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Thread: Battery fusible link amperage

  1. #1
    Registered User robftw's Avatar
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    Default Battery fusible link amperage

    Whats the black fusible links amperage on the battery? I'm just going to get a car audio fuse block for this, i cant find it in the FSM or my haynes manual

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    No more body roll! SteveJ's Avatar
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    Suggestion: List your Z in your signature and/or profile.
    I'm going to assume you have a 240Z since the fusible link gauge isn't listed in the 72 or 73 FSMs to my knowledge. The fusible link for a 240Z can be purchased from MSA or Banzai Motorworks.

    Yes, I know I didn't answer your question directly. I haven't found what I consider a trustworthy conversion of fusible link gauge to ampacity. I know that Mike at Banzai is a stickler for details, so I would trust that he used the correct gauge wire for his fusible links.
    73 240Z
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    My research has lead me to believe that fusable links do not have a amperage rating per se. The guideline is to use a fusable link that is 2 wire gauges smaller that the regular wire it is in-line with. The fusable link at the starter motor must be able to carry the full output current of the alternator which is 60 amperes. Conventional fuses are not intended to carry the rated current 100 percent of the time. 80 percent is about the most they will carry indefinately. With that in mind, a 75 ampere fuse should do.

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    Registered User robftw's Avatar
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    Hey sorry, i forgot to post the car model. Its a 76 280z

    I looked over the fsm some more and the output of the alternator is 60 amps (like above) so i'm just going to put an 80amp fuse their and hope for the best.

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Default Fusible Link Amperage and Colours

    See Attachment:
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    No more body roll! SteveJ's Avatar
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    Quote Originally Posted by robftw View Post
    I looked over the fsm some more and the output of the alternator is 60 amps (like above) so i'm just going to put an 80amp fuse their and hope for the best.
    That's not a good idea. The fusible link is designed to protect the wires in the car. To select the proper ampacity fuse, you would need to consider the current carrying capacity of the wires in the circuit. The rule of thumb for 10 AWG wire is 55 Amps (NEC 90 degrees in free air. Bundling the cable drops the rating some.) An 80 Amp fuse could allow the wire to overheat. Don't forget that while your alternator may only be rated for 60 Amps, your battery can deliver a LOT more when you have a short circuit. (If you want a demonstration of that, lay a metal wrench across the battery posts and see how fast it welds to the posts. )
    73 240Z
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    You can do one of two things;
    1) replace the FL with the correct replacement part

    2) substitute with any other style fuse component and buy a good towing insurance policy, then cross yoour fingers that it dosen't leave you in a bad cell.

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    Quote Originally Posted by Blue View Post
    See Attachment:
    1976 has a Brown (Br) link that estimates out to about 30 amps, based on gauge (color and gauge shown in the FSM) and interpolated between the other "known" links. Red seems to be the popular replacement for Brown, but there appear to be two versions of the Red links, the ~30 amp, which you would get from Courtesy for example, and a 50 amp which others sell.

    There does not appear to be any supporting documentation for Brown = Red = 50 amps, but it's out there. Be careful with any fuse swaps you do.

  9. #9
    Z geek at large FastWoman's Avatar
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    Rob, I found that the main alternator-to-fusible-link wire in my '78 was pretty small -- perhaps 10ga, if I remember correctly. That's already too small to carry the sort of current that might be sent through that wire. A 10 ga wire is rated to carry 30A in household wiring, and automotive wiring seems to be twice as permissive in general. So Steve's quote of 55A for 10 ga would seem fitting. He says the rating drops a little bit in a bundle, but I think more correctly that it drops quite a lot. When you put the 10 ga wire inside an insulated wall, that's how you get a 30A rating. The alternator wire lives inside a rather large chunk of wiring harness, and it sees quite a lot of engine heat (another adverse factor). As such, I doubt it can really carry the rated 55A before melting its insulation.

    In my car, I upgraded my alternator wire to 8 ga, if I remember correctly, and then I fused it at 80A. However, if I still had the same 10 ga wire, I'd probably go with a 60A fuse and be rather uncomfortable that the wire might not be adequately protected. Of course I never like risking such things, which is why I upgraded the gauge of my wire.

    Keep in mind that if your wire gets hot enough, it will melt not only its own insulation, but also the insulation of surrounding wires. Pretty soon your wiring harness becomes toast, and you will have weird electrical problems you couldn't begin to imagine.
    Last edited by FastWoman; 05-20-2011 at 04:40 PM.
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    Nova Scotia,Canada,Earth Blue's Avatar
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    Current is charge flow per unit of time. DC or AC car or household does not matter. ... talk to Mr. Coulomb.

    The biggest factors affecting flow in wire are:

    1. Material of conductor and purity (affects unit length resistance)
    2. Effective cross sectional diameter of conductor


    I work with undersea submarine cables whose electrical loss is 0.7 ohms per kilometer.
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    The person who buys on price alone is this man's lawful prey.


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  11. #11
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    I'm not saying household AC is different from automotive DC. I'm only saying the standards are different. You won't find 10 ga wire anywhere on an automobile's 30A circuit, and you won't find a car anywhere that would meet US household wiring codes.

    .7 ohms/km?! Wow... Impressive!
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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