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Thread: Power loss when turning key from IGN to Off

  1. #1
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    Power loss when turning key from IGN to Off

    Hi,

    I installed my new CarPC yesterday and all seems to work fine besides one strange issue.

    It's a 2009 Murano, so instead of ignition key I have an ignition button. First press changes to ACC, second press changes to IGN state.
    I have a wire running directly from the battery + to the PSU (M2-ATX-HV).
    Another wire to the chassis (ground).
    Third wire is the ACC sense (split the wire going from 10Amp fuse to the stock Audio/Video control unit).

    So, when I push the IGN button once, it brings me to ACC state and after 3 seconds the computer powers up. Then I press the button again and now the car is in IGNITION state (engine is not started). Computer stays on, no problems so far.

    And now we come to the problem: When I press the button again, it switches the car to "OFF" mode and what I expect to happen is my computer to hibernate in 5 seconds because that's how the PSU (with jumpers, 5 sec delay) and Windows are configured .
    Instead, what happens is that the computer seems to continue working for about 2 seconds and then just turns off (hard off).
    It seems to me that what happens is a momentary power loss, because I hear all the fans start rotating at maximum speed when the IGN button is pressed, just like how it happens when the PC is turned on for the first time. And also the monitor displays "No Power" message, as it does when it is turned on initially.

    DMM does not show power drop, but I think it is just to slow to react properly.

    It is not clear to me what is causing the problem, 12 V wire is running directly from the battery. Also the ground wire is not switched anywhere, but runs directly to car chassis. I could understand a momentary power drop when starting the engine, but I am not trying to start the engine, just switch different ignition states with the IGN button.

    Where should I look? Any help will be much appreciated.

  2. #2
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    Have you tested the wires to make sure you have a constant 12V supply from the battery to the M2-ATX. Do you have the wires to the PC On Off switch wired correctly so the M2 can hibernate the PC prior to shutting down the power?

  3. #3
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    Quote Originally Posted by mayhem2408 View Post
    Have you tested the wires to make sure you have a constant 12V supply from the battery to the M2-ATX. Do you have the wires to the PC On Off switch wired correctly so the M2 can hibernate the PC prior to shutting down the power?
    Mayhem, thanks for replying.

    Yes, I have tested the wires. Apparently, my digital multi meter shows some change in voltage (like from 12.03 to 11.99) but I do not think it can detect a momentary power loss. I need to get an analog meter from somewhere, or maybe just a 12 v bulb so that I can see if the power is really lost.
    To you second question: I have the wires going correctly to the on/off switch on the motherboard. If I switch off the DC switch I put on the ACC sense wire, the computer hibernates as expected.

    Do you think if I put 1F capacitor it will resolve the problem? I think it will, but I really want to know what is the cause.

  4. #4
    Neither darque nor pervert DarquePervert's Avatar
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    A capacitor is merely a band-aid.

    When you measured the wires with the multimeter, did you measure the ACC line?
    With the ignition both on and off?
    This should read 0v when the ignition is off and ~12v when the ignition is on.
    Have you looked in the FAQ yet?
    How about the Wiki?



    Under normal circumstances, a signature would go here.

  5. #5
    Constant Bitrate
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    The m2 has an autolatch feature. It will keep power on for the first 60 sec. so if there is a dead spot in the acc line it should hold the supply on for 60 sec,mine also has a dead spot going from off to acc then start, i can watch mine on a DMM,im not sure how old this feature is but my M2 is a couple of years old

  6. #6
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    Quote Originally Posted by millsy View Post
    The m2 has an autolatch feature. It will keep power on for the first 60 sec. so if there is a dead spot in the acc line it should hold the supply on for 60 sec,mine also has a dead spot going from off to acc then start, i can watch mine on a DMM,im not sure how old this feature is but my M2 is a couple of years old
    That feature is still there, it does keep power for 60 seconds if ACC is disrupted.
    In my case, however, I think the problem is with the 12V from the battery. It just switches off momentarily, so ACC hold will not help. But just in case i have measured the ACC line and it behaves as expected. Also, the problem occurs when switching IGN to off, so I expect the ACC to be 0 V.

  7. #7
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    Resolved the problem.

    There is something weird with the 12V ACC going from the 10A fuse to the A/V Controller. In IGN=OFF state it short circuits to the ground. That cause the problem, the PSU was shutting itself down for protection I guess..

    Rewired the ACC to the PSU from the cigarrette lighter. No it works fine.

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