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Thread: Most bizzare grounding situation...

  1. #1
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    Most bizzare grounding situation...

    Hi guys,

    I've been doing the good 'ole trace the crappy ground to eliminate line noise and alternator whine. So I stripped all the power cables and earths out to check them, at the time when it was all whining my kit was wired up like so...



    The reason they all shared the same earth and +ve was because they were within about 1 foot of the distribution block for it, so all the leads to the various equipment were very short. I ran the ground from the battery because I had bad alternator whine from the HU itself, and doing this seemed to cure it. However, with the laptop added, it was back!

    So I pulled the earths off to check where the noise was coming from. Without the laptop chassis grounded (through the parallel port on the rear) I had unbelievable line noise (mouse movement etc.). So the laptop stayed grounded, to the body, just because I ran out of slots on my dist. block. And that cut out that portion of the noise, then I only had to deal with the whine. So, after wire removal, the system looks like this...



    After adding the GLI (ground loop isolator) the noise has completely gone, but now I am very bamboozled. The HU is not earthed, I can rest it on the dash, so it isn't evening touching the mounting bracket. The wire for the earth isn't touching a thing, its just covered in tape. So I can only assume its grounding through speakers, or the RCA's to the laptop, or through the RCA's to the subwoofer, or the aerial. It isn't starved of power though, it still runs on full volume and sounds great!

    And to make things more confusing, the wire for the DC-DC invertor is plugged into an additional lighter socket I wired in. BUT the additional lighter socket isn't grounded! I took the ground off trying to eliminate the noise earlier, but all the LEDs light up and it still powers the laptop and screen fine?!?!? Even if I undo the wire that is earthing the laptop chassis, it all still works.

    Either I have defied physics here, or something very strange is going on. I can guarantee no wires are shorting to the body, and there are no additional grounds other than those specified.

    I'm not complaining, because it all works perfect, I'm just confused, because I have the ground wire for the add. lighter socket and HU just taped up and not attached to anything. I'm pretty clued up when it comes to electronics, but this really has me confused.

    '98 Peugeot 306
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  2. #2
    And then I was mod. Tidder's Avatar
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    I bet your HU is grounding thru the antenna. As far as your extra cig lighter goes, who knows. How do you have it mounted?
    Tidder

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  3. #3
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    Whoops, I should have included that in the drawing. I just took the 12v positive from the distribution block (which in turn comes straight from the battery), and soldered it into a 12v Lighter Socket. I also soldered in the ground, but as stated, I disconnected it from the distribution block where it was attached.

    As in the drawing, the lighter socket is technically in place of the Laptop DC-DC PSU, and the screen and laptop PSU are connected through to that.

    I never would have thought the antenna would be anywhere near good enough for a ground for the HU, looks like I will have to unplug all the cables one by one till it goes off. I will post back with my results.

    '98 Peugeot 306
    Project Status: I sold it ages ago!

    ShutControl

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  4. #4
    Newbie OmegaAvenger's Avatar
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    Isnt leaving everything grounded through the antenna a bad thing?

  5. #5
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    Technically, but it works doesn't it ? And I'm still not sure what it is grounding through exactly. Interesting point though, when the 3mm jack is unplugged from the laptop, the stereo makes some crazy noises - I'm thinking it might be earthing through that somehow.

    '98 Peugeot 306
    Project Status: I sold it ages ago!

    ShutControl

    The ultimate shutdown control software for laptops.

  6. #6
    Newbie OmegaAvenger's Avatar
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    Everytime I've ever left things working in a wierd way, they didn't work for very long. But as long as the electronics themselves are acting fine, id say leave it

  7. #7
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    Right, for safety's sake, I have put the wires back together properly (with proper grounds) and the laptop chassis isn't grounded anymore. I'm letting the GLI do its work, and the sound is fantastic (no reduction at all), no whine, no hiss and no crackles.

    So the HU is earthed properly, along with the aux cig lighter and amp, who knew what was going on, but I feel its better I know its got a solid earth "just in case."

    The thread really wasn't a question but more a point of interest as to how grounding can be extremely bizzarre.

    I connected my GLI the wrong way round because of the female/male connectors. Generally they are used on an output to an amplifier, rather than on an input to an AUX source. From what I understand of GLI's (someone correct me if I am wrong), they are simply 1:1 transformers, which are electrically identical, so *technically* it shouldn't matter which way round they are connected.


    Taken from http://www.bcae1.com/glisoltr.htm

    And this is how I connected mine, and how they should be used...


    '98 Peugeot 306
    Project Status: I sold it ages ago!

    ShutControl

    The ultimate shutdown control software for laptops.

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