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Thread: Alternator Question

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    Super Moderator JohnRogers's Avatar
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    Alternator Question

    Alternator Question: During my Vintage Air install it was determined my alternator was bad. I asked for the most powerful alternator available, yeah channeling my inner Tim “Toolman” Taylor. So, I believe a 100amp alternator was installed. The voltage regulator and ballast resistor were also swapped out. I love the bright lights and quick power windows. The gauge seems to show almost constant charging while I’m driving. My radio keeps shutting down and my power sunroof won’t work, both are fine when the car isn’t running.

    Do I have to swap out alternator for something closer to 60amps? Is there something else I’m not considering? Did I mention how much I like the bright lights and quick windows?

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    Aspen and Volare Super Member 77rr2x4s's Avatar
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    Back then most cars were 41 to 65 amp alt. So the wiring might not be up to the task of a 100 amp. Most of the 100 amp mopars back in the day had heavier wiring for the alt and engine compartment. You may have overheated some of the wires on the harness somewhere. Possibly ground issue also or bad regulator. Check you output at the battery while running. IIRC above around 14.5V is usually too much.
    Last edited by 77rr2x4s; 10-29-2018 at 08:50 AM.

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    Aspen and Volare Super Moderator aspen79's Avatar
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    Something is not quite right. The alternator shouldn't be charging the battery constantly, no matter what the amperage, provided the battery is good. The alternator is technically a battery maintainer, not charger. The car runs off the battery and the alternator works to keep the battery fully charged. If it needs to charge 100% of the time, the life will be shortened. Not saying this is what's wrong with your car though. Biggest destroyer of alternators is a weak battery. I've seen it 1,000 times at work. A weak battery won't cause over voltage though. The regulator will limit max voltage regardless of the battery.

    Check voltage at the battery with the engine running. At idle with a good battery, you should see roughly 12.8V to 13.5V. At higher rpm it should never rise above 14.7V (vehicles built in the last few years excepted from that). It doesn't matter if the alternator is putting out 20 amps or 200 amps, providing the load is less than that, lights and accessories will work the same no matter what.

    What I'm getting at is, you could run a 200 amp alternator (no reason to but you could) with no problem, provided the voltage is regulated correctly. Make sure you regulator has a good ground, and all your connections are clean and secure. Test, or get tested, the battery. I don't mean an electronic test with a handheld device but an actual load test with a carbon pile equipped tester. Those can also do charging (and starting) system tests as well.

    One other thing about the high amp alternator and 77 is correct, the wire to the alternator stud will not carry a full 100 amps and really needs to be upgraded to a larger one. The majority of the time, the alternator won't be putting out anywhere near 100 amps but if the battery gets run down, it could for a short while.

    Hope this helps or gives you a place to start checking.
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    Aspen and Volare Super Member 77rr2x4s's Avatar
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    Did you ever get it fixed?

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    Super Moderator JohnRogers's Avatar
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    Quote Originally Posted by 77rr2x4s View Post
    Did you ever get it fixed?
    I wound up putting in a factory rated alternator and was reminded those guys at Chrysler knew better than I did.

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    Aspen and Volare Administrator White Aspen R/T's Avatar
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    I got a nice new 60 amp one from Spider Marine.
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