having issues with Noise/waves when using centralized power

[BrownChiLD 0]

Hi guys

 

I've been battling w/ issues of noise and all sorts of problems when using centralized power supply, and I'm finally posting for some ideas..

 

Hardware

700TVL Analog CCTVs over UTP Cat5e or Cat6

Standard video and passive power balun

 

DVR

 

Centralized PSU

 

12v DC Adaptors

=> 0.5A

=> 2A

=> 5A

 

 

I have 2 main example scenarios (different situations but same catalyst for issue = centralized power)

 

SCENARIO 1) LONG RANGE ISSUE

4CH System, 3cameras under 50m length and 1 camera at 130m length

 

PROBLEM:

If using a centralized POWER SUPPLY UNIT for all cameras, cameras deployed over 120m> gets noise with lines running up the screen (this is both on live view as well as recorded = so no it's not monitor/display issue)

 

What I've tried (didnt fix the issue):

- different centralized power supply brands/models, etc..

- tried using just 1 camera (the far one)

- tried several different brands of UTP cables

 

SOLUTION:

For the far camera we use a dedicated 12v DC adaptor (1.5A)

 

Is this normal? if it's power issue the centralized PSU is actually built for 16-18Ch and i'm using just 4 cams on it.. and even if i use just 1 on it. it's the same problem

 

 

SCENARIO 2) Issues when putting 2 or more cameras on the system.

When using 2 or more cameras on one centralized power supply causes "waives" to appear on the display as well as recording..

 

This is a different issue from #1, I am working w/ a new batch of camers and powersupplies and i can't seem to reproduce issue #1 .. but instead i get this new power related issue w/c i think is worst..because even on short cable runs.. the moment you add 1 more camera to the system this happens.

 

video here: https://www.dropbox.com/s/u391h1dui472dym/Video%208.wmv?dl=0

 

 

What I've tried (didn't fix the issue)

- try different centralized PSUs..

- tried 3 different utp cables

- try high-cap (2A and 5A) 12v DC Adaptors (as centralized psu) with 1 to 4 spliters..

- tried shorter cable lengths (40m 60m 80m)

 

SOLUTION

We use a dedicated 12v DC adaptor (0.5A) for EACH camera to resolve the issue. (WTF)

 

 

So this has got us scratching our heads because we've seemed to ruled out the following:

1) Centralized PSU has interferences

--> Nope. because even split type 12v adaptors has the exact same results

 

2) insufficient power?

--> can't be.. even just 2 cameras on the 2A and even 5A power adaptor has issues

 

3) Cable issue

--> tried different cables.. and if it's the cable, how come using a single dedicated adaptor works fine?

 

4) DVR?

--> same as #3

 

5) camera

--> doesn't make sense but we're gona try other analog cameras.

 

 

 

Soo yeh we're stomped. What do you guys think is the problem here?

[jazzar 0]

you need to measure the voltage that is present at the camera, the small core size of the twisted pair cable will have more resistance which will cause a voltage drop across the length of the cable. you might only be getting 10v or 9.5 volts at the camera terminals.

usually these type of injectors are designed for 48v dc ip cameras which will generally operate from 24v to 48v and will handle the voltage drop across the cable.

If your voltage is low at the camera terminals then this may be part of your problem, you could easily try hooking up a 12v battery locally at each of the camera ends and see how it goes.

Siamese cctv cable (co-ax with two core attached power cables for 12v or 24v supply) are usually a bigger cable gauge to provide less voltage drop.

maybe this will help.

[Horizon 0]

Hi BrownChiLD.

Sounds like you've got a ground loop problem.

The power ground is in parallel with the video signal ground.

Can your cameras work with both 12VDC and 24VAC, or only 12VDC?

The cameras that only work on 12VDC usually have an internal power supply that is grounded, which means that the video output ground and the power ground are connected together, which forms one end of the ground loop.

The other end of the loop is at your central power supply, where all of the camera power grounds are usually tied to the mains ground. The DVR case is also tied to this ground, as is the DVR video input ground, via the BNC sockets.

 

CAT5 twisted pair cable requires balanced signals, in that the video signal goes to the DVR along one half of the pair, and the return signal travels back to the camera along the other half of the pair, completing the circuit. The twists ensure that any interference occurs identically on both halves of the twist, so it can be cancelled out at the DVR end by the other balun.

With the ground loop, some of the video signal is returned along the power ground. Interference from the power ground is added to the video signal, and can't be cancelled out, so it messes up the picture.

 

The ground loop can be broken at the camera, or at the power supply.

 

The cameras that can handle both 12VDC and 24VAC tend to be immune to ground loops because their internal power supply is transformer-isolated from ground, which breaks the ground loop. So if you swap out a 12VDC-only camera for a 12/24 camera, that could fix your problem.

The other solution is to use separate power supplies, as you've found out.

[crincones 0]

I am having the exact same problem,

 

installing runs of about 90m, with cameras at every 10 meters or so, UTP for video and paralell wire at 12VDC for power..

 

had problems first with the UTP cable, buyed poor chinese cable, and after installing most of it and getting bad results, resolved to test the resistance.. for good quality UTP cable should be around 30 ohm every 300m.. my box of cable was incomplete (about 140m left) and tested it.. the brown and blue pairs returned 680ohm.. and the green and orange, around 220 ohm.. so.. spend a little more and buy some good quality UTP, made of COPPER, and not aluminium with copper surface.. (scratch it with a knife and will show)..

 

well, second flaw. installed a long run of power paralell wire at 12V (longest run with 90m, same wire used in extensions), and tried to take power from it to the cameras, all connected in paralell with that wire.. horrible results, cameras worked like charm in daylight, but at night.. horrible noise.. the voltage dropped too much, to less than 10 volts.. (normal current consumption: 100mA daylight, 300mA night with IR on).. it is always good to test amperage before installing to make correct cable calculations..

 

bought something like AWG14 wire for power, but when tested resistance (after installng).. crappy results, like 4 times the expected resistance (chinese wire), resulting in something similar to an AWG20 wire..

 

So.. broke it at the half of the run, and installed a separated power supply (installation permitted it) for the second half of the run, and that solved the problem, but without discovering the cause..

 

the weird thing is that when I connected more than 4 cameras in the same power cable (even when testing the power supply in the center of the run (same distance in every directon), got noise in all of them, less than that, no noise.. thought the power supply was overloaded and injecting that noise, but tested amperage and got around 1.4A (for a 10A power supply), and normal voltage on load...

 

I doubt I will try this paralell cable scheme, was not good at all, will try to stick to UTP cable using as many pairs as required for power.. calculating the maximum voltage drop, of course.

 

my advice.. TEST YOUR CABLE if its from an unknown brand..

 

any clues of the weird interference? will be happy to hear about it..

[Ninety 0]

 

Try one of these ... I bet it fixes it.. there are much better solutions but as pointed out above.. it is a ground loop issue.

 

Ground loop isolator

 

[joseph.chen0312 0]

Scenario 2 seems not power issue but color rolling/breathing.

 

Can you share scenario 1 footage let folks see how, even interferenceand and noise may caused by diverse factor.