Help please charging system!!!!

Discussion in '6.9L IH & 7.3L IDI Diesels' started by SDbernhardt, Jan 11, 2018 at 10:10 AM.

  1. 79jasper

    79jasper Chickenhawk

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    Probably somewhere between the obs coming out, and 94.
    Because far as I knew, they (obs) all had it.
    Many say the bulb acts as a fuse. But on the other hand, that's supposedly what the resistor is for.
    Is ifrythings still a member here? I was just reading some of his post on this exact thing on another forum.

    Sent from my SM-G892A using Tapatalk
     
  2. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    How many oil burners does it take to......

    LOL
     
  3. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    Looks like it, @ifrythings logged in earlier today.....
     
  4. DrCharles

    DrCharles Registered User

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    The bulb does not act as a fuse, nor does the resistor. In the event of an internal regulator short, the bulb will limit the current, but it doesn't blow. The resistor only carries a fraction of the current mostly passing through the bulb, and as already said, is there to still "tickle" the regulator into exciting the alt even if the bulb is burnt out.

    "Make everything as simple as possible, but not simpler". (common paraphrase from an Albert Einstein quote) :D
     
  5. ifrythings

    ifrythings Full Access Member

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    The bulb is not a fuse, it's a current limiter so you don't blow out the lamp driver circuit.

    In the red box in the photo below is a typical lamp driver circuit use by ford, as you can see when the ignition switch is on, current flows through the bulb (and resistor) into the "I" terminal of the regulator, then through R7 (10 ohm resistor) and into the transistor. Now if you put 12v directly to the "I" terminal the only thing limiting current to the transistor is the 10 ohm R7 resistor which will let 1.2 amps of current through, the transistor is rated at max 1/2 amp, guess what releases the magical smoke?

    Depending on how the regulator was design this failure may cause the light to be on or off forever and the alt charges the system or no charging with or with out the light being on.

    CS3341-circuits.jpg

    I have seen poor connections between the bulb socket and instrument cluster which would cause problems with the earlier design of the resistor being part of the bulb socket which is probably why ford moved it to the back of the cluster circuit board.

    Also the exciter circuit must be switched with the ignition, if tide to a constant power, the regulator will keep the field coil in the alternator on (~3-5 amp draw) and kill your batteries.
     
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  6. franklin2

    franklin2 Full Access Member

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    I don't know if you can eliminate the bulb circuit on the internally regulated alternators or not, but on the external type(the type shown in the above picture) Ford elimnated the bulb by putting direct ignition 12v on the "S" terminal of the regulator, no "S" connection to the alternator, and eliminatng the "I" connection all together, it just sits there with no connection at all.

    But of course most guys are not messing with this old external reg stuff, they are messing around with the newer internally regulated 3g stuff.
     
  7. 79jasper

    79jasper Chickenhawk

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    Good info there.
    I was going off the slightly newer trucks (psd) So I guess not quite the same. Lol

    Sent from my SM-G892A using Tapatalk
     
  8. laserjock

    laserjock Rebuilding! Supporting Member

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    When I did my new harness I did away with all that. My excited for my 3g Alt is off the key on circuit for all my other key on circuits under the hood.

    So that is an option if your dash has gone south on you. You’ve got a bolt gauge stating you in the face. It’s not hard to know if it’s charging or not.
     
  9. Macrobb

    Macrobb Full Access Member

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    I think that while it's only rated at 1/2 amp continuous, it'll handle the 1.2+ amps for a short period of time(until it overheats), because I've directly connected it on a test bench, and it got hot quickly... but still worked afterwards when I connected it correctly.

    You still need the limiting bulb/resistor.
     

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