Amazing.. Still Finding Weird Wiring Faults !

Discussion in 'Motorhome Chat' started by Jaws, Jul 10, 2015.

  1. Jaws

    Jaws Funster Life Member

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    So we have now had the Autotrail Chieftain for about 14 months..
    I thought all the weird wiring problems were done and dusted ages ago..

    Not so !

    Yesterday I decided to fit the new sound system for the TV that I bought ages ago.. Base bin and twin flat 20w speakers
    Wired it all in, mounted the speakers and turned it on.

    HUMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

    Jeez ! I had bench tested it all before the installation ( it was originally a 240v amped system and I had been 'at it' with the soldering iron and converted it to a 12v system so had to test it was all ok ) and it has worked perfectly

    After some head scratching I decided the issue had to be in the so called media centre

    Removed the whole media centre panel afair and guess what ?
    Absolutely NO negative feed on it at all.
    When it had been installed originally in the factory, someone had failed to tighten up a clamp screw on the -ve wire
    The whole system has been grabbing an earth through what ever was connected up ( as in the sat system etc ) and just earthing via the equipment chassis to each component

    Put the earth ( -ve feed ) where it should be and Lo! no more humming, no more occasional mystery interference and no more weird effects on the telly once in a while ( most of which, being a typical bodger, I had added to the 'oh well, when I get time I will sort it' factor ! )
     
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  2. Techno

    Techno Funster Life Member

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    Just in time for the news of autotrails expansion :LOL:
     
  3. DanielFord

    DanielFord Funster

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    I wonder if that is my problem? I get massive alternator whine from the radio, and the dashcam loses gps when the engine is started.
    I think I shall be ripping out the centre console again tonight :D
     
  4. Jaws

    Jaws Funster Life Member

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    That could be a duff alternator !
    You can buy a noise filter to go on the output of it though.. Just goes in line on the big thick wire coming off the alternator :)
    Usually about £12 to £15 a go...
     
  5. DanielFord

    DanielFord Funster

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    While I've got the tools out, checking the earth strap on the alternator isn't a bad idea also. :D
    I have thought about chucking in a suppressor, we'll see how it goes tonight.
     
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  6. Jaws

    Jaws Funster Life Member

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    If you do end up getting one, make sure it is 60 amp rated and an in line unit with a separate earth wire.. There are a lot out there that are little more than a choke.. while the pucka ones have an active filter in them.. And do not bother with the capacitors.. cheap as chips and for a good reason.. Never known one do sweet fanny adams !!
    Whilst a capacitor would work fine if the frequency of the noise was constant ( you could select the right capacitor and add a choke and be done ), the fact that the alternator speed changes all the time means a capacitor is as much use as a chocolate fire guard !
     
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  7. DanielFord

    DanielFord Funster

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    OK, can't find any dodgy connections, and it has now started raining, coupled with the fact we are off out in the van tomorrow. I suspect the wife will be very cross if I don't put the van back together, so I have.
    OK @Jaws since I have to rely on my schoolboy physics, and you have taken the ham exam, I need your thinking hat on :D
    I took a test at the engine battery using the multimeter, then repeated the test behind the console. I have thrown an earth strap from a convenient bodywork bolt I found, This runs the dashcam and CB. The reading here is roughly 0.5v lower than at the battery. My schoolboy knowledge reminds me that this creates a potential difference, thus the body acts as kind of an aerial. Is this correct, or have I drunk way too much gin and tonic tonight?
     
  8. Jaws

    Jaws Funster Life Member

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    You are actually spot on Daniel,
    It is sometimes very hard to get a true earth bond between everything ..
    A good check is to put one probe on a known good chassis earth point and the same in the hab area.

    Check for potential difference between them.
    That errant .5v should just as easily be lost on the +ve side as the -ve,, Doing the test as described will check the issue IS on the earthy side and not elsewhere :)
     
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  9. cruiser

    cruiser Funster Life Member

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    going to try that thanks @Jaws.
     
  10. DanielFord

    DanielFord Funster

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    Thanks @Jaws, the van has only just come back to me, and just wasted hours trying to solve a non existent problem (see my fridge thread). It is now raining, so when it dries up, I shall delve a little deeper.
     
  11. Jaws

    Jaws Funster Life Member

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    Good luck mate :)
     
  12. GWAYGWAY

    GWAYGWAY Funster

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    I think your fault might be the wiring for the entire van going through the step and the Sargent.!!!!!!!!!!!!!!!!!
    Try putting another earth on that as well it seems that the makers are not that good at wiring faults or rather they are very good at wiring faults, making them that is.
     
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  13. DanielFord

    DanielFord Funster

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    I take it that's directed my way? If so, not a bad idea. Sadly didn't get a chance to delve much today, had my niece demanding to watch despicable me, and help her do jigsaws, then she went to bed and gin happened.
    I will get under the van tomorrow, and track the fault!
     
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  14. GWAYGWAY

    GWAYGWAY Funster

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    Not really you more to JAWS as he was driven mad by a wiring fault. so it was a snide comment
    Bad earths are the major electrical fault always check them first, look at the number of flashing rear indicators with rear/ brake lights going off and on same with trailers when everything flashes. Tighten all the chassis earth tags with a spanner and check for corrosion.
    Best of luck cos electrickery is the worst fault to find.
     
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