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Old 16-09-2009, 17:16   #1
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Alternator Issues

Okay, I took my alternator to a shop to have it tested. They told me it was working great.

I installed it back on my engine and it looks like it is only putting out 1 volt give or a take a bit. Now this may be a rookie question, but could this be that the 1 volt is because the battery is pretty much fully charged? Or should the alternator put out 14ish volts no matter what the state of the battery?
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Old 16-09-2009, 17:29   #2
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How are you checking

How are you checking the 1 volt? where are you putting the meter leads?
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Old 16-09-2009, 17:34   #3
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The Ground on the meter I tried on the block, and on the neg post, and the 1 volt was coming off the alternator output #1 on the picture.
I guess I should have tried the positive on the battery as well while it was charging maybe I would have got my 14+ volts there?





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Old 16-09-2009, 17:37   #4
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regulator

I'll assume your alternator is internally regulated.....Is your tachometer working?
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Old 16-09-2009, 17:38   #5
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actually, you should be seeing battery voltage at the alternator if nothing else.
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Old 16-09-2009, 17:52   #6
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Quote:
Originally Posted by Sailmonkey View Post
actually, you should be seeing battery voltage at the alternator if nothing else.
Hmm, thats right actually. I never thought of that. I will have to do some more trouble shooting tomorrow.
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Old 16-09-2009, 18:01   #7
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Here's an odd question: Are you sure the meter is OK? If you connect it to the battery, with the car off, are you seeing "12" volts?

if the meter is good (on the right scale, etc.) and the alternator bench tests as good, then the alternator 'excitor' isn't exciting the alternator. That is, the alternator is not getting power (from your battery via the ignition key) to excite itself, and without that little tickle it can't put out power from the main output.

Your picture looks like a typical Delco...in which case, #4 is a test point, and #2 and #3 are the critical wires going out to your harness and key. Those circuits need to be completed properly, or you'll get no output, regardless of how fast the alternator is spun.
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Old 16-09-2009, 18:11   #8
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I double checked the meter with my spare analog one. It is working fine. I will just have to do some messing around I guess. I will figure it out, I just thought maybe i was missing something really obvious.

From the website i took the picture:



  1. This is the main power wire that goes directly to the battery. Make sure it is a heavy gauge since it has to carry the full output of the alternator (up to 100 amps).
  2. This is the field wire that energizes the alternator. It must be switched, or else it will drain the battery overnight. Do not wire this into the coil power wire that you use to switch the engine on and off (a seemingly elegant solution), since once the engine is running the alternator will feed power back through this wire, which will then power the coil, and you won't be able to shut your car off.
  3. This is the lead for the sensing wire that goes to the idiot light in your instrument panel. A neat tip: if you aren't using a voltmeter or oil pressure gauge, run this wire to a light mounted somewhere on your dash. Since you usually can't hear if your own engine is running in the derby, when this light lights up you know that your engine has just quit (or the alternator has just stopped charging).
  4. This is the regulator bypass hole. Sticking a long thin metal object about 2 inches deep into this D-shaped hole causes the alternator to go to full charge. If you do this while it's dark out and the main power wire is disconnected, the whole alternator will emit a cool X-Files type glow. I don't recommend that you try this since you'll likely end up toasting your alternator.
Thanks for all the help so far. I appreciate a second or third brain when I am stumped a bit.
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Old 16-09-2009, 18:25   #9
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Is the hot post of the alternator connected to the battery? It sounds to me like the battery switch might be off.
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Old 16-09-2009, 18:35   #10
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One other thing to check: is the alternator field/sensing connectors clean and free of corrosion?

Steve
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Old 16-09-2009, 19:14   #11
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I'll just chime in with a suggestion to check your grounds. You probably did already, but ground leads are much more likely to corrode than positives, & they can cause all kinds of weird things.
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