Loud Alternator Hum
Thread Starter
4th Gear
Joined: Aug 2004
Posts: 4
Likes: 0
From: Mpls MN
Loud Alternator Hum
Hi All,
I have an 89 stock Vette. It is my first one and I've had it for 1 year now. I bought a scantool recently and after I finished seeing how it worked the Batt. light was on. I started it up and it was not charging. I had to be somewhere fast so I went to NAPA got one and threw it in. It worked fine. The next day I noticed a loud hum with the key on and the engine off. I was making sure it was the alt. with a screwdriver. The screwdriver stuck to the front cooling fins on the alt. Is there anything I should check or should I just return the alt?
Could the scantool in any way have caused this. It is an Actron 9150. I used it in the field service mode to clear some SRS codes.
Thank you
I have an 89 stock Vette. It is my first one and I've had it for 1 year now. I bought a scantool recently and after I finished seeing how it worked the Batt. light was on. I started it up and it was not charging. I had to be somewhere fast so I went to NAPA got one and threw it in. It worked fine. The next day I noticed a loud hum with the key on and the engine off. I was making sure it was the alt. with a screwdriver. The screwdriver stuck to the front cooling fins on the alt. Is there anything I should check or should I just return the alt?
Could the scantool in any way have caused this. It is an Actron 9150. I used it in the field service mode to clear some SRS codes.
Thank you
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
With the ignition on and the engine not running, any buzzing noise you hear from the alternator is likely the field coil being energized. Modern alternators have a pulse width modulated field current and since the alternator isn't turning, the voltage regulator is driving the field with the maximum width pulses in an attempt to get 14.7 volts output. Of course there is no output because the alternator is not turning. I doubt there is anything wrong with your alternator.
Instructor
Joined: Dec 2004
Posts: 176
Likes: 0
From: Oakland CA
Originally Posted by tjb
Thanks for your reply.
What you say makes sense, but would'nt all alternators hum?
What you say makes sense, but would'nt all alternators hum?
Thread Starter
4th Gear
Joined: Aug 2004
Posts: 4
Likes: 0
From: Mpls MN
Originally Posted by RatC4
Exactly. Maybe shorted diodes or a bad regulator. A D.C generator has a cutout relay to brevent reverse current flow when it isn't making power, the diodes in the rectifier serve the same purpose. Silicon can go bad open or shorted. Sounds like yours shorted.
I will return this Alt. and get a new one first thing in the morning. I will put it in right away and let you know what happens. Thanks again for the help.
Instructor
Joined: Aug 2004
Posts: 179
Likes: 0
From: Florida
Originally Posted by RatC4
Exactly. Maybe shorted diodes or a bad regulator. A D.C generator has a cutout relay to brevent reverse current flow when it isn't making power, the diodes in the rectifier serve the same purpose. Silicon can go bad open or shorted. Sounds like yours shorted.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I've been to NAPA twice in the same day to exchange one of their humming alternators. The hum was the bearing and had nothing to do with the alternator output. If it's singing, I'd take it back and get another one.
One of the Corvette Mags did an article on alternator rebuilds years ago - the only one they found with completely new internals was the A/C Delco. All of the others were fortunate to have new paint on the case.
One of the Corvette Mags did an article on alternator rebuilds years ago - the only one they found with completely new internals was the A/C Delco. All of the others were fortunate to have new paint on the case.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Originally Posted by tjb
Thanks for your reply.
What you say makes sense, but would'nt all alternators hum?
What you say makes sense, but would'nt all alternators hum?
The other posters don't comprehend well, tjb hears his alternator humming when the engine is NOT running and the ignition is on. His alternator has no symptoms of a shorted diode or any other defect.
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Thread Starter
4th Gear
Joined: Aug 2004
Posts: 4
Likes: 0
From: Mpls MN
Originally Posted by jfb
Modern alternators can hum, it depends on how well the iron laminations in the field are varnished together.
The other posters don't comprehend well, tjb hears his alternator humming when the engine is NOT running and the ignition is on. His alternator has no symptoms of a shorted diode or any other defect.
The other posters don't comprehend well, tjb hears his alternator humming when the engine is NOT running and the ignition is on. His alternator has no symptoms of a shorted diode or any other defect.
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