Multiple cameras - single PSU.

[p3ter 0]

Hi, It's my first post here!

 

I have been trying to find information about powering multiple cameras with a single PSU, and I've noticed a number of internet shops selling pigtail style 12v connectors, allowing you to power multiple cameras with a single power supply, but the the shops that sell these never give any information about how/when they can be used, or what the limitations are.

e.g. sctltd.co.uk / acatalog / WiringPower . html

From my (poor) understanding of electronics, I know that a simple device like this will not isolate one camera from another, and in the end, you will create one big circuit. This may not be a problem if all cameras are the same make & model, and have the same length cable runs, but what happens if the devices have different current demands, or even simply different lengths or gauges of wire?

 

I have 4 cameras connected to a Geovision GV250 card, all the cameras have IR LED's, and all draw between 280ma to 500ma. The longest cable run is 25 meters, but I also have a 15m, 10m, and 2.5m cable run. Only 2 of the cameras are the same make/model, but even these are on different length cable runs.

 

I have tried simply wiring a number of cameras to a single regulated switched PSU (12V 2A), but with limited success. (well I suppose the fact that I have not ruined any cameras yet is pretty successfull!)

It seems like some of the cameras work together, but others either 'switch each other off' (plugging in one causes the image to black out on the other), or sometimes trip the PSU. I have had more success with cheaper (regulated, but not switched) PSU's, but it just doesnt feel like a safe solution...

 

I have tested all connections, and I don't have any wiring faults, so it seems like it is the interaction between the different cameras that causes the problems.

 

I have seen the big tin cubpoards you can get (Pelco and others) which of course would solve my problem, but I already have more than enough power supplies

 

I have also seen that there are devices that simply act as regulators, with some kind of physical or thermal fuses.

 

OK I've rambled on enough... maybe to try ask some specific questions..!

* when can simple pigtail style cables for mutiple cameras safely be used?

* what do you think is happening when I plug in one camera and the other camera switches off?

* what are the basic requirements for safely running mutiple camers off one PSU?

* is there a simple & cheap device I can buy that will allow me to run multiple cameras safely off a single 'run if the mill' switched 'laptop brick' style PSU?

 

Thanks for any pointers!

 

Peter

[kao 0]

12v DC is polarity sensative. Make sure you have all the right connections.

Usually solid black wires are the negative (for DC) as well as the outside ring if you are using a barrel connector.

Positive leads are usually a black with a white stripe (sometimes they are solid red or solid white) and are the inside pin on a barrel connector.

[kensplace 0]

Whilst powering many cams off one 12vdc supply is a cheap way to do it, it has a big drawback, if one wire shorts out, or one cam shorts out, all your cams go down at once.

 

As long as all cams are connected properly, and the wire runs are not too long (for voltage drop) and you dont exceed the current rating of the psu, then there should be no problem powering multiple cams.