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(Post Link) post #1 of 4 Old 09-02-06 Thread Starter
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Quick electrical question

When at idle, my headlamps go quite dim. But if i give it some revs they brighten up somewhat. Is this normal? Is it a sign of alternator/ battery problems?

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Re: Quick electrical question

Alternator may be struggling or perhaps battery is on it's last legs. Any half decent garage/mechanic that you trust can check battery for health.

Most cars headlights are a little dimmer at idle though so unless pretty bad I wouldnt worry
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Re: Quick electrical question

Some slight dimming is normal but anything more than that could point to the fact the battery needs replacing.

An alternator charges the battery at 14v to 14.75v at anything above 1,000 revs. The higher the voltage the brighter the head-lights will look. At idle the alternator will still be charging the battery slightly but not sufficient to power a lot of the electrical devices as well.

At idle, a battery produces about 12.5v with no electrical load on it (anything drawing a significant current). Under high load conditions, plus during any very cold weather, this can drop to 10.5v to 11v. The amount the voltage can drop by depends on the condition of the battery (basically how old it is) and if it was under-specified (capacity in ampere-hours) in the first place. It's quite possible for the voltage to drop to only 9v under these conditions.

If your battery is more than 3 to 4 years old I would get it checked and think about getting it replaced.

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(Post Link) post #4 of 4 Old 10-02-06 Thread Starter
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Re: Quick electrical question

Thanks for the response, i'll get the battery checked over.


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