Battery Light over 2500 RPM

Jetsetter

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I recently complete a 00 PI motor swap into my 97. I developed a problem over the course of my last track day where when the motor was under heavy load the battery light would come on. This occured over the course of an hour. Now over 2500 RPM the battery light will illuminate. The engine has a brand new belt and an alternator with less than 100 miles on it. I noticed the smaller plastic clip on the alternator is broken but appears to be seated correctly. I've read that this is usually the sign of a failing alternator, but I also have a much lower RPM when this occurs than most instances.
 
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Jetsetter

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The current alternator replaced my failing one about 100 miles ago and worked until the motor swap.
 

CC'S95GT

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If the belt is tight and not slipping (you ck'd. right?)

Sounds like the rectifier has gone out in the alt. That'e what converts the a/c the alternator is puting out to d/c that the battery can use.
Take it to be tested before you have to buy a battery too.
 

Roldy

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I just went through the same thing........ I'm almost certain it's a bad alt. The way it was explained to me was over 2000 rpm's, the wire wrap starts to expand and touch the housing due to the epoxy holding it all together breaking free.......
 

ttocs

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even if it was just replaced go get it checked. Parts can be bad out of the box, hopefully you can get it replaced on warrenty then.

Although the fact that it did it after a motor swap would make me wonder if all your ground were reconnected.
 
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Jetsetter

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I also recall now that the amperage shoots upwards on the gauge rather than dropping out. Is that of any significance?
 

greenscobie86

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I bought a rebuilt alt for my Cobra for $100 from a reputable rebuilder about 4 months ago...

3 bad alternators out of the box that failed within 200 miles...

Luckily they all came with a 3 month warranty. So yep, parts like that can definitely go bad out of the box.

The upside is, I can R&R an alternator on a Cobra in about 7 minutes flat... :)
 

Roldy

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You'll boil that batt before too long and have to replace it aswell.......
I was getting 19volt spikes and nearly had the batt explode.

BAD ALT!!!!!
 

ttocs

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something is not right in your system if you have burned out 3 of them in that short of time. Are you running a huge stereo or what? I would double check to make sure you got all the engine grounds back on correctly. It sounds like it might be seeking ground through a different means then normal and burning itself out
 

greenscobie86

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^

That comment was for me I take it?

No, no big stereos here... BONE stock car... The places in Brooklyn don't like to rebuild alternators too well is all... Many have had the same luck with starters or sometimes other electrical stuff that's rebuildable..

So far the 4th alternator has been mint for the past 2k miles :)
 

ttocs

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if you had a big stereo and jammed on it I could understand, but otherwise the only thing that makes me wonder is the motor swap. Did you make any changes to the computer when you swapped the pi motor?
 
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Jetsetter

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I think you may be getting confused between him and I. The only aftermarket electronics I have on it is a temperature gauge. I'll get it tested, and I believe I have a lifetime warranty on it
 

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