ALTERNATOR or Battery ?
Thread Starter
Burning Brakes
Joined: Mar 2008
Posts: 1,030
Likes: 1
From: My Give A Dams Busted The Bend Me Over State N.J
ALTERNATOR or Battery ?
Both are not much more then a year old. How do I find out which one it is this time. Ive read some other threads about what kills alternators. It sounds like im a prime candidate . I have added a battery kill switch to cut down on the run downs. But I guess I was to late. Thanks
Instructor
Joined: Apr 2009
Posts: 164
Likes: 1
From: Modesto California
First make sure the battery is charged to 12.6v. While running, the alternator should bring that up to 13.8v. If the batt. voltage stays around 12.0-12.5 than you know that the Alternator is not charging. If you do need an Alt. buy one with a lifetime warranty. Hope this helps.
Thread Starter
Burning Brakes
Joined: Mar 2008
Posts: 1,030
Likes: 1
From: My Give A Dams Busted The Bend Me Over State N.J
I cant get the gauge to read past 11.9. I was thinking it was my cluster because the temp gauge was going wackie last year. So I added a autometer gauge for that. And they share the same gauge area in the cluster . I wasnt having any dead battery issues till today, when I had all the doors open. Thats why Im trying to narrow it down. Thanks again.
Team Owner
Joined: Aug 2004
Posts: 22,303
Likes: 216
From: Sussex,Wi
2023 Corvette of the Year Finalist - Unmodified
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The best way to check it is with a Volt/Ohm/Multimeter.
Never trust the car guages completely.
That being said, what does the car gauge read with the engine running?
It should real over 12.5 volts at idle, perhaps a bit less if the lights are on. Cruising down the road, minimum of 13 volts.
If you measure at the battery with a DVM with engine running, it should read ~13 to 14 volts. (Leads on pos & neg leads of the battery).
Anything less would indicate a weak alternator.
With engine off, battery should be 11.5 volts or higher. (optimal is about 12.6v).
Alternator should always put out 13 volts or more.
Never trust the car guages completely.
That being said, what does the car gauge read with the engine running?
It should real over 12.5 volts at idle, perhaps a bit less if the lights are on. Cruising down the road, minimum of 13 volts.
If you measure at the battery with a DVM with engine running, it should read ~13 to 14 volts. (Leads on pos & neg leads of the battery).
Anything less would indicate a weak alternator.
With engine off, battery should be 11.5 volts or higher. (optimal is about 12.6v).
Alternator should always put out 13 volts or more.
Thread Starter
Burning Brakes
Joined: Mar 2008
Posts: 1,030
Likes: 1
From: My Give A Dams Busted The Bend Me Over State N.J
I found an alternator cheaper on line. I get my battery's from them.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Batteries are considered discharged at 12.0 volts or lower and fully charged at 12.9 volts or higher and linear in between. Alternators aren't meant to charge up dead batteries because dead batteries draw large charging current at first and this heats alternators and shortens their life. Always charge up a dead battery overnight with a battery charger! Dash voltmeters read low if the alternator is not charging the battery. Engine cold and running, the dash voltmeter should read 14.3 volts and it will drop to 13.3 volts engine at operating temp. Look at the dash red battery symbol light, if your alternator isn't charging the battery, it will be lit. It also lights up above 16 volts.
Car batteries self discharge up to 1% each day even disconnected. Batteries left sitting for long periods (4+wks) collect lead sulfate on their plates and become door stops. Always use a battery tender for batteries that sit for long periods. Tenders measure the battery voltage and charge them when charge falls 10% and then turn off. Batteries kept charged have a normal life, and batteries that are allowed to deep discharge have a short life. Pick one!
Car batteries self discharge up to 1% each day even disconnected. Batteries left sitting for long periods (4+wks) collect lead sulfate on their plates and become door stops. Always use a battery tender for batteries that sit for long periods. Tenders measure the battery voltage and charge them when charge falls 10% and then turn off. Batteries kept charged have a normal life, and batteries that are allowed to deep discharge have a short life. Pick one!
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