Alternator Wiring Question
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Alternator Wiring Question

  1. #1
    Senior Member W.O.T's Avatar
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    Default Alternator Wiring Question

    Finished up wiring the motor on my boat except for two wires. Where do the Red and White wires off the alternator pigtail connect to?

    Alternator is a standard GM automotive deal.

    Thanks

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    Not sure on your plug's color code, the post with the nut goes to the battery, the terminal furthest away from that previously mentioned post goes to the post (battery), the only remaining terminal goes to a battery idiot light if desired otherwise it goes nowhere.

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    If one wire has a significantly higher end-to-end resistance reading (it should, Ni-chrome resistance wire), it belongs on terminal 1.
    This is the "field" terminal, and gets a reduced voltage signal, which forces the alt. to charge. This one is switched from the ignition.
    15 ohm resistance, or 4 feet of 1027 Ni-Chrome wire @ 3.75 ohm/foot.
    1029 wire @ 9.4 ohm/foot needs 1 foot 7 inches.

    Terminal 2 is for 12vdc feed from the + bat. post or starter solenoid battery post. Stator terminal.

    The above is for a Delco 12-SI, internally regulated, your results may vary.
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    As has been said, only one of the 2 terminals on the pigtail is needed since the 2nd terminal runs the "idiot light" in cars that are equipped with one. A little more detailed explanation as to what it does...this terminal feeds the charge voltage to the regulator, which turns the regulator on to power, or "excite", the field coil in the alternator.

    The field coil is the "spinning magnet" inside the stator that induces current into the stator as it spins. Instead of an actual magnet, the field coil becomes the magnet when it's powered. The regulator increases or decreases this field coil voltage to vary the intensity of the magnetism given off by the field coil. By varying the magnetic intensity of the field coil, this is how the regulator to control how much current is induced into the stator, which therefore controls the available charge voltage on the charge post. The "excite" wire as it's commonly called, is the wire that tells the regulator how much voltage is available at the charge post so that the regulator knows whether to increase or decrease the field coil voltage to maintain a constant voltage at the charge post regardless of the load placed on the alternator up to the amount of current the alternator is rated to be able to supply to the load. No voltage on this terminal = no field coil voltage, and therefore no magnetism in the field coil to induce current into the stator, thus the alternator won't charge.

    If I remember right, I believe it's the terminal farthest away from the "charge" terminal that is the "excite" wire. In common practice, this wire is usually connected to the "IGN" (i.e. ignition) terminal on the key switch so that the regulator turns on and off with the key. However some have had great success by just connecting it straight to the charge post, in effect making it a "one wire" alternator.
    Last edited by Jetaholic; 01-18-2009 at 08:59 PM.



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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    According to what I found last night, the "excite" or "Field" terminal (#1) is the closer one to the output.
    The alternator housing has numbers cast into the metal anyhow.

    A jumper could be run from The output to the #2 terminal (since both are bat-live), but not to #1 (unless it is resistance-wired).

    Showing "low" voltage to the "F" terminal on the regulator is what triggers charging.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by SmokinLowriderSS View Post
    According to what I found last night, the "excite" or "Field" terminal (#1) is the closer one to the output.
    The alternator housing has numbers cast into the metal anyhow.

    A jumper could be run from The output to the #2 terminal (since both are bat-live), but not to #1 (unless it is resistance-wired).

    Showing "low" voltage to the "F" terminal on the regulator is what triggers charging.
    Thanks for the correction Aaron. I understand the "low" voltage present signal and how it triggers charging. Of course, this low voltage is created by the voltage dropping due to how much of a draw you have on the system. The larger the draw, the more voltage applied to the field coil, which increases magnetic field intensity of the field coil and thereby induces more current into the stator to increase the voltage drop across the stator, which is the voltage available at the charge terminal.



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    Quote Originally Posted by W.O.T View Post
    Finished up wiring the motor on my boat except for two wires. Where do the Red and White wires off the alternator pigtail connect to?

    Alternator is a standard GM automotive deal.

    Thanks


    So you got that baby wired yet? Give me a call or PM. We'll grab some beers.




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    Sweet Thanks For The Pic And Replies!

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    I wired mine from the spade to the post. I've heard this will drain a battery with the key off wired this way. I've got a master cut off switch, so I don't know if it will. It's been working fine this way for years.

    Tim

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    Quote Originally Posted by River Rat 005 View Post
    I wired mine from the spade to the post. I've heard this will drain a battery with the key off wired this way. I've got a master cut off switch, so I don't know if it will. It's been working fine this way for years.

    Tim
    It won't kill the battery.

    It would however kill the battery if the idiot light wire was hooked up and the other "side" of the light hooked up to ground (should be on ignition)

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