Alternator Test By Disconnection Battery After Engine Starts
09-27-2001, 08:57 AM
#1
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Thread Starter
Join Date: Dec 2000
Posts: 402
Alternator Test By Disconnection Battery After Engine Starts
I've read some posts here on the org and have been told by Autozone guys that by disconnecting the battery after the engine starts is a quick way of testing the alternator.
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
09-27-2001, 09:15 AM
#2
Senior Member
Join Date: Sep 2000
Posts: 4,601
Bad idea
Originally posted by Enduro
I've read some posts here on the org and have been told by Autozone guys that by disconnecting the battery after the engine starts is a quick way of testing the alternator.
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
I've read some posts here on the org and have been told by Autozone guys that by disconnecting the battery after the engine starts is a quick way of testing the alternator.
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
The battery serves as a voltage stabilizer, a "ballast" of a sort. If the alternator delivers charging current with an occasional "spike" (a momentary but sharp increase) the battery will absorb it. With the battery out of the cicuit, that spike will be passed along to all the delicate electronics inside the car, including the Engine Control Module. I would never do this to my car!
09-27-2001, 09:21 AM
#3
Senior Member
Join Date: Sep 2001
Posts: 242
Re: Alternator Test By Disconnection Battery After Engine Starts
Originally posted by Enduro
I've read some posts here on the org and have been told by Autozone guys that by disconnecting the battery after the engine starts is a quick way of testing the alternator.
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
I've read some posts here on the org and have been told by Autozone guys that by disconnecting the battery after the engine starts is a quick way of testing the alternator.
Well I did this by disconnecting the negative terminal to the battery while engine is running and the car kept running. One observation I made is if I immediately turn on my headlight or parking light the car will stall. But if I wait for 2-3 minutes and turn on the headlights everything is ok. Why?
Then I redo the test but this time disconnect BOTH + and - terminals to the battery and this time the car immmediately stalled.
Which of these two tests is correct? Another rep from a different Autozone told me the car cannot simply run off the alternator even after it has started since other components such as fuel pump needs electrical power. So who is right here? Thanks!
it's not a safe way to test your alternator. the voltage spike could fry your ECU or any sensitive electrical components you have.
you should goto sears, autozone, automotive store & buy a battery load tester.
first load test the battery to check that it is holding a good charge
then perform an alternator output test. there should be instruction that come with the load tester. it is an inexpensive piece of test equiment that is very useful.
and as for a car being able to run with no battery connected after it is started.......
the older cars without all the electrical doodads can run run on the alternator. but with the newer car i'm not sure, but don't wanna try could become a very expensive mistake
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