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Thread: PC Causing Noise, Suggestions?

  1. #11
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    Make sure to upgrade the ground straps from the engine to the body however.

    And if you have any other heavy battery cables going to the body of the car make sure those are up sized as well. As I mentioned elsewhere most cars normally have a ground strap that almost looks like bolted wire mesh that goes between the engine block and the body of the car.

    My old cop car had two ground straps from the engine to the frame and had 4 separate ground straps from the frame to the body of the car. 2 of them were from the exhaust pipe to the body of the car. These were all factory installed.

    Do not rely on the body mounts to pass the ground signal from the engine to the body of the car especially since in most cases the engine mounts are rubber or plastic bushings.

    You want to use the same type of cable that the factory uses. So if you are replacing the battery cables themselves they are generally quite small from the factory. I think it is common for instance for GM to use 6 gauge wire. In any vehicle I am not running power cables directly to the battery I would always up size the cables to the car its self. So you would want to go to a 4 or 2 gauge wire in those cases depending on the size of your install. The ground strap can be a little harder to find but it is designed to handle high temps, oil and gas spillage. It is simply a copper mesh with connectors on both ends. You can add more of them to add more capacity or get bigger ones.

    If you know of a good grounding point on the frame you could also run a standard cable from the battery directly to the body of the car away from the engine.

  2. #12
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    Quote Originally Posted by mrwesth View Post
    Well put!

    Taking my own thread slightly off topic:
    Fortunately I have had a number of tech jobs in different fields where a large part of the job was troubleshooting... both new installs and old shoddy work. Needless to say I jumped ship and am in grad school now as the money wasn't worth the hassle. However, I did get a lot of satisfaction from finding the solutions to problems others couldn't.
    That goes right in line with why I enjoy tinkering with projects like this and the challenge to overcome each hurdle. I think that 90% of my interest in going the car pc route was for the fun of the install (and subsequent tinkering to get it just to my liking).
    I'm sure the same holds true for many others that take on these projects.
    i was the same way.. i really enjoyed trouble shooting low voltage stuff at my last job-- i was the best tech they had(many places requested me to service any of their issues instead of just letting the company send out a random tech)... but the money just wasn't there..

    Quote Originally Posted by mrwesth View Post
    Back on topic:
    I just need a free weekend (ie not pending midterms or research papers to write) and a case of beer and I have no doubt I can take care of the noise issue.
    However, in the meantime is there a good read on learning more about ground loops? I have at best a rudimentary understanding. Are there any good diagrams of ground loops in a car application? Google searches show some home theater setups and it seems the ground loops there are always caused by two connected devices. Would that be the amp and the carpc--and the loop is through the rca connection? Or could a loop be caused by multiple grounding points from engine block - body - frame?
    I would love to understand what causes the problem rather then simply troubleshooting until it goes away. 'Cause learning is fun, yo.
    simply put, a ground loop is a difference in voltage potential to ground.

    think of the carpc and the amp as 2 glasses of water, and think of the rca cable as a tube running between the glasses. if you take water out of the 'carpc' glass, water is going to rush in from the 'amp' glass to replace it until the water level in each glass is exactly even. and if you were to remove some water from the 'amp' glass, water will again rush in from the 'carpc' glass until everything is even.

    that is essentially what is happening with a ground loop, except that one glass is constantly trying to be emptied, and the tube is constantly trying to make up for it.

    usually a ground loop is caused by different resistances-- either because one device is using a longer wire to reach a shared ground point, or the ground point connection of a device has a higher resistance then another interconnected devices separate ground point..

    the idea that needs to be accomplished is to get both devices evenly matched, so voltage isn't flowing between them-- that voltage is what is causing the whining.

    and that is about as far as you should need to know for the methodology to fixing it ground loops are insane little gremlins that pop up whenever they feel like it.. you could just throw a sound system in 'just for a weekend' and won't have a single problem with it no matter how hacked, or i've seen it plenty of times where someone will spend hundreds more then they need to, to make every effort to avoid a ground loop situation, only to end up getting a ground loop..

  3. #13
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    So I had a free hour today (had to deal with laptop hdd crash last weekend :shakefist: ) and here is what I tried and found:

    • Ran 8awg from psu to battery negative -- caused little to no change, perhaps slight noise increase.
    • Ran 16 from rca ground to psu ground post -- caused the noise to increase.
    • disconnected psu ground and connected phone mp3 player to rca -- noise eliminated.


    Does this mean the PSU is the source of the noise? I do have a 400w inverter and 250w desktop psu I could try.

    I believe there are 2 distinct noises:
    (1) a low volume but high pitched whine when I rev up , I assume this is the alternator and
    (2) a static like ringing that cycles on and off lasting 3-5 seconds and going off for a second, I am guessing this is caused by the PSU?
    The whine is not so noticeable, the ringing is very irritating and only drowned out completely at 50-75% plus volume or driving 60 on the interstate.

    My other thoughts for the source of the problem:
    • Something with my two battery setup. The factory amp is connected to battery 1 while the psu/subs are connected to battery 2. But I would think that wouldn't matter with 0/2 connecting the two positive battery posts directly, right?
    • I guess my last thought goes back to a ground loop. I like the 2 glass analogy and that begs the question here about something I may have neglected to mention: the wiring harness.
      I know this wiring harness is grounded to a small gauge wire that was for the stock radio. It is perhaps smaller then my rca's ground as I am running 16awg per channel and have a total of 4 channels running to the wiring harness. That means a total of 16awg x 4 grounds running from the harness to the pc.
      Maybe I should try splicing the wiring harness ground to an 8-10awg and ground each of the rca's at the wiring harness side to the same ground point?


    Thoughts?
    Last edited by mrwesth; 02-02-2013 at 03:32 PM.

  4. #14
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    Solved!
    Finally got around to re-grounding the wiring harness. Ran it to the psu and both sources of noise go away. Appears it was a ground loop after all.

    Thanks for help and suggestions!

  5. #15
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    great to hear you got it all worked out!

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