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> Lights dim as rpm goes up?
koozy
post Sep 25 2007, 01:39 AM
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What the heck? I never drove my car at night until tonight. I get in and start the car. Drive down the street and notice the lights are kind of dim but not too bad. I step on the clutch and when the rpms go down to idle the lights get brighter. So I pull over and check it out. The lights dim as I increase rpm and when I let go of the gas and come to idle.... 3 seconds or so after it's at idle they get brighter. I've seen the opposite happen but never this. What could be happening?
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Spoke
post Sep 25 2007, 03:03 PM
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I had this same thing happen on my 74 Dodge Colt. Lights dimming at night, battery discharging. Let it idle and the alternator slightly charges the battery. Rev the engine and it discharges. WTF?

I took the alternator apart, put an ohmmeter on the armature through the brushes. Had low resistance not spinning. Spin with my hand and the impedance went up. Not good. The current through the armature sets up a magnetic field that gets picked up by the stator (stationary windings around the armature) which produces the voltage.

My fix since I was in college and poor, was to remove the brushes, clean them and clean the contact area on the armature since it was very dirty from about 8 years of use. Brushes were worn but not shot.

Put it back together and into the car. At this point my battery was just about dead so all parking had to be done on a hill to clutch bump start it. Bump started it and at idle I had more than 15amp charging. Rev'ed the engine and charging went above 30amp.

Unless you feel like ripping your alternator apart, go get a new one.

Spoke
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