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alternator voltage

Discussion in 'The Garage' started by cegusman, Jul 20, 2006.

  1. cegusman

    cegusman 3/4 ton status

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    What should the voltage be when the alternator is charging?
     
  2. u2slow

    u2slow 1/2 ton status

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    It needs to be higher than the battery.

    13-14V is fairly normal when running. You should have 12-13V at the battery when shut down.

    I always check with a multimeter if I suspect anything because the stock gauges are kind of flakey.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Alternator is always charging, just varing amounts.

    At the alternator, typically you will see 13-14.5 volts, but you really want to measure that with all your accessories on, to make sure that during high demand, the battery is still being maintained.
     
  4. RustyParts

    RustyParts 1/2 ton status

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    Voltage at battery terminals should be between 13.8 and 14.2, but usually anthing above 13 is good.
     
  5. cegusman

    cegusman 3/4 ton status

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    Thanks, thats what I thought. Mine is reading around 12.1 volts. Time for a new one I guess.
     
  6. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    It all depends on what voltage your battery is.
    Fully charged, it should be close to 14.5v
    An alternator only puts out amps @ whatever voltage your battery is at, regulated to 14.5v max. If your battery is sitting at 10v, and you start your truck, your not going to see 14.5v right away, it will take time for the battery to charge up to 14.5v. It will jump up to 10.5 or so right away, and will slowly rise from there.
    If you run your truck and turn everything and you see your voltage start to drop, you know your then exceeding the amperage your alternator is putting out. It should never drop suddenly, it should slowly drop .1v at a time.

    Certain vehicles under certain situations are designed to run that way, cost for the OEM's is too high to put 200amp alternator in every car. For instance, in your brand new escalade, if you start it on a cold day, turn on your heated front and rear seats, heated cup holders, full blast blower, wipers front and rear, lights, radio, nav system, make a call on your on-star, all the while the battery has been discharged to 11v to start the thing on a cold day so the it's being charged as well, and your sitting idle in your driveway, so the alternator is not putting out much. The vehicle is running in negative mode, voltage will slowly drop. But they know everything won't be on all the time, you'll turn down or off the heated seats & cup holders, drop the blower motor, turn off the rear wiper, and end your call on on-star, and start to drive bringing up the RPM's and thus the amp output on the alternator, swinging it over to positive charging.

    If you disconnect your alternator wiring (removing all loads), and then measure the voltage at the alternator, it should be 14.5v or so.
     
  7. cegusman

    cegusman 3/4 ton status

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    I tested mine with 2 fully charge yellow top optima and the 6.2 running with no accesories on and it only read 12.1 volts. Had the truck running for a good hour and the voltage never went up.
     
    Last edited: Jul 20, 2006
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Unclear in your responses, but were you measuring at the alternator? Depending on wiring and location, you can/will get different voltage.

    12.1 while running is low though, no matter where you measure.

    You can rebuild the alternator for about $20, if it interests you to see the insides of one. One of the easier things to "rebuild" on the trucks.
     
  9. roadnotca

    roadnotca 3/4 ton status

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    X2. Should be 14.2 at the alternator.
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    test it first...

    I'd do a quick check to ensure 12V is present at all 3 terminals on the alternator with the engine running (the "stud" terminal the big red wire attaches to,and both the red, and white or brown wires on the 2 prong plug)..if the white or brown wire is getting no juice,the alternator wont energize and charge...and neither will a new one!..:crazy:
     
  11. goldwing2000

    goldwing2000 Guest

  12. cegusman

    cegusman 3/4 ton status

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    System is wired correctly. Got the alt tested yesterday and it was bad. Waiting on my upgraded 94amp one to show up today.
     

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