Lights dim at high revs
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I noticed this earlier but dismissed it. Then again yesterday, it happened again. I was out enjoying a little drive and noticed that when the revs go over about 4500, the lights (interior and exterior) dim by something like 50%. When the revs go back below 4500, they come back up to full power. It's a stock car and I've had not other troubles. What do I check?
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I'm with Kelly on the voltage regulator.
Take a simple voltmeter and measure the voltage at the battery when you are revving the engine.
With a healthy regulator you should see about 13.0V - 14.4V. Anything higher or lower indicates a charging system issue.
Battery voltage lower than 13V is usually an alternator charging issue. Higher than 14.4V is typically a regulator.
As an example, I have seen an '87 Carrera output 30V with a failed voltage regulator. Weird things would happen such as the radio turning off at higher RPMs, etc.
HTH,
Scott
Take a simple voltmeter and measure the voltage at the battery when you are revving the engine.
With a healthy regulator you should see about 13.0V - 14.4V. Anything higher or lower indicates a charging system issue.
Battery voltage lower than 13V is usually an alternator charging issue. Higher than 14.4V is typically a regulator.
As an example, I have seen an '87 Carrera output 30V with a failed voltage regulator. Weird things would happen such as the radio turning off at higher RPMs, etc.
HTH,
Scott
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Thanks for the suggestions. I think I have a voltmeter, or I'll borrow one, and check it out. I did change the belts this fall and will double check them too.
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Originally Posted by jnnking
Thanks for the suggestions. I think I have a voltmeter, or I'll borrow one, and check it out. I did change the belts this fall and will double check them too.
JRG
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Jr and Seege,
How does a slipping belt cause this? Not questioning, just trying to learn. I would assume it would cause a drop in the recharging ability of the alternator, but that the battery would have enough stored up to cover the short fall.
How does a slipping belt cause this? Not questioning, just trying to learn. I would assume it would cause a drop in the recharging ability of the alternator, but that the battery would have enough stored up to cover the short fall.
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I'm no mechanic and the voltmeter to the battery sounds like a better suggestion than mine. But dimming lights at higher revs was a symptom of a slipping alternator belt back in the days when most of us could work on our own cars, the dimming was usually accompanied by a squeel.
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Originally Posted by jnnking
I noticed this earlier but dismissed it. Then again yesterday, it happened again. I was out enjoying a little drive and noticed that when the revs go over about 4500, the lights (interior and exterior) dim by something like 50%. When the revs go back below 4500, they come back up to full power. It's a stock car and I've had not other troubles. What do I check?
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Originally Posted by jnnking
Jr and Seege,
How does a slipping belt cause this? Not questioning, just trying to learn. I would assume it would cause a drop in the recharging ability of the alternator, but that the battery would have enough stored up to cover the short fall.
How does a slipping belt cause this? Not questioning, just trying to learn. I would assume it would cause a drop in the recharging ability of the alternator, but that the battery would have enough stored up to cover the short fall.
Simple to check, if there's more than an inch of play in the belt is need to be tightened. You could then charge the battery by simply driving on the freeway for 15 minutes....
JRG
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Dumb follow-up question. Is the alternator behind the cooling fan? I thought i knew where it was, but I was thinking of the AC compressor.
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Here's the new info and my new question. I took the battery to an auto store, they tell me it's good. They test the electrical system with the car running and say it's 90% likely to be the alternator but need it off the car to check. I checked the voltage across the battery. It's 12 v when off, 11.7v at idle and 11.6 when reved to 4000 rpm. Is the voltage regulator separate from the alternator? Do I need to replace my alternator?
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Alternator or Regulator sounds like it's toast. It should be pumping out around 13.6 to 14 volts. I am not 100% on this, but, I believe the regulator is internal to the alternator on these vehicles.