djolejr

Hi. I have installed CCTV system that is consist of: 6 cameras, 1 DVR Dahua 3108E, 3 power supplies, UTP 24 AWG, video baluns. Main problem is there are hum bars only over two cameras during low light conditions. These two cameras are on the same power supply 2A, 12VDC. Others cameras have separate supplies . During daytime picture quality is good, but during low light conditions, there is this problem. I have tried to change power supply and video baluns, but that did not solve problem. I have measured DC current between video balun GND and DVR GND, and there is 6,7 mAmps of DC current during daytime. I can not measure during night because i can not access this place. Schematic diagram is placed here as attachment. Also, this is recorded video: http://img809.imageshack.us/img809/4003/egpeeoxjsrbkfvrrvajsdy.mp4. (http://imageshack.us/clip/my-videos/809/egpeeoxjsrbkfvrrvajsdy.mp4/) It is noticeable that when one camera turn off or dimm IR LED, hum bars are reduced. I assume that there is some problem with internal camera power supply that produce some hum or some kind of Ground loop. System is not grounded. Cameras are mounted at brick wall, outside building. UTP cables are all new, and placed through pvc cable canals mounted at walls inside building. Thanks for suggestions. Ivan.

Sorry, but i do not understand You. Can You explain me more detail. Thanks. for baluns to work they need to be direct DVR to camera. (un balanced) as soon as you split cat5 then baluns cant do there job. you would be better cat5 to power supply like your picture then from power supply rg59 to cameras your picture is showing DVR blue/ blue w and orange / orange w for video yet at camera orange for both video too many joins for baluns to work as they should There are not RG59 cables, only Cat5e. All cables are Cat5e 24AWG. This picture show schematic more accurate. Pair of brown and blue wires are split to: Brown/White + Blue/White = GND Brown + Blue = +12VDC Because wires are twisted, magnetic flux around pair of wires is minimised. Orange = +Video Orange/White = -Video On schematic diagram, at signal harness: Blue, Orange, Green, Brown represents each pair of wires.

Sorry, but i do not understand You. Can You explain me more detail. Thanks.

Mine too. I have thought about it, but my guess is that, if there is ground loop problem, problem should exists always, because potential difference between two different points (in my case, camera and DVR) should exists always, during IR LED working or non working period, or i make mistake. My guess is, some of these two cameras have some kind internal supply for IR LEDs, some BJT or FET transistor and some circuitry around it, that produce HUM on power supplies wires, and dc adapter can not reduce that HUM. I cannot access place during low light conditions to make some tests (or i can, but only once, and than i need to explain reason, and if i do not solve problem, it is going to be problem for me ). So, i have one chance to solve problem. If some camera has faulty circuitry which produce HUM when i disconnect it from dc adapter, hum should disappear, but if it is not, i do not know what to do next, and what should be my plan B or C. Plan B would be ground loop isolator, but i hope it is not that, if it is i will need to pay for two of these 39€(54$) .

Cat 5, 24AWG, CCA

As I mentioned before. I have already replaced power supply twice. First, there was 12VDC 3A, second was 12VDC 3A and third time i have installed 12VDC 2A from different supplier. This supply just two cameras, and there is similar situation at this place, where 12VDC 2A supply another 2 cameras, very similar to this 2 which have hum bars during low light conditions. Also, during cameras adjustment, i have been used test monitor which i have supplied from same dc jack connector at camera place, at that moment there were 2 cameras + test monitor, for which i suppose, current consumption is about 1A DC. During these tests hum bars have not appeared in picture.