How to tell if it's the alternator or battery..? (vehicles, auto, idle)
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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..
if you have a voltage test meter, start by measuring the voltage at the battery, it should be about 12.5 volts. next start the engine and let it idle, set the meter up to measure the voltage again, it may still be 12.5v, at this point rev the engine up to about 2000-2500 rpm and recheck the voltage, it should now be between 13.5-15 volts. if not then the alternator is dead or dying, if so then the battery isnt holding a charge. this test will tell you which component to take to the parts store to put on their load tester.
If memory serves me, start the car, turn the headlights on, then take the positive cable off the battery. If the headlights dim, possible the alternator is bad.This isn't foolproof, but it may be what you were remembering. rbohm has the correct way to check. The other way is po'boying it, and may become very costly in the end.
Let the engine run for a couple of hours with the headlights on. Shut it off and see if it restarts with pretty good juice and if the lights remain bright. If the battery is still strong, its the battery, which will take a charge, but won't hold it. If it grows weak, it's the alternator,, which is failing to charge the battery.
If you don't already have a battery tester (you obviously don't), they cost about 50 bucks and you will use it only once in your life. Maybe twice. An auto part store will test it for free.
Read this first, then drive to an auto parts store and look over their shoulder while they test it.
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..
Go to an auto parts store and have them test your battery. They all do it, and they all do it for free.
Simple. Get a voltmeter and put the red lead on the hot cable on your alternator. Ground the black lead to the engine block. You should get around 14 volts with the engine running. If not then your alternator is bad. Pull the battery and have it load tested at an auto store.
Once the alternator goes bad, the car runs off the battery until it goes dead.
With my car, the voltage difference between a good, OK, and a bad battery is very small. Its within 1 volt Im pretty sure.
Also on most modern cars, when the alternator goes bad, your battery light on the dash should turn on right away. That will start your countdown and you have minutes.
If the battery was completely drained, like no lights and absolutely no power, time for new battery.
Seven posts and no one mentioned a bad voltage regulator. Everything runs off the battery. When the voltage in the battery drops below 12.v, the votage reg opens and lets current flow to the battery. When the engine is running, the alternator is always producing current. On newer vehicles, the volt reg is a PCB in the alternator and goes bad far more often than the alternator. If the dashboard red 'bat' light is not on while the engine is running, it's not the volt reg or the alternator. And if you read any auto maintenance book, subject relating to 'electric', it advises to NEVER run engine with cables disconnected from the battery. Not good for the alternator.
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..
Don't do this with any car less than about 40 years old. This is a good "hillbilly" test for a car with a GENERATOR, but not with an ALTERNATOR.
As others have posted, probably going to any chain auto parts store for a free battery test is your simplest way to test the battery.
If you are willing to break down and buy a simple test meter, even a cheaper one, simple enough to test battery voltage - rough cut, if the battery voltage is higher with the car running than with the engine off, the alternator is working, at least nominally. If the running voltage is lower, the system is not charging.
Another simple tool you can use is a small "floating ball type" test syringe to measure (roughly) battery electrolyte density. You need to rinse this dude out with distilled water after use. If you have an "open" battery, one you can add water to, you can test density in all 6 cells, if most of the balls float and you get the same reading in all cells, your battery is basically OK.
Before condeming the battery, check water level in the cells (distilled only, and use eye protection while working around batteries) and add if necessary, and if the battery terminal connections are dirty/corroded, clean them up. You can get a device to put in your cigarette lighter plug that uses a 9V battery to keep radio codes, etc, from going away when you unplug the battery.
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