CCTV

[solarman216]

anyone out there, up on this stuff, I have 4 cameras that till now have run on individual mains transformers, but in the interests of economy have linked them all together on one 12volt supply but now I am getting interference between cameras, so the question is can I sort this with a diode on each cameras feed or is it not as easy as that, I ask because they are spread over a large area and to simply experiment will take an age, Rick

 

[R1cho]

what sort of interference?

 

[briggie]

many reasons for interference on cctv mate , anything from bad earth on power supply to cams being too close together , to poor screening , are yours on a clean dc supply ?

 

[briggie]

an easy check to make is to disconnect the coax from both ends ..... ie from the camera and dvr ... put a multimeter between inner and outer cores ..... should read infinity , if it doesnt ..... there is your problem

 

[solarman216]

many reasons for interference on cctv mate , anything from bad earth on power supply to cams being too close together , to poor screening , are yours on a clean dc supply ?

yes because we have been converting from 24v dc up to 240 ac then going from that down to 12 v dc per camera I thought right I will take a lead off the 12 volt bats that only supply the fridge and supply the cameras from that, great but now I have heavy vertical or horizontal interference using the same video leads as before so it is clearly to do with 12 volt supply problems to all the cameras, so I assume I need to separate them some how, hence the diode idea, would a diode on just the positive lead do the job or would I need to put one on both leads, Rick

 

[briggie]

perhaps ,or a rectifier

 

[briggie]

right thread this time lol

a bridge rectifier found in psu's is basically 4 diodes anyway to clean a supply

 

[briggie]

its late and im tired and not thinking straight , but that assumes you have spikes or troughs , suppose no harm in trying it .... i need bed

 

[solarman216]

its late and im tired and not thinking straight , but that assumes you have spikes or troughs , suppose no harm in trying it .... i need bed

you go to bed mate, there is no hurry, Rick

 

[Terranoman]

Is the 12 volts now running further?

ie before was the power supply at each camera location and now power cables extended to the new power supply?

Try a different transformer.

Does the power cables run past something that could be causing the issue? ie fridge or another transformer?

Is everything on a clean power supply?

Try unplugging each camera's power to see if it stops. try from the transformer first.

 

[briggie]

ok , now im awake lol , ive just read your post properly rick .

fridge/freezers are notorious for causing interference on supply ..by the very nature that they work .

first things to check .......

check the dc voltage at the cams is exactly what is required for the cams ( not under and not over )

secondly ....

try a different dc source than from the fridge supply

im assuming from your post that you are not using a transformer as such but a invertor from 24 vdc ...to 240ac, then down to 12vdc.

is your generator running while the interferance is happening ? or is it happening all the time regardless of whether the genny is running or not ?

try the seperate dc supply than that from your fridge etc first mate

 

[the4x4steve]

sounds like an earth fault
i had a very similar problem in a pub about a month ago the psu was shorting the earth with the supply and giving interference

 

[clivvy]

we sell cctv at our spot, from what i hear my collegues say, if the distance is quite large, then the 12v you are feeding to all 4, wont be enough, as you need a higher voltage for each camera if they are a distance away.

im no expert though, its just what i hear, the interference is probably lack of power

 

[solarman216]

had a bit of a play this morning, but still no joy, have good voltage right up to the last camera 200 mtrs away, I have tried putting diodes in the power line to each camera, but no different, I have the first camera and the last camera working OK but the other two just screw the last camera up so I think it is because the screening is common to the last three, camera one comes in on its own screened lead, strange that it worked perfectly when the last three cameras were on individual power supplies, the 12 volt by the way is direct off of the batteries, so looks like I will have to run individual screened leads, or go back to power supplies but these then run of the inverter which is what I am trying to reduce, Rick

 

[clivvy]

from what I know (very little) you will be on the right track if you go back to individual power to each camera. 200 meters away is quite far, so im 99% sure you need a higher voltage to the camera...perhaps 24v im not sure??

 

[briggie]

advice from a colleaugue

Difficult to be sure as I don't really know how it is all wired,... anyhow:
A separate supply ground is a must.
The video ground should not share the same ground cable as the supply, so ensure the video is separated, ideally with coax from each cam. back to monitor etc,

Golden rule with this kind of stuff is to wire everything in a point to point fashion, do not daisy chain the power cables from one cam to the next. (no matter how convenient i may be!)

So in short each cam should have a coax for the video and a separate supply lead to each cam originating from the 12V supply.

That may sort it out, as I feel it is a "ground loop" issue.

I'll leave you to paraphrase this and give Rick some ideas.

 

[solarman216]

Sorted it, placed a 100uf capacitor across the supply to each camera, now have 4 good pictures again, Rick