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Thread: Power to the trunk

  1. #1
    Constant Bitrate cazzz's Avatar
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    Power to the trunk

    I am adding a fuse block under the hood and one in the trunk.



    This marine grade fuse block has a positive and negative circuit.

    My plan is to run a battery pos and neg cable to the fuse block under the hood. This will give me 6 circuits to add accessories up front.

    The second fuse block will be placed in the trunk and power the carpc PSU, a powered sub, and future audio accessories.

    I plan on running both a positive and negative line to this fuse block from the battery.

    What is your opinion about the ground wire running to the battery vs to the chassis?

    What if I ran both a ground to the battery and a ground to the chassis near the fuse block?

    I want to eliminate the noise and ensure the ground is as good as it can get.

    Let me hear from you.

  2. #2
    Neither darque nor pervert DarquePervert's Avatar
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    Run one ground. Most say the shorter the ground, the better, which means grounding to the chassis. Make sure it's a connection directly to the chassis and the connection point is free of paint and sealer and anything else. That insures the best electrical contact.

    Also look into upgrading "the big three" to help minimize the possibility of a ground loop situation.
    Have you looked in the FAQ yet?
    How about the Wiki?



    Under normal circumstances, a signature would go here.

  3. #3
    Constant Bitrate cazzz's Avatar
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    I've read a few posts where there is noise through the audio because of a bad ground.

    I understand that the shorter the ground the better.

    But what is the real impact of running the ground back to the battery?

    What are the big three and how will those upgrades help avoid a ground loop situation?

    Thanks

  4. #4
    MySQL Error soundman98's Avatar
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    have you looked into the doing the "big 3" upgrade on your car? replacing the engine ground is part of that, as well as the battery ground.


    but quite simply, there is not one thing that anyone can say "do -this-, and you won't have noise"--if anyone tells you this, walk away--they are not very well aware of the situation or all the parts that need to work together.

    in theory, a ground wire run back to the battery can have a better connection then some spot-weld joints on the car(many new cars are built by spot-welding pieces of sheetmetal, and the electrical conductivity of the joint is directly related to the quality of the weld.). but that also suffers from voltage drop, and can lead to a heavier load on the device if not planned for carefully.

    think of it like this. when you suck water through a straw from a glass, and then blow it back into the glass through the straw-- to suck it up, you really don't need a very thick straw, but to blow it back into the glass, that same size straw becomes much more difficult-- that is what the components have to deal with. the flip side is that real copper wire is much more expensive(compared to the cheap junky copper-coated-aluminum--CCA wire), so it can be prohibitive in a lot of builds.


    is there anything wrong with connecting the chassis for ground? no, but you're relying on numerous spot weld joints to correctly carry the current without too much extra resistance. in most cases this is fine. i've put sounds systems in 4 different cars and have never had a issue using the chassis ground, or multiple chassis grounds, but that is not to say that your specific car is the same as any of the ones that i've worked on.

  5. #5
    MySQL Error soundman98's Avatar
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    i missed this, so i'll add to it..

    Quote Originally Posted by cazzz View Post
    I've read a few posts where there is noise through the audio because of a bad ground.
    yes, a lot of times, a poor ground is a installer error, by either not locating a solid grounding point, not tightening the bolt down enough, or not removing the the paint from the area for a good metal-to-metal contact.

    Quote Originally Posted by cazzz View Post
    I understand that the shorter the ground the better.

    But what is the real impact of running the ground back to the battery?
    it's all related

    think of your car body as a enormous wire. by keeping the added ground wire as short as possible, you're reducing the smaller wire's resistance to where it converts to the car's huge 'wire'.

    as i hinted at above-- the 3 major negative's of running a ground wire back to the battery are:
    1. cost-- wire isn't cheap
    2. voltage drop-- the straw analogy
    3. double the power wire to run.

    other then that, is it a bad or poor solution? no, it's not.

    but because of the added costs, i personally wouldn't do it in my own car, and is my absolute last resort to all other ground loop solutions-- which, in my limited experience, there is always another way to solve for it that is cheaper then the wire it would take to do it.

    Quote Originally Posted by cazzz View Post
    What are the big three and how will those upgrades help avoid a ground loop situation?
    this is a lengthy overview of the 'big 3'

    http://www.the12volt.com/installbay/...TID~73496~PN~1

    but as i said before, there is not a single thing that will guarantee that you will not have a ground loop. i have seen installs here and elsewhere that will take enormous amounts of time and effort to avoid having noise in the system only to have noise, where so many others just throw gear at the car, and it works fine.


    so i guess in the end the best way to avoid a ground loop is to have large quantities of dumb luck.
    Last edited by soundman98; 06-24-2012 at 03:31 PM.

  6. #6
    Constant Bitrate cazzz's Avatar
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    With all your help and input I decided to ground the fuse block to the body. There happened to be a factory grounding point right next to the fuse block mounting location.



    Checked the continuity at the neg battery terminal and it was good.

  7. #7
    Raw Wave
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    IMO there is no harm in grounding BOTH thru the body and dedicated cables. That can only minimise the path resistance and provide some redundancy (in case one fails - assuming both or all can handle the full load).


    The only qualifications are where a single ground point is required (as for certain "sensitive" audio and sensor connections), or where ground-loops in actual ground loops can occur, though that should be rare (if not impossible) for parallel grounds (as opposed to a ground going to different circuit/audio grounds.

  8. #8
    Constant Bitrate cazzz's Avatar
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    Thanks for all of the input.

    Here is my solution.


  9. #9
    MySQL Error soundman98's Avatar
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    your solution so far

    no one will really know until the gear is installed if it is a good solution.

  10. #10
    Constant Bitrate cazzz's Avatar
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    Quote Originally Posted by soundman98 View Post
    your solution so far

    no one will really know until the gear is installed if it is a good solution.
    Good point. Cross my fingers and hope for the best!

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