Alternator Overcharging
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Alternator Overcharging
Alternator Charges between 13.9 and 14.5 volts most of the time, then it'll climb up to near 18 (!). I'm afraid to drive my vette now because I know that much of an overcharge will kill my electronics... Anyway- I've replaced the regulator in the alternator, I was told by someone who owned a vette like mine, and had similar problems that its most likely a bad connection or ground somewhere from the alternator, or even a bad battery. Can anyone point me to a wiring schematic for an alternator or battery in an '85 Vette? Or does anyone have any suggestioins of what to look for?
Advanced
Joined: Feb 2004
Posts: 51
Likes: 0
From: Mission Viejo CA
Before you do anything else, try the following: As soon as the voltage spikes HIGH, shut off the motor. Remove the alternator belt. Start the engine again; "blip" the throttle and measure the voltage with an accurate DMM. What is the voltage now? If you're around 10-11 VDC, then your regulator is defective. Order an AC Delco replacement from one of the online vendors; stay away from the Kragen/Autozone crap. If the brushes haven't been replaced in a while, they may be easily replaced as well since the alt. has to come apart again anyway....Good luck.. 
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
It was replaced with a delco... And I would try what you suggested, but the other wierd thing, if i just leave the car in the garage idling, I've never seen the voltage spike- it'll hang at 13.9 (i think its that number). The voltage spikes occur while im driving, is there any way to figure out or eliminate possibilites while driving? What are the brushes? I could try that, if those may cause an overcharge
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The voltage regulator controls the field current to maintain 14.7 volts output. If the alternator voltage goes to 18 volts even momentarily, the only thing to blame is the voltage regulator, new or not. The only other thing I can think of that would contribute would be an intermittent ground connection of the voltage regulator module in the alternator. You might check the firmness of the bolts that hold the regulator in the alternator.
Advanced
Joined: Feb 2004
Posts: 51
Likes: 0
From: Mission Viejo CA
The regulator is bad. What you have is an "out of box failure", regarding the regulator. Talk about bad luck.. The brushes, if worn, will usually cause a "no charge" condition; low voltage as the brushes lose contact with the armature shaft copper ring. Take it apart and I would do what jfb recommends: Check the tightness of the screws that hold the regulator to the alternator. Then, exchange the regulator for a new one...Sure can be a PITA when things don't work properly, isn't it???? 
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Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
I'll try one more regulator I suppose, those are cheap so its not a big deal. Anyway, Can anyone point me to where the ground for the alternator is? I wanna clean that up as well just to make sure its not a screwy ground problem. (Getting under the car is not a problem)
Pro
Joined: Aug 2004
Posts: 623
Likes: 1
Originally Posted by mikey whipreck
I'll try one more regulator I suppose, those are cheap so its not a big deal. Anyway, Can anyone point me to where the ground for the alternator is? I wanna clean that up as well just to make sure its not a screwy ground problem. (Getting under the car is not a problem)
The flexible woven strap from G104 to the frame could be the weak link.
Good Luck,
Eddie
