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Re: Battery warning light came on intermittently........ Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 14 Aug 2002 14:47:56
In Reply to: Battery warning light came on intermittently........, pursang, Wed, 14 Aug 2002 09:33:48 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The quick answer - it may or may not be trouble.
OK, electricity may be witchcraft, but that doesn't mean you can't learn a few spells.
A generator has magnets in it, and an armature that spins around. The spinning armature in the magnetic field produces electrical current. An alternator (what's in your car) has electromagnets instead of the permanent magnets of a generator. There are other differences, but this is the important one.
So those electromagnets need electrical current to work. But the alternator won't produce current until (1) it's spinning, and (2) the electromagnets are powered. Chicken and egg! Not quite- there's the battery.
The battery supplies current to the alternator's electromagnets by a wire that goes through the Battery light on the dashboard. When the current flows from the battery to the alternator's electromagnets, the light glows.
So the battery powers up the electromagnets, and once the engine is started the alternator starts spinning. This produces current, and then the alternator takes over the job of powering its own electromagnets. It's just like pulling yourself up by your own bootstraps, but with a little boost from the battery.
Once the alternator is supplying its electromagnets itself, there is no current through the battery light on the dash, and it goes out.
The voltage regulator in the alternator controls this switchover. The faster the alternator spins, the more voltage it puts out, and it's the voltage regulator's job to control (regulate) this voltage.
When you first start the car, the engine is turning at idle, about 800-1000 rpm. Under some conditions, this isn't fast enough for the alternator to produce enough voltage to take over powering its electromagnets. So the battery light glows. Once you rev the engine, the voltage climbs enough that the alternator can take over, and the light goes out.
I've seen this happen to many cars before. Just blip the throttle, and the light goes out. This is completely an alternator/voltage regulator issue, not the battery. The battery is doing its job.
If the light is on ONLY at startup, and goes out with a throttle blip, and NEVER comes on while driving after, or even idling at a light, I'd say the brushes on the alternator are getting tired or dirty. Sometimes this will act up like this for a few days, and that little bit of dirt or misconnection between the brushes and contactor in the alternator clear, and all is well. You might be fine for another year or three. If it goes away, keep an eye on it, but assume you'll need a new voltage regulator (which has the brushes built-in) at some convenient time.
But if the brushes are really tired, you'll start to see the battery light glow while idling, especially if you have a large electrical load, like the headlights, A/C blower, and your foot on the brake (BIG load from brake lights). If you drive off, the light goes out, but comes on again while idling at a light, replace the voltage regulator. The VR is easy to replace, and A LOT cheaper than an alternator. I've replaced plenty of VRs over the years in my Saabs, but only one alternator.
I hope this (long-winded explaination) helps
posted by 140.157.4...
, Thu, 15 Aug 2002 05:48:57, Wed, 14 Aug 2002 14:47:56 <-- Viewing This Message
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