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Power line split

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  • Power line split

    I'm runnung a 4 or 6 G wire to my computer. I may put an amp in my trunk later that will ONLY feed a 10" sub (it's not an amp to shake the neighborhood, just to give me maybe 5db more base). There shouldn't be any problem w/ me splitting that line to feed both right? I would put a fuse by the battery and also a fuse before the amp and computer.

    Also, is it OK to ground back to the negative battery terminal or should I ground to the body? What are the pros/cons/pitfalls of the grounding choice?

  • #2
    4AWG or 6AWG would be way more than enough for a car PC. 4AWG is a safer bet if going for a car PC + an amplifier.

    As for the grounding choice, the pros of connection directly to the battery terminal are virtually none. You should however attempt to ground all audio components to the same point in order to avoid a ground loop. This includes the head unit and/or amplifiers for the speakers. Ground runs should also be kept as short as possible. You can likely get away with grounding everything separately to the chassis of the car but make sure you have good contact to bare metal at your grounding points.
    "You're just about as useless as JPEGs to Helen Keller" - Wierd Al


    • #3
      Originally posted by blafrisch View Post
      Ground runs should also be kept as short as possible.
      With that alone I'm embarassed because I know this since I deal with this daily; with what I do I can't ground longer than 3'. So I should know that a run back to the battery from the trunk is out of the question regardless. Just wasn't thinking. Thanks.


      • #4
        ^that's not completely correct.

        if your going to use longer then average(about 1-3' long ground wires), it is heavily recommended to step up a gauge of wire to account for voltage drop.

        think of playing with a straw in a glass of water-- if you suck teh water in(the amp receiving power off the positive wire), the straw can be kinda small without really affecting how fast you can suck the water in.

        but the straws diameter quickly comes into play when you try to push the water back into the cup(the amps negative wire). stepping up the diameter of the straw you use makes it easier, and the amp feels the same way.

        by using the same sized wire for power and ground, and keeping the ground wire short, your relying on the cars chassis--which, for the sake of argument, is like a enormous wire -- by doing that, your minimizing how hard the amp needs to push the power back out..

        but here's the catch-- with todays cars with all the spot welds joining a lot of thins sheets of metal, there are some times where a body panel might not make a solid electrical connection to other panels, creating a 'tight' pathway for electrical power.. in this instance, it is better to run a wire back to the battery to get around this, and provide a better electrical connection for the amp.

        is either incorrect? no. they both have their applications. running a ground wire to the battery will be more expensive(both in wire cost, and installation time), and that typically makes it less desirable, but the actual connection method is not any less desirable then using a short cable to the car chassis.

        personally, i won't consider running a ground wire back to the battery unless there are some serious issues with grounding to the chassis, like the aformentioned poor spot welds.
        My OLD 2001 Mitsubishi Eclipse GT:
        "The Project That Never Ended, until it did"

        next project? subaru brz
        carpc undecided


        • #5
          I wouldn't quite go with that straw analogy... (After all, the pressure in both directions is equal, and the current is cyclic - ie, goes from the battery +ve thru its -ve though GND to the load and out its +ve back to the battery +ve... oops - you use conventional current don't you...? [See caveat below.])

          But the bottom line is the same... It is usual to have a better/heavier GND than what exists on the +ve side.
          Some of the reasons include:
          - it's usually cheaper - ie, the chassis etc can be included;
          - the last thing you want to lose is GND - that is often catastrophic for equipment (assuming other GND paths exist, and invariably they do).

          [ Ok, so alternate paths suggests a lesser GND is required. But that creates ground loops (of the dc kind), and you shouldn't rely on signal etc cables completing the power-GND requirements. ]

          I happen to run +12V & 0V (GND) from the battery for my HU, and my spare batteries.
          For the HU it's IMO simpler - I guarantee a simple & clean GND path.
          For the other batteries, ditto - it overcomes bad GNDs thru bolted or rubber insulated ute trays.

          In both cases, I see no reason not to also add a parallel cable-chassis-cable GND path.
          Or rather - paraphrased - if I relied on a chassis GND path, I see no reason not to add a dedicated GND wire (back to the battery).
          In fact, many vehicle manufacturers do add the seemingly redundant GND wires rather than rely on former traditional practice of simply using metal-to-metal GNDs (eg, taillight assemblies, pressed bulb cradles, etc).
          It's usually a case of cost or weight versus reliability or need.

          Of course, not that a good HO amplifier's performance should vary as a result of voltage drops in its supply... (Nope - I add no caveat for that one!)
          But if I had a seemingly typical high output amp, despite a solid & heavy chassis GND path (to lessen cable costs), I might also run a full-path GND cable if only to reduce total GND resistance.

          Caveat - wrt "conventional" and electronic current and all that bullsh - I'm merely pointing out that +ve and -ve, or "supply" and "return" makes no difference. The electricity is the same on either path. If not, charge would lag or build up in some part of the circuit, and that couldn't continue (even if that were to occur). Water can be pooled, electricity cannot.