Cable to Alternator Overheating

Discussion in 'Marine Electrical / Electronics' started by ArchHibb, Oct 23, 2019.

  1. captjohn

    captjohn Captain

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    My experience with wires that are carrying too much current is that they tend to show evidence of heating along most of, if not all of, the wire run. This is not the case with this cable.

    The fact that the damage is localized suggest something else is going on. Do you still have the old cable? If you do, I would carefully slice the insulation open along the length of the wire with the tip of a knife from the insulation on the lug to past the damaged wire insulation, and peel it off carefully, to see what happened. Look for evidence of arching to ground, broken strands or a loose crimp. It may be difficult to see anything, severe overheating has a tendency to destroy all the evidence in the process.

    My gut feeling is your dealing with a vibration problem, all the flexing of the cable is occurring right near the lug.
     
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  2. ArchHibb

    ArchHibb Captain

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    Thanks to everyone for the replies and ideas. To answer a few of your questions:

    The alternator is Cat's standard 50 amp.
    The cable was a brand new Ancor 2 AWG tinned copper.
    The cable does not/cannot contact the engine mount.
    The belt dust is due to a slight mis-alignment between the alternator and the engine which will be fixed this Winter.
    I second the theory that over current would distort the cable along its entire length.
    The old cable deteriorated exactly like this one; damage to the jacket/insulation exposed the copper core which then began deteriorating in the marine air environment.
    I have looked for and been unable to find any evidence of arcing.

    This red cable connects to a smaller black wire inside the alternator via an external lug.
    The internal black wire shows zero signs of thermal distress.
    The lug was cleaned to bare metal before the new cable was installed.
    A (plastic?) ring insulates the lug from the alternator case, but it fits only loosely allowing the lug/cable to swivel/wobble relative to the alternator. However, no contact between the cable and the alternator is possible.

    I may have the alternator tested if for no other reason than to eliminate it from the equation.
    Captjohn's gut feeling about vibration being the problem sounds plausible. Unless a definitive answer shows itself, I plan to replace the cable with a longer one that creates a larger sweep (curve) and further from the lug.
     
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  3. djmarchand

    djmarchand Captain

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    How about feeling the new lug for heat with some DC load on the alternator? With the kind of melting/charring you are seeing, it should burn your hand. Confirm that before doing anything else.

    David
     
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  4. leaky

    leaky Captain

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    I have seen auto alternators w/ a fusable link inline, protection on the alternator is not that crazy of an idea but why you are seeing the problem is another question.

    To me it looks like a faulty cable, resistance created right at the crimp somehow, got bent around a lot so you are putting everything through less of the strands.

    Or maybe the insulation is getting cracked or worn away and it's causing an arc to ground.

    The cable is right next to an engine mount. My guess is when the boat is running that cable is getting vibrated back & forth repeatedly - maybe the engine mount(s) is/are going bad and that's what changed?

    Having the alternator tested isn't a bad idea, I would do it given this is the 2nd time it's happened, but I think you have a mechanical problem going on.. If the alternator comes back OK, and you see nothing wrong engine mount wise, I would replace it with a perfectly made marine cable of sufficient size, making sure not to over-stress it during installation, and try running the cable inside of a stiff piece of hose to provide chafe protection and support. Run the boat a bit and keep an eye on it.

    Also make sure all the connections, grounds included (ie make sure alternator is well grounded to block, clean surfaces if that's how it grounds) are all good in the process of course.

    Jon
     
  5. leaky

    leaky Captain

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    The other thing I might ask is how was the cable made, ie are you crimping it yourself and how are you doing it if so, or how did the crimp look on it originally? They sell hydraulic crimpers on Ebay for about $40/shipped that do a superb job of making a 360 degree crimp on any cable size they can handle, I believe 2 gauge is no issue but I remember I could not use them on 4/0 so the sizes of jaws provided do not go all the way to the largest cables.
     
  6. crabz

    crabz Senior Member

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    Just thinking out loud here, a few things:

    I don't understand that connection? How does that not go to ground?

    A red cable that hooks to a black cable after the connection? That seems kind of odd to me.

    Is it wired correctly? What is the function of the red cable?

    This all worked fine for many years until recently ?

    When DC does weird things it's usually the ground.
     
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  7. Old Mud

    Old Mud Captain

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    Arch, did you ever solve your problem?
     
  8. ArchHibb

    ArchHibb Captain

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    Not yet. Alternator is coming out this weekend once the engine is winterized. After that has been checked, I’ll be checking for any overdraw, then replacing the cable. Will report back!
     
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