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corvette77 07-20-2011 06:40 PM

Alternator charging, then not charging
Shortly after starting the car, the alternator gauge drops to less than 12 volts and the idiot light comes on, then a minute later it's back up to almost 14 volts?
I have a new battery and I have tested both the battery (running & not running) as well as the alternator output while running. The battery tests out perfect but the alternator only shows about 13.4-13.6 volts after the motor has been running for a few minutes. Connections are tight and everything seems to work fine but the fluctuating gauge is what I can't figure out.
Thanks for any help.

EOD Guy 07-20-2011 06:45 PM

internal regulator?

LATECH 07-20-2011 06:50 PM

Worn brushes in the alternator, or intermittent regulator, more likely the first.

coupe66 07-21-2011 12:41 AM

I just bought myself a new regulator with brushes for my... eh, Volvo... And the way to see if the brushes are gone in that car is: all control-lamps in the instrument are on all the time!


willowbilly3 07-21-2011 02:41 AM

loose belt maybe?

corvette77 07-22-2011 09:05 PM

charging not charging
Belt tension is good, yes it is an internal regulator. I drove the car a bit farther distance this evening and the gauge fell to around 10volts and never came back. Just the last couple times I drove it, the gauge would fluctuate, tonight though, once it dropped down, it never came back up. I think you guys that mentioned the brushes may be correct. I'm going to take it in and have it tested and see what they tell me.
Thanks again

EOD Guy 07-23-2011 06:12 AM

I vote for a bad, or going bad, voltage reg.

timothale 07-23-2011 07:29 AM

Tractor does it
I have a bosch alternator on my Case 580, I installed new brushes,very easy, but sometimes the battery would be dead. The diesel only uses a fuel solenoid so it will run a long time on a good battery if the lights are off. Sometimes i would get a charge the sometimes nothing, I took the alt into a repair shop and sometimes it charged and sometimes it didn't during the 2 minute test. The tech said there was a loose connection inside . $ 300 for a new alt. I just carry jumper cables and can go several days with no problem. I have a GM one wire to install as soon as I get Time.

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