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Old March 10th, 2010, 08:40 PM   #1
mud22
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Default Alternator/Charging problems

I just put a new alternator on my 85 chevy c30 with a 454. The alternator doesn't charge very good at an idle, about 11-12 volts, and when I turn the lights or blower motor or anything electrical on the voltage drops down to 7 or 8 volts or sometimes lower depending on what is on. When going down the road the damn thing will charge at 18 volts+ with nothing on but will still drop down when anything electrical is turned on. Does anybody know whats going on?
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Old March 10th, 2010, 10:22 PM   #2
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sounds like a possible voltage regulator problem...did you test the wiring before replacing the alternator? what was the previous one doing?
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Old March 11th, 2010, 02:09 PM   #3
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You should not have 18+ volts coming out. Is it internally regulated?
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Old March 11th, 2010, 04:17 PM   #4
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sounds like the regulator is bad.
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Old March 11th, 2010, 07:08 PM   #5
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I do believe it is internally regulated. The biggest thing I don't get is why it won't charge at an idle.
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Old March 11th, 2010, 08:58 PM   #6
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sooo....no answer on if you tested the wiring, or what the old one was doing?
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Old March 12th, 2010, 07:50 AM   #7
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Quote:
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I do believe it is internally regulated. The biggest thing I don't get is why it won't charge at an idle.
I'd be a little more concerned about putting 20 volts to my vehicle. As said above, what was the old one doing, the same thing?
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Old March 13th, 2010, 09:08 AM   #8
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No I did not test the wiring. How would I go about doing that? The old one was not doing the same thing, it just simply wouldn't charge anymore.
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Old March 13th, 2010, 11:20 AM   #9
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I would just swap the alternator again. I assume this was not new but remanned? If it is internally regulated its probably bad. Either that or you have something causing them to go bad fairly quick.
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Old March 13th, 2010, 12:22 PM   #10
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you might want to check the battery too. but it does sound like the regulator in the alt.
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Old March 14th, 2010, 12:56 AM   #11
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Quote:
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No I did not test the wiring. How would I go about doing that? The old one was not doing the same thing, it just simply wouldn't charge anymore.
here is the schematic:
http://www.chiltonlibrary.com/conten...s/85776211.pdf

first make sure the fusible link is good (which I'm sure it is), you can do that by testing for battery voltage to the terminal label "2", which should also be cast into the housing of your alternator...that wire also connects directly to the charge wire (the heavier cable on the alt.) I would do a voltage drop test on the charge wire just to verify it is in good shape.
To test the the wire at terminal "1"...first off, is the charge light in the dash coming on when you turn the key on, engine off? Does the light go off when the engine is running?
Also make sure the alternator is well grounded to the casing. It grounds through the mounting of the alternator, which grounds through the engine ground straps, so I'm betting that is OK if you arent having any other engine problems. A bad ground to the engine would also show as slow or no starter speed, eratic guages, and ignition system problems.

this will test the basics, any problems found would need further testing, but if those few tests pass, then I would replace the alternator
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Old March 14th, 2010, 11:07 AM   #12
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Thanks for the help.
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Old March 14th, 2010, 04:26 PM   #13
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How do you know the voltage output? Using the dash gauge or a meter?
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Old March 16th, 2010, 10:00 PM   #14
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Just using the dash gauge.
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Old March 16th, 2010, 10:39 PM   #15
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Quote:
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Just using the dash gauge.
get a multimeter and test it at the battery or at the charge terminal of the alternator...dash guages are unreliable and inaccurite for testing purposes
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