CCTV Cameras Interference when cameras powered by same PSU

[Speakercon]

Hi, I have installed a simple 4 camera CCTV kit, (4 x 12V IR cameras + a DVR), and am having a problem with interference (lines running through the screens and even a faint image of another camera over the top of another cams image.

This only happens when the cameras are powered by the same transformer (12V 3A), when they are powered by 4 separate transformers they work fine, but then put 2 or more on one and the problem happens.

I have tried a different main transformer, that does no good.
The only alteration I made to the kit was to use CAT5 and balums instead of the BNC/Power cables that come with the kit (for ease of threading through holes, ect), but I can't see as this is the problem as the picture quality is fine if separate transformers are used.

If anyone has any ideas why this is happening I would be most grateful for ideas!

I am thinking it's maybe a earth loop problem and I'm currently researching way of overcoming this but thought I'd ask here for any personal experience.
Thanks!

 

[Speakercon]

Update - I've now fixed the problem by putting the DVR and camera's on the same 12V 5A transformer which I assume has removed the different ground potentials and thus removed the ground loop problem.

If anyone could confirm my thinking is correct it'd be nice to know!
Thanks.

 

[chaindaisy]

I would have assumed that they should all be on the same transformer in any case.

 

[Jibbeh]

Do you have a battery powered test monitor and are the pistures all present and correct when viewing them one at a time through it? (using the 5a psu)

 

[TheAlarmMan]

Have you sent power down the Cat5 with the video?

Using the same power supply for the DVR and cameras is not a good idea.

Are you using a switch mode PSU for the cameras?

How long are the runs? I'm assuming short? Do they run with mains or passed switched mode supplies?

AC or DC ? Assume DC as your powering the DVR?

You will only get hum bars when using different supplies, like 3 phased systems, so one building is on 1 phase and building 2 is on phase 2 and is powered locally.

 

[Speakercon]

Do you have a battery powered test monitor and are the pistures all present and correct when viewing them one at a time through it? (using the 5a psu)

Not got a test monitor, and yes they work perfectly one at a time.

 

[Speakercon]

Have you sent power down the Cat5 with the video?

Using the same power supply for the DVR and cameras is not a good idea.

Are you using a switch mode PSU for the cameras?

How long are the runs? I'm assuming short? Do they run with mains or passed switched mode supplies?

AC or DC ? Assume DC as your powering the DVR?

You will only get hum bars when using different supplies, like 3 phased systems, so one building is on 1 phase and building 2 is on phase 2 and is powered locally.

Yes sent power down as well as video and have used a twisted pair for video and a twisted pair each for + & -

It is a switched mode DC PSU & the runs are about 10M each.

Why is it not a good idea to run the cameras & DVR from the same transformer btw?

 

[chaindaisy]

We run from the same psu, sometimes as many as ten cameras per psu and have never had any problems, would appreciate the reasoning though ?

 

[Jibbeh]

Get yourself a test monitor, battery powered and a neccessary tool for anyone that regularly does cctv.


I'd double check your connections too, a missing negative on either power or negative side of balun wiring would cause problems similar to yours. Try unplugging each camera bnc in turn from your dvr and check only one camera disapears.

 

[TheAlarmMan]

I would never use the same PSU for the cameras and DVR, for a start if someone chops the cable or shorts it you lose the lot.

Then you've got current capacity issues.

Best practice is not to send power down the Cat5 along with signal as this can effect the video although over these short distances it shouldn't be a problem, also you should not pass signals in opposite direction.

 

[chaindaisy]

I'm a bit confused ! The cameras in say a maplin 4 camera kit are linked to the dvr, for example, and their power, I assume is from that dvr, is that correct or not ? If it is correct then they share the same power supply. As far as our commercials are concerned, monitors, sequntials and PC's etc are all mains driven, with cameras often sharing the same trade supplied power supply, which could be any distance from the main units.

 

[plugwash]

When you used a seperate power supply for the cameras and the DVR did you connect their grounds together?

 

[Jibbeh]

Why thats just blatent bump whoring Mr Plugwash.

 

[Europlex]

...............................lines running through the screens .......

Are any of the cables running alongside mains (240v AC) cables?

Induction causes your problem.

 

[plugwash]

Why thats just blatent bump whoring Mr Plugwash.

Sorry, not sure how I ended up at this thread and didn't realise it was so old.