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Thread: high amp alternator on 1998 disco

  1. #1

    Default high amp alternator on 1998 disco

    Hello all! I have installed a high amp alternator in my '98 disco and have somewhat come to a tree in my my under bonnet fuse box has two hot leads coming into it: one directly from the stock alternator and one from the batery positive! These feeds come in on opposite sides of the fuse box. The fuse box circuit is actually split into two and if the 100 amp alternator fuse blows then part of these circuits remain powered by the battery(necessary for safe driving) and, providing your alternator is still working, it powers the rest of the circuits!...correct me if I'm wrong pls! I am of course having to increase the wire size from my new alternator to the battery and that 100 amp fuse is incompetent to protect my new alternator and would not allow the extra amperage available from the new alternator to supply the load from aftermarket accessories I intend to install! Not to mention there is no reasonable way to get the size wire I am using with connectors inside that fuse box! Now to my question! I want to run my hot directly from my alternator to the battery and then run a wire or two if necessary to the stock fuse box! I thought about just keeping the stock wire from the battery to the fuse box, leaving the 100A alternator fuse and running my positive lead from alternator to battery with separate protection in the line! If I do this however that entire fuse box will be running off the battery if the alternator were to fail and I dont want this as it would drain the battery much too fast and im sure thats why the factory split the fuse box in the first place! At least thats the best explanation I have been able to come up with! Wut I dont understand is that if the stock alternator failed and the 100 amp fuse didnt blow then all these circuits would be powered by the battery anyways (which happened to me) so why was it split in the first place? Also is it really necessary to keep the box split or can I just bridge the 100A fuse, run the stock wire from the battery back to the fuse box and a stand alone wire coming from the alternator to the battery positive with protection in between? My alternator is a 225A mean green replacement for this vehicle and I am going to install a 200A circuit breaker in between the new alternator and battery! I am currently running one optima yellow top and soon to add another battery bank and isolation system! Then I will be ready to move on to major electronic! Any advice is appreciated! Slanders are illl advised!

  2. #2
    Join Date
    Sep 2007
    Philadelphia, PA

    Default Charging Systems

    The 100A fuse on the old set up is to protect the wiring, not the alternator.

    You can keep the current LR set up using your new parts in this fashion:
    Being that you have upgraded from 100A to 225A, as you stated, you will need to upgrade the wire from the new alternator to handle the amps. Downloadable charts are found all over the internet too calculate amperage * distance = cable gauge
    Subsequently, you will need to upgrade the fuse.
    Finally, you can purchase proper ring terminals to handle the larger gauge wire whilst still being able to fit the alternator to the fuse block with a smaller ring.

    I've completed a similar setup using terminals purchased from NAPA. I prefer using marine Bussmann manual reset w/test breakers within the engine bay. These are waterproof and very rugged. Google: Series 18X Hi-Amp Circuit Breaker

    You had made a suggestion regarding connecting the alternator directly to the battery... This is the way it was performed prior to the advent of engine bay fuse blocks. There is no harm. Be sure to add the inline fuse/circuit breaker between the alternator and the battery as to protect the wire.

    Lastly, you stated that you planned to use a dual-battery set-up with isolation. You will be able to save many headaches by going with a marine battery isolator and gauging the wire accordingly from that point, i.e. 200A to isolator with two, 1 ea., 100A supply lines to original LR set-up. Remember, the installation of fuses/circuit breakers, when dealing with high amperage, is usually within 6-12 in. of the supply side.

    Good luck,
    Last edited by joshua.mcguoirk; 10-19-2014 at 06:12 AM. Reason: Errata
    1990 RRC, 3.9L, AUTO "Willow Pond" (Sold)
    1996 D1, 4.0L, AUTO "Lucas"
    1999 RR, 4.0L, AUTO "Belle" (Sold)

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