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Alternator overcharging  Rating:  Rating
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 Posted: 07-07-2010 04:06 am
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edward_davis
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Joined: 07-06-2005
Location: Eugene, Oregon USA
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Hello, folks!

My alternator gave up two weeks before the Healey Rendezvous. It wouldn't charge the battery, and the ignition light stayed on unless I revved above 4500 rpm. Then it would flicker, but the voltmeter stayed glued to 12. I figured it had given up the ghost.

Because I needed to be on the road soon, I purchased a rebuilt alternator from a reputable national chain. The new alternator seemed to be working OK until the second day of the meet, when the ignition light wouldn't come on, and the battery wasn't getting charged. I drove for a few minutes before I noticed the problem, so I turned around and headed home. On the way there, it picked up again, and started charging, and the ignition light would come on, properly, when I had the key on and the motor off.

But.... since then it's been charging on the high end of the range, and sometimes up in the red zone, above 15 volts. It's all over the place, too, varying between 13 and 15+ volts. The old alternator was very reliable (until it wasn't!), and always kept the needle at 14 volts, unless I ran several accessories.

Should I be concerned about charging up in the red zone? 

Thanks,

Edward

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 Posted: 07-07-2010 07:19 am
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JodyKerr
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Step 1. Get a proper volt meter on there and measure the voltage. Those smiths gauges are not always accurate. Then let us know if the alternator is doing.

Jody

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 Posted: 07-11-2010 06:15 am
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edward_davis
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OK, so the proper external voltmeter indicates a steady 15 volts at the battery while the engine is running up to 5000 rpm or so. I understood that more than 14.8 volts was bad...

The battery reads a good 12.6 volts now, so it's been charged correctly. I'm just worried that the 15 volt charging rate will kill the battery over time.

So, should I pull it out and get it replaced.... again?

Thanks,

Edward

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 Posted: 07-21-2010 10:40 pm
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Greg Fletcher
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Yes, overcharging is bad, replace before it's too late. If your battery is old it can make it burst- it happened on my car years ago and it's not pretty. I know no one wants to pay too much for parts, but you get what you pay for. Investing in a better quality rebuilt alternator can often save you money in the long run. Many rebuild alternators from chain stores are not always the best quality, many are plain junk.

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