Alternators
Car Batteries

How can I test my alternator to see if it is discharging my battery?

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2010-03-29 11:40:08
2010-03-29 11:40:08

You can have the alternator tested free of charge at just about any major auto parts store. By the way, a bad alternator will not "discharge" a battery - the alternator's function is to provide the charge to the battery. If the alternator is faulty, then it is not providing the charge necessary to keep other components from discharging the battery.

I had the alternator tested and it was charging. If the alternator has a bad diode, it will discharge the battery. I replaced the alternator and everything is fine.

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Related Questions


I pulled the negative cable from the battery with the truck running and the engine quit. Is this a test to see if the alternator needs to be replaced?

Your 12 volt battery should be about 12.5 volts without the engine running. Test and verify it is. Now with the engine running test again, Voltage should now be around 13 to 14 volts. If not, then your battery or alternator are bad. To check a battery try charging it with a battery charger.

Here is a test u can do to see if Ur alternator is good or not . when car is running disconnect the negative battery terminal it's the black wire.If car stalls then the alternator is bad if it doesn't stall then it's Ur battery is bad and u have to replace it

The gauge inside is telling you how many volts your alternator is putting out, not yoru battery. Go have your alternator tested to see if it is putting out 14 volts or more...........if not, you are drawing more current out of the battery then what the alternator is replacing and you are going to end up with another dead battery. They can test alternators at Autozone for free or you can go get a multi meter and test it yourself. Have the alternator checked.

to see how strong your battery is

The battery light is letting you know that the alternator is not charging the battery. Check to see if alternator is any good. Also check to see if belt is hooked up.

Assuming the new battery is good! The usual problem why a battery is not charging is the alternator. The battery will be discharged if the alternator is not working properly when you start the engine and when the engine is running, etc. The vehicle uses the batteries electricity instead of the alternators electrical output, and of course if the battery is not being replenished by the alternator the battery will fail in a short period of time. You should test the alternator to see if it is putting out between 12 and 15 volts. Another possible things that could be the problem with a New battery failing so quick is, maybe the proper amount of acid was not put into the battery, a short in the wiring, etc.

First, get a volt meter. Test the voltage of the battery before starting the car, then start it and see if the voltage increased. You should see a jump of about 3-4 volts. Alternatively, if the car has a manual transmission, you could tow the car in gear (very slowly, about ten MPH in first) with the engine off and the battery removed and test to see if the alternator is generating power. Without the battery it should only make about one or two volts, but you will be able to notice it on a voltmeter.

Why do you want to unhook your battery??? If the alternator is good the car will continue to run, if it dies then you have a bad alternator this is why you would want to unhook the battery cable to check and see if you have a bad alternator

Yes- a load test can check to see if the battery has failed, or is just discharged. Soemtimes the battery is still good, but the charging system (alternator, drive belts, cables, voltage regulator) may be bad. Most shops, and many auto parts stores have a load test meter and will check the battery free for you.

Either check your alternator or your battery life and replace as see fit.

you need to do a voltage test and see if there's a greater load of energy returnig to the battery and compare it to the load leaving. if your return is greater then the problem most likely will be your battery.if there is no or low voltage returning from the alternator check your wiring and or consider another alternator change. another test. turn on your car , while the engine is runing disconect your battery positive first then negative. this test while not accurate it will most likely tell you if the alternator is working.(the car should stay on)

The ABS light is likely coming on because the voltage being put out by your battery isn't enough to satisfy the requirements of the ABS system. It could be either the battery or the alternator. Put a load test on the battery and make sure that's operating within the requirements, and put a volt meter on the battery after starting the car to see the alternator recharging the battery. I've seen it both ways, alternator is bad and need a new one, or the battery is bad and need a new one.

Either the battery is bad and won't accept a charge or the alternator is not putting a charge into the battery. Have the battery tested. You can hook up an inexpensive volt meter to the battery while the car is running. You should see from 13.5 to 14.5 volts if the alternator is working properly. If it is less than 13.5 volts then the alternator is not charging.

the same way you test any alternator. use a volt meter and put one lead on the positive and one on the negative of the battery and see if the volts are more than 13volts. if it is above 13 it is charging

Is the battery being charged by the alternator? You should see 13 volts or higher while the engine is running, otherwise you will need to test the alternator. another answer: the alarm system. get it disconnected by a mechanic--mine was constantly draining the battery on my 95 pathfinder.

take it to autozone and they will check it for free.

CAUTION!!! This may be a problem with the alternator and the charging. Blower fan will stop working if alternator is not charging. You may also see the battery light and brake light staying on as well! Advance Auto Parts or Auto-zone can test your alternator/battery.

It's a complicated answer, as there is no real set in stone replacement interval. You can easily TEST your alternator whenever you want, using a simple $2 voltmeter. The volt reading on your car battery should go up by about 1-2 volts from when the car is not running, to when it is idling, this is one sign that the alternator is working and charging the battery.For much more details, see the related link. This link also describes a different way to test your alternator.For what its worth, I have a 2000 echo with over 170,000 miles on it, and the original alternator is still working fine. I've also only had to replace the car battery one time.

Check all of your connections from the alternator, see if the are loose or corroded. Make sure battery cables are not loose or corroded. Check the battery ground wire connection to the body of the car also. If everything appears OK you will need to test the alternator output or have it tested. You may need to replace the alternator or voltage regulaor.

power is too low, probably a bad alternatorAnswerit could be the alt but it might also be your battery this just happend to me i had to change me battery terminals cuz they were lose it u can move ur terminals then u need to change them cuz that meant that ur battery isn't charing and its working off the alternator now if you wanna see if your alternator is bad turn your car on and while its on open the hood and take out either the positive or negative terminal of the battery only one and if the car turns off then it means your alternator is bad u will need a new one if it stays on its ur battery take ur batter to auto zone and they will test it for u to see if its charged enough or if its no good

Not a good sign, This could mean that your charging system (alternator) isn't doing its job. If you have problems starting the car due to not enough battery power, then check your battery to see if it is holding the charge. If after a while that you had to boost or jumpstart your battery your car gradually dies then check your alternator to see if it is putting out charge to the battery.

Check to see if the alternator is working Connect a voltmeter to battery: Without engine running reading should be about 12.8 With engine running reading should be 13.8-14.2 If not bad alternator


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