Dc p/s

Discussion in 'General Electronics Chat' started by Blueberry, Mar 23, 2014.

  1. Blueberry

    Thread Starter New Member

    Mar 20, 2014
    2
    0
    Hello members ~

    I have a 12-Volt dc CCTV security system that was installed professionally a few years ago. It was working fine until recently. It is an 8 camera set-up.

    The monitor's picture screen went black with the words "No Video" displayed across each of the 8 video channels.

    I have no idea of how or when it happened.

    Thinking that the problem would be resolved if I rebooted the DVR and powered off & on the power supply panel that energizes each of the cameras, I tried it; I waited about a 1/2 hour or so before turning on the power supply and booting-up the DVR.

    On initial start-up, I would get a crystal clear video picture on all 8 cameras. I tried this several times. The first time, within several minutes, the video picture would become wavy (like ocean waves) then the image would fade and turn snowy; and then completely black- with the words, "No Video" across each of the channel's screen.

    With subsequent attempts of turning off and on the DC power supply, the same thing would happen but at different time intervals- from, within a minute to as long as 15 minutes or three or four hours later.

    I replaced the DC power supply distribution panel- same problem.

    I also replaced the DVR- same problem.

    The cable/wire used for each camera is: CM75C RG59U 1x20 AWG 95 with 2C/18PWR CCTV cable. [If I had to describe it, the exterior jacket is similar to Romex- where a single sheath encases the coax cable and the two separate 18awg stranded coated wires; as oppose to Siamese cabling.]

    I disconnected all the BNC connecters from the DVR; Using a Fluke model 117 dmm, I checked each one of them for continuity and for stray voltage; I have continuity (tone) and there are no voltage readings at either the center pin of the BNC connecter or at the BNC's outer metal jacket.

    The DC input voltage at the block leading to the distribution bar (strip) is 13.52 Vdc.

    The DC input voltage at each of the circuit/connection points (without any camera connected to them) are #1: 13.54 Vdc, #2: 13.55 Vdc, #3: 13.35 Vdc, #4:13.55 Vdc, #5: 14.49 Vdc, #6: 13.52 Vdc, #7: 13.47 Vdc, #8: 13.36 Vdc

    With the camera's wires attached to the connectors on the power strip, the voltages drop to 8.88 Vdc, 8.59 Vdc, 8.86 Vdc, 9.0 Vdc, 8.71 Vdc, 8.81 Vdc, 8.8 Vdc, 8.96 Vdc; respectively

    Incidentally, even with all the cameras powered up, the DC input voltage at the block leading to the distribution bar (strip) remains at 13.52 Vdc.

    Using alligator clips to keep the test leads of my voltmeter attached to the connection points on the distribution bar (strip), I removed the camera's power lead wires (one-at-a-time) and saw an immediate increase in voltage- back to their initial 13.XX Vdc readings.

    1.) I don't understand why the voltage changes/power losses are occurring;
    2.) Are there are any other troubleshooting tests or testers I can use to pinpoint where the problem lies?

    I just find it incredulous that all 8 cameras are affected at the same time.

    Any help or suggestions would be deeply appreciated.

    Kindest Regard ~
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    Sounds like you have a power loss problem along the distribution cables.
    Disconnect all but one camera and see if the problem goes away.
    I suspect you have a bad connection somewhere between the distribution bar and the camera cables.
     
  3. Blueberry

    Thread Starter New Member

    Mar 20, 2014
    2
    0
    Thank-you; I'll give it a try- and I'll keep you posted.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    sounds like your supply has failed with time. probably filoter caps have dried out.
     
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