Alternator and Battery Problem
Thread Starter
Instructor
Joined: Jun 2010
Posts: 111
Likes: 2
From: Warren Ohio
Alternator and Battery Problem
Took my '79 out yesterday afternoon for an hour long trip. Noticed that according to my gauge, there was barely 12 volts charging. On the way home in the dark with my lights on, the gauge then showed less than 10 volts. I keep the battery on a float charger and the battery is only about
2 years old. The float charger light shows red after an overnight charge.
It normally turns green after a few minutes of being connected. Has anyone had a similar problem? Is it a faulty battery, alternator, or some other weird Corvette only issue?
2 years old. The float charger light shows red after an overnight charge.
It normally turns green after a few minutes of being connected. Has anyone had a similar problem? Is it a faulty battery, alternator, or some other weird Corvette only issue?
Melting Slicks
Joined: May 2011
Posts: 2,753
Likes: 119
From: Springfield Missouri
have the alternator checked out, sounds like the internal regulator is going bad. You rebuild it yourself or buy a replacement, if you have the original, have it repaired to keep the original parts on the car.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 111
Likes: 2
From: Warren Ohio
Engine isn't original, so no problem putting in a rebuilt alternator if that's the issue. Someone told me that the negative ground on the frame could be the problem. I removed and cleaned it using battery terminal "grease" but everything looked clean. Battery terminals are also clean and tight. Don't know what else to look at.
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
I agree with the alternator/regulator being the most likely problem...but as already said, have the battery load tested after being charged. Occasionally a battery can have an internal short and show the same symptoms of a bad alternator.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
measure the voltage when cranking, better not fall below 10.5 volts, or battery is bad/discharged.....which could still be a alternator problem....
get the car started....alt out stud should read 14.8 on initial startup...if not, it could be bad....13.3 + to 13.8 is a good running average after a while.....
this is why the typical AMP METER is useless in a car....and even GM went to voltmeters later on ......
Drifting
Joined: Aug 2005
Posts: 1,443
Likes: 65
From: Wauconda IL
GM went to voltmeters from a cost perspective. Less/cheaper parts involved and most folks don't know the difference anyway.
A voltmeter only shows voltage but an ammeter shows the current draw in either direction- This is more indicative of what is going on with your charging system.
A voltmeter will only indicate something can't maintain the voltage. You still don't know if it's the alternator or battery that is at fault.
With an ammeter, if you are always registering positive, yet the battery won't stay charged, you most likely have a battery problem whereas if it's reading mostly negative, you most likely have alternator issues (assuming all your connections are otherwise clean and tight).
Just my .02
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Race Director
Joined: Sep 2005
Posts: 18,640
Likes: 121
From: Farragut,TN
I have to politely disagree-
GM went to voltmeters from a cost perspective. Less/cheaper parts involved and most folks don't know the difference anyway.
A voltmeter only shows voltage but an ammeter shows the current draw in either direction- This is more indicative of what is going on with your charging system.
A voltmeter will only indicate something can't maintain the voltage. You still don't know if it's the alternator or battery that is at fault.
With an ammeter, if you are always registering positive, yet the battery won't stay charged, you most likely have a battery problem whereas if it's reading mostly negative, you most likely have alternator issues (assuming all your connections are otherwise clean and tight).
Just my .02
GM went to voltmeters from a cost perspective. Less/cheaper parts involved and most folks don't know the difference anyway.
A voltmeter only shows voltage but an ammeter shows the current draw in either direction- This is more indicative of what is going on with your charging system.
A voltmeter will only indicate something can't maintain the voltage. You still don't know if it's the alternator or battery that is at fault.
With an ammeter, if you are always registering positive, yet the battery won't stay charged, you most likely have a battery problem whereas if it's reading mostly negative, you most likely have alternator issues (assuming all your connections are otherwise clean and tight).
Just my .02
Thread Starter
Instructor
Joined: Jun 2010
Posts: 111
Likes: 2
From: Warren Ohio
Thanks to all of you for your help. I tested the battery and alternator as suggested by "ezbens" using a Fluke tester and found that the problem was the alternator not charging.
It was below 13 volts on start up. Will replace it tomorrow.
It was below 13 volts on start up. Will replace it tomorrow.
Drifting
Joined: Aug 2005
Posts: 1,443
Likes: 65
From: Wauconda IL
mrvette provided the troubleshooting details for you.
Just to confirm, did you check the voltage at start-up on fast idle?
If you only checked at idle speed (750 RPM or so), you might not get an accurate picture. If the voltage is low and stays low even when revving the engine, then I would suspect the alternator.
Melting Slicks
Joined: Oct 2002
Posts: 2,865
Likes: 1
From: I may be getting old but I refuse to grow up
I'd rebuild it but that's me. Had it down to 45 mins to take it off the car rebuild and get it back on the car. I would also take it and get it tested before getting a new one