Quote:
Originally Posted by Caligula1 View Post
Seems a very long time ago I remember someone showing me to remove one of the Battery cables while the car was running to test if the Alternator is indeed dead or the Battery..

Was I dreaming or this just a figment of my imagination..?

I need to try a home test of some sorts to figure it out..
NO! NO! NO! Doing that will destroy many electronic things in your car as the voltage can approach 100's of volts with battery disconnected. In the old days, you could get away with that (pre computerized cars)
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